Nature Unbound II: The Dansgaard- Oeschger Cycle

by Javier

Dansgaard-Oeschger (D-O) events are the most dramatic and frequent abrupt climate change events in the geological record. They are usually explained as the result of an Atlantic Ocean salinity oscillation paced by internal variability. Available evidence however supports that they are the result of an externally paced oceanic-sea ice interaction in the Norwegian Sea. A lunisolar tidal cycle provides an unsupported hypothesis that explains all of the known evidence for the 1470-year pacing and the triggering mechanism for D-O oscillations.


A review of geologically recent abrupt climate changes provides a frame of reference for current global warming. The glacial cycle was reviewed in a previous article in this series. In this article, we review some abrupt changes that characterized the last glacial period. They are relevant because some scientists believe they may be related to millennial climate variability taking place during the Holocene, and thus constitute part of the background to present climate change.

It was already known by palynologists early in the 20th century that pollen records showed abrupt climate changes at the end of the last glacial period. The records marked alternating cold (stadials) and warm (interstadials) periods. The last two stadials were named after a tundra flower whose pollen became abundant, Dryas octopetala, as the Older Dryas and the Younger Dryas.

In 1972, after analyzing the isotopic composition of ice cores from Camp Century in Greenland, Willi Dansgaard reported that the last glacial period showed more than 20 abrupt interstadials marked by very intense warming (Johnsen et al. 1972). The discovery was met with indifference by the scientific community still struggling to identify Milankovitch cycles in the data, because the new abrupt changes were not found in Antarctic records. Twelve years later Hans Oeschger reported that the abrupt changes were accompanied by sudden increases in CO2 in the Greenland ice cores (Stauffer et al. 1984). From then on the abrupt changes were known as Dansgaard-Oeschger (D-O) events. It was later decided that Greenland’s elevated CO2 records were the result of chemical contamination, since they did not match Antarctic CO2 records.

Dansgaard-Oeschger oscillations.

The good temporal resolution of the GISP2 ice core, where the annual ice layers can be counted, showed that D-O events were oscillations of a 1470-year cycle (Figure 18. Schulz, 2002).


Figure 18. The Dansgaard-Oeschger cycle. Dividing the 50-10 kyr BP period in boxes of 1470 years clearly shows the periodicity of the DO cycle, that has less than 1% probability of being due to chance. The deviation for the later, best dated, oscillations from the period is of only 2%. Source: S. Rahmstorf, 2003. Geophys. Res. Lett. 30 1510-1514.

D-O oscillations are the most dramatic and frequent abrupt climate changes in the geological record. In Greenland, D-O oscillations are characterized by an abrupt warming of ~ 8°C in annual average temperature from a cold stadial to a warm interstadial phase, followed by gradual cooling before a rapid return to stadial conditions. Initially they were thought to be a regional phenomena, since they were not prominently displayed in Antarctic ice core records, however evidence uncovered since shows that they display a hemispheric-wide climate effect reaching into the southern hemisphere (figure 19).


Figure 19. Widespread effects of Dansgaard-Oeschger cycle. (A) Warming in Greenland is coincident (red dots) with warmer wetter conditions in Europe, higher sea-surface temperatures in the western Mediterranean. increased precipitation in the Venezuelan coast, enhanced summer monsoon in the Indian Ocean, aridity in southwestern North America and China, changes in ocean ventilation in California, increased sea temperature and productivity in the Arabian sea. Warming in Greenland is also coincident (blue dots) with anti-phased cooling in Antarctica, and the circumpolar seas. Yellow dots, places were evidence has been found for the Younger Dryas (YD). Source: W. Broecker. 1999. Updated. (B) Modeled changes in temperature for the stadial-interstadial transition. (C). Modeled changes in precipitation for the stadial-interstadial transition. Source: L. Menviel, et al. 2014.

D-O oscillations are not the only climate change taking place during the last glacial period. Temperature variability is very high (figure 20A and B), and the changes have different shapes, durations and spacing. They are sometimes separated by other intense climate changes of a different nature called Heinrich events. Let’s describe those changes starting with Greenland.

With a periodicity of ~ 6,000 years (figure 20 turquoise) 1-4 kyr Heinrich events (HE) took place in the north Atlantic region, causing a drop of 2-3°C from the already cold glacial climate. Sea surface temperatures in the North Atlantic dropped to what are now arctic conditions as far south as 45°N, and were probably covered by sea ice during the winter. At the end of Heinrich cold events, in a relatively short period of a few centuries at most, a huge armada of icebergs was produced from the Laurentide ice sheet, or less often from the Fennoscandian one. The icebergs carried huge amounts of eroded material that deposited ice rafted debris (IRD) on the sea bed when they melted. Heinrich events are labeled H0 to H6 (figure 20), with the most recent coinciding with the Younger Dryas.


Figure 20. Chronology of climatic events for the Last Glacial Period. (A) Greenland temperature proxy. Red numbers denote D-O events. (B) Antarctic temperature proxy. A1 to A7, Antarctic warming events. (C) Antarctic atmospheric CO2 concentrations. (D) CH4 concentrations from Greenland (green) and Antarctic ice cores (brown). Vertical turquoise bars, timing of Heinrich events (H3 to H6). Brown dotted lines, abrupt warming in Greenland. Source: J. Ahn, and Brook, E.J. 2008. H0 to H2 S.R. Hemming, 2004.

A Heinrich event is followed by the triggering of a D-O interstadial warming. Even if only one in four D-O oscillations is preceded by a Heinrich event, all of them appear to have been preceded by a similar, albeit reduced, cooling and IRD deposition in North Atlantic marine sediments. Gerard Bond suggested that Heinrich events are part of the D-O cycle (Bond et al. 1993). Since Heinrich events involve more profound cooling and much more intense ice-shelf calving we can therefore distinguish between HE D-O oscillations (numbers 1, 4, 8, 12, 14, 17) and non-HE D-O oscillations.

D-O oscillations are characterized by their asymmetric change in temperatures. They all display a very fast warming, with temperatures rising by about 8-10°C in just a few decades, within the span of a human life time (figure 21). This warming, in less than a century, is followed by a slower cooling of ~ 2°C in about 200 years. From this point D-O oscillations take different paths. Some D-O oscillations will quickly drop 6-8°C into cold glacial temperatures in about 250 more years for a total span of ~500 years. Other D-O oscillations will take 500 to 800 years to complete a more irregular descent, for a total span of 800-1000 years. Finally, some D-O oscillations will take more time to go back to the glacial stadial baseline than the length of a cycle. In such cases new D-O oscillations are prevented from taking place until the cooling ends. One of the greatest difficulties that D-O models face is explaining how such a wide distribution in cycle duration occurs when the warming phase has a precise pacing of 1470 ± 8%. In the recent, best dated, cycles the warming phase variability is only 2% (Rahmstorf, 2013).


Figure 21. Time evolution of recent D-O oscillations. D-O oscillations show a very abrupt warming phase followed by a slow cooling phase. Afterwards a more abrupt temperature drop usually follows while oscillations display variable length of the last cooling phase. Source: A. Ganopolski, and Rahmstorf, S.

Dansgaard-Oeschger oscillations in the Antarctic record.

When studying the D-O cycle in Antarctic records it became apparent that Greenland temperature changes matched methane level changes at a global scale (figure 20). Since methane levels were skyrocketing simultaneously in both Greenland and Antarctic ice cores, this provides a precise way to align both records (Wais Divide Project Members 2015).

The alignment of Antarctic and Greenland records shows that there is an inverse temperature relation between both poles. During a D-O cold phase temperatures rise in Antarctica. This rise is especially intense if the stadial is a Heinrich event. Temperatures in Antarctica peak 220 years after the D-O transition triggers in Greenland (Wais Divide Project Members 2015; figure 22). This delay suggests an oceanic link between both poles. Afterwards temperatures go down simultaneously in both poles, but Antarctic temperatures bottom early and start to raise again in preparation for the next cycle.


Figure 22. Cartoon of the D-O interpolar phasing of temperatures. During a Heinrich event Greenland temperatures (blue) get very cold, while they rise in Antarctica (orange). Once the abrupt warming takes place in Greenland, temperatures peak in Antarctica on average 220 years later. If the previous Antarctic warming has been very intense, as in D-O 8, the Arctic cooling can take much longer and then one or more cycle periods are skipped until temperatures are cold enough. Source: T. van Ommen, 2015. Nature 520 630–631, based on data from WAIS Divide Project Members 2015. Nature 520 661–665. Modified.

How is this temperature connection achieved? The planet receives most of its energy from the Sun in the tropical areas. Much of this energy, converted to heat, must be directed to the poles, where the surplus heat can be radiated to space. Two thirds of this meridional heat transport is achieved via the atmosphere and one-third via the oceans in the Meridional Overturning Circulation system (Trenberth & Solomon, 1994). This circulation mechanism transports heat as warm surface currents to the poles, that return as cold deep currents after they ventilate the heat to the polar atmosphere. What makes the meridional heat transport function is the temperature gradient between the tropics and the poles.

Pacific warm waters are mostly prevented from reaching the Arctic, so the only effective connection is through the North Atlantic between Greenland and Scotland. The closure of the Panamanian Pacific-Atlantic connection converted the North Pacific Ocean into a cul-de-sac for the meridional heat transport. The South Atlantic is the main ocean transporting heat northward across the Equator, making the Atlantic an avenue for warm surface waters that originate in the Southern Ocean to go to the Arctic ocean and return as deep cold water. This is the temperature connection between the poles. It has been proposed that when the Atlantic current is strong it cools the Antarctic and warms the Arctic by changing the energy budget in favor of the latter, and when the Atlantic current is weak it warms the Antarctic and cools the Arctic. This heat-piracy hypothesis is the basis of the bipolar see-saw model, that is supported by available evidence on the changes of the Atlantic Meridional Overturning Current (AMOC; Stocker and Johnsen, 2003).

The explosive growth of methane during D-O oscillations raised fears that abrupt climate change has repeatedly triggered the hypothetical clathrate gun and that it could happen again in the near future. However deuterium isotopic analysis of ice core methane has shown that the increase in methane was accompanied by a depletion in deuterium (Bock et al., 2010; figure 23). This depletion indicates that its origin is deuterium poor methane from boreal wetlands; one of the main natural sources of methane, and not from deuterium rich clathrate hydrates. The increase in temperatures and precipitation associated with the D-O cycle (figure 19b and c) is then responsible for boreal wetlands expansion and CH4 emissions.


Figure 23. Methane changes and origin during D-O cycles. Top panel shows a temperature proxy from Greenland. The second panel shows CH4 records from Greenland, GRIP (Greenland Ice Core Project) (purple diamonds), NGRIP (orange diamonds), and Antarctic EDML (blue diamonds). Deuterium δD(CH4) values in the bottom panel are from the NGRIP ice core (orange circles). All data sets are given on an age scale after CH4 synchronization. The green bar indicates the Heinrich 4 event (H4). Changes in methane levels are inversely correlated to methane deuterium content, indicating a deuterium poor source, most likely boreal wetlands. Source: M. Bock, et al. 2010.

Some scientists believe CO2 is the main agent responsible for temperature changes not only in the present, but also in the past. Curiously Antarctic ice core records do not register any contribution or response from CO2 to the most frequent abrupt changes of the past, the D-O cycles (figure 20). CO2 levels only increase during Heinrich events. As we have seen Heinrich events are associated with Antarctic warming while the North Atlantic region cools several degrees and iceberg discharge increases dramatically. Since the Antarctic region is the only one warming during a Heinrich event, it is generally believed that the increase in CO2 is from enhanced CO2 ventilation from a warming Southern Ocean (Ahn and Brook, 2014).

HE D-O and non-HE D-O oscillations display different CO2 changes during their previous stadial cold phase (figure 24a and b). In Antarctica this cold phase is manifested as warming for all D-O oscillations (except D-O 9; figure 17, b). However only HE D-O oscillations display an increase in CO2. Non-HE D-O oscillations do not show any increase in CO2 levels (figure 24a). The contrast in the behavior of both types of events is more evident when changes in CO2 are plotted against changes in temperature (figure 17, c). This result suggests that it is Heinrich event cooling in the North Atlantic that is causing the Southern Ocean to warm and release CO2, and not Antarctic warming, which is unrelated to CO2 levels.


Figure 24. Time evolution of CO2 and Antarctic temperature during Greenland stadials. (a) CO2 change during Greenland stadials from Antarctic ice core records. DO numbers indicate D-O warming events at the end of the stadials. (b) Antarctic temperature proxy record during Greenland stadials. (c) Time evolution of atmospheric CO2 versus temperature anomalies during stadials. Derived from (a,b). The pale red and blue ellipses indicate records for Heinrich (long) and non-Heinrich (short) stadials, respectively. Three hundred-year running means are used for both CO2 and temperature proxy records. In order to remove multi-millennial changes during short Greenland stadials, the Siple Dome CO2 and temperature proxy records are detrended. D-O 9 (pink in b) is not considered a true D-O oscillation by several authors (see text). Source: Ahn, J. and Brook, E.J. 2014. Nature Communications 5, Article number: 3723.

We can conclude that, according to available evidence, CO2 plays no role at all in the most abrupt and frequent climate changes. The D-O cycle and the increases in CO2 observed in Antarctica associated with Heinrich events appear to be a consequence of Southern Ocean warming, and neither a cause nor consequence of Antarctic warming. Furthermore, the increase in CO2 during Heinrich events (of about 10 – 15 ppm) does not appear to significantly alter the rate or magnitude of the warming during the subsequent D-O oscillation (see for example, in figure 24 that DO4 warming is like the rest).

Conditions for Dansgaard-Oeschger cycles.

Some authors have disputed the existence of a regularly spaced D-O cycle on the basis that the oscillation distribution is not significantly different from random (Ditlevsen et al., 2007). There is some difficulty in correctly dating, with sufficient precision, oscillations that took place so long ago. It is significant that the most recent oscillations show a better periodicity. Additionally, the ice record that shows the most robust periodicity is GISP2, the Greenland ice core with the best temporal resolution since its annual snow layers can be counted. Finally, the abrupt climate oscillations that are part of the D-O cycle have to be properly defined. A D-O oscillation requires several signature conditions. It is highly asymmetric with rapid warming for a few decades and slow cooling over at least 200 years followed by rapid cooling for at least 200 more years for a minimum duration of 400 years. It is matched by a similar peak of methane levels of similar amplitude and duration. And it is preceded by prior Antarctic warming that peaks about 220 years after the Greenland warming peak. Most mathematical analyses fail to include this signature and thus consider peak number 9 as a D-O oscillation when it clearly is a different type of abrupt warming (see figures 18 and 24b). Its elimination from the analysis greatly increases the robustness of the cyclicity.

Since D-O oscillations, as previously defined, are a glacial feature, they appear to be influenced by global temperatures and therefore by orbital changes. D-O cycles are suppressed at warm times of maximal obliquity at 90, 50, and 10 kyr BP and at very cold times after minimal obliquity at 65 and 20 kyr BP (figure 25). So it appears that D-O abrupt changes cannot take place when the world is warm or very cold.

Schulz et al. (1999) investigated the irregular distribution of D-O oscillations during the past 100 kyr by extracting a 1470-year signal from GISP2 temperature proxy data using time-frequency analysis through harmonic filtering. The resulting signal (figure 25A) shows four periods of higher amplitude separated by minima at 80, 65, 50, 20 and 10 kyr BP (figure 25B arrows). Each period of higher amplitude corresponds to periods of D-O oscillations. They then noticed a strong relationship between the 1470-year signal and variations in continental ice mass, as recorded in sea-level variations. Each of the five minima in the 1470-year signal corresponds to an inflection point in sea level variation and four of the five take place when sea levels are above -45 m or below -90 m from present level (figure 25B). The fifth at 50 kyr BP coincides with a maximum in obliquity.


Figure 25. D-O oscillations and changes in sea levels. (A) Top: Temporal changes of the 1470-year signal component in the temperature proxy record estimated by a harmonic-filtering algorithm using a sliding rectangular window of width 4 x 1470 yr. Bottom: Temperature proxy record from Greenland GISP2. Numbers indicate D-O oscillations. (B) 2000-yr smoothed amplitude of the 1470-yr signal (dashed line) and sea level (red). Amplitude increases sharply as sea level falls below -45 m and decreases when sea level falls below -90 m. Pronounced amplitude minima coincide with local minima or maxima of sea level (arrows). Source: Composite of figures 1 & 2 from M. Schulz et al. 1999. Obliquity and -90 m sea level band added.

So since the conditions for D-O oscillations can be shut down, for example during the Last Glacial Maximum, and upon being restarted they still maintain the same 1470 year pacing, this is a strong indicator that the trigger for the D-O cycle is external, and its clock is always ticking. The right conditions for a D-O oscillation require the build up of extensive ice sheets over the northern continents that cause a drop in sea levels of at least 45 m. Once that happens, the bipolar see-saw must be set to warm Antarctica and cool the north polar regions. These conditions will extend the sea ice cover over ample regions of the Nordic seas and North Atlantic and produce an increase in iceberg discharge. Then the next tick of the clock will trigger a D-O cycle. Whenever those conditions are reset a new D-O oscillation might be triggered. Warming from obliquity maxima will prevent the conditions from taking place, as will a profound cooling that reduces sea levels below -90 m producing too much ice.

Consensus Dansgaard-Oeschger cycle theory and challenges.

The consensus theory on the D-O cycle was established by Wallace Broecker (Broecker et al., 1990), and is defended by one of the leading experts on abrupt climate changes, Richard Alley (Alley, 2007). It is known as the “Salt Oscillator” hypothesis, and it is based on oscillatory changes of the Atlantic Meridional Overturning Circulation, or AMOC, in response to fresh-water pulses due to water from melting ice (melt-water pulses, MWP) being stored and released periodically from ice-sheets (figure 26).

The AMOC is controlled by warm sea surface waters of its North Atlantic Current component (NAC). This warm water becomes more saline through evaporation in the Atlantic basin and in subarctic regions. The water becomes colder and denser in the subarctic until it becomes dense enough to sink and turn south to constitute the cold North Atlantic Deep Water (NADW) component. The intensity of the NADW determines the state of the AMOC. The term Thermohaline Circulation (THC), introduces confusion as it refers only to the thermal and salinity effect on the circulation, ignoring the wind and tidal effects also included in AMOC, since they are difficult to separate. It is better to use the term “AMOC” instead. Global conveyor and MOC (global Meridional Overturning Circulation) are interchangeable terms.

The NADW then flows southward along the bottom of the Atlantic Ocean transporting the excess salt, resulting in a gradual reduction in North Atlantic surface salinity over time. Furthermore, tropical heat transferred to the high-latitude North Atlantic produces ice melting and MWP that further reduce water salinity. If surface waters at the sites of deep-water formation become too fresh, then AMOC weakens or shuts off because the surface waters are not dense enough to sink. Once AMOC weakens enough or even shuts down, salt starts to accumulate again in the North Atlantic due to the absence of NADW export. According to this theory, weak AMOC conditions are associated with cold stadials (figure 27).


Figure 26. The salt oscillator hypothesis. Left, During warm interstadials, a strong AMOC transports heat northward causing the ice sheets around the North Atlantic to melt, gradually reducing surface water salinity until it no longer sinks and deep water formation ceases, stopping the NADW. Eventually, surface salinity is reduced enough to weaken AMOC, shifting the climate into a cold stadial. Right, During stadials, cooler conditions in the North Atlantic reduce meltwater input from the ice sheets, allowing an increase in surface salinity that eventually causes water to sink restarting NADW and causing AMOC to strengthen, returning the climate system to an interstadial. Source: Ruddiman, W.F. 2000. “Earth’s Climate: Past and Future” First ed. W.H. Freeman ed.

As salt continues to accumulate in the North Atlantic during periods of reduced NADW formation, eventually surface waters at key sites of deep-water formation would become salty and dense enough again to sink, thus restarting AMOC and causing an abrupt warming in the high-latitude North Atlantic, triggering the warm phase of a D-O cycle.


Figure 27. Mechanism of the salt oscillator hypothesis. (a) During warm interstadials, when AMOC is stronger, enhanced northward oceanic heat transport results in warmer conditions in the North Atlantic. Warmer conditions in the North Atlantic cause the ice sheets around the North Atlantic to melt, gradually reducing surface water salinity. Eventually, surface salinity is reduced enough to weaken AMOC, shifting the climate into a cold stadial. (b) During stadials, cooler conditions in the North Atlantic reduce meltwater input from the ice sheets, allowing an increase in surface salinity that eventually causes AMOC to strengthen, returning the climate system to an interstadial. Source: Schmidt, M.W. and Hertzberg, J.E. 2011. Nature Education Knowledge 3 (10):11. (c) Atlantic profile from 30°S to 90°N showing the underwater crest between Greenland and Scotland. Interstadial conditions show a strong AMOC capable of crossing the crest. Stadial conditions show a weakened AMOC that turns further South. During Heinrich events the AMOC collapses. Source: Rahmstorf, S. 2002. Nature 419 207-214. AMOC: Atlantic Meridional Overturning Current. NAC: North Atlantic Current. NADW: North Atlantic Deep Water. AABC: Antarctic Bottom Water.

Several studies have suggested that it only takes a small reduction in sea surface salinity to alter the rate of NADW formation, to the point that some scientists, including late Wallace Broecker and Richard Alley became worried that an increase in the hydrological cycle due to current global warming could reduce North Atlantic salinity, leading to the shut down of the AMOC causing an abrupt cooling in the near future (Broecker, 1999). They seem to forget that before the mid-Holocene transition, around 5000 yr BP, the northern Atlantic region was warmer and generally wetter than present, when the Sahara was a savanna type of environment, and the AMOC did not shut down.

The salt oscillator hypothesis does not provide a specific explanation for the regular 1470-year pacing of D-O cycles. The pacing must come from intrinsic delays in the salinity and meltwater build up and depletion and the response to these processes by the ocean currents very much like the pacing of a pendulum depends on its length, but climate variability does not have the regularity of simple physics.

In recent years, this consensus view of D-O cycle formation through salinity-oscillation has come under assault on several fronts. While several studies have questioned the occurrence of MWP at the expected time intervals, others indicate that AMOC is a lot more stable than required by the theory and even extreme MWP would not be able to destabilize it sustainedly.

The work of Rasmussen and Thomsen (2004), also confirmed by Dokken et al. (2013), and Ezat et al. (2015), and theoretically framed by Petersen et al. (2013; see Climate Etc. article) shows that during stadials the flux of warm water to the North Atlantic and Norwegian sea does not cease. Instead during cold stadials warm waters enter the Arctic under the sea ice and thus instead of ceding the heat to the atmosphere, they warm the subsurface waters below an insulating cold water layer made of fresh superficial water and a cold and saline halocline. Thus while the atmosphere gets colder and sea ice increases, the ocean heat accumulates at the subsurface level, and no cold bottom water is produced.

Mechanistic explanation of the Dansgaard-Oeschger cycle

According to available evidence and new theories, and starting the cycle at the point during the stadial when Antarctica starts warming, the bipolar see-saw is set to warm Antarctica and cool the north polar regions. At that point, the AMOC is weakened and transmits less heat towards the North Atlantic. As the North Atlantic and the Arctic cool down, ice sheets expand and sea-ice increases reaching farther South (figure 28a).

As Antarctica gets warmer and the Arctic colder, the amount of warm water transmitted North starts to increase due to the enhanced equator-polar thermal gradient. This warm water produces an enhanced iceberg discharge that carries IRD to the ocean sediments, but the warm water fails to warm the higher latitudes because instead of venting the heat to the atmosphere it submerges below the ice sea where it gets layered and insulated by the halocline (figure 28b).

Every ~ 6,000 years Antarctic warming and Arctic cooling are enhanced and prolonged. The temperature gradient increases and more warm water gets moved North, where more ice has built up, so the iceberg discharge is much higher, producing a Heinrich event (figure 28d).


Figure 28. Mechanism of the D-O cycle. (a) At the beginning of the stadial the Arctic is cooling down, sea ice is growing, and surface warm water (orange) is reduced. (b) At the end of the stadial the Arctic cooling is maximal, Antarctica is warming, and there is an increase in the warm North Atlantic Current, that produces an increase in iceberg discharge carrying ice-rafted debris (IRD). At the Norwegian sea, warm waters sink below the ice preventing warming. From time to time these conditions are enhanced to produce a Heinrich event. (c) An interstadial is abruptly produced when in an explosive manner the warm water rises and melts the sea ice, transferring heat to the atmosphere. Source: Raj Saha (d) Conditions during a Heinrich event as modeled. Observe the North Atlantic cooling. (e) Conditions during a D-O abrupt warming as modeled. Source: Ganopolski, A. and Rahmstorf, S. Nature 409 153-158.

Every 1470 (± 120) years the subsurface warm waters at high North latitudes rise to the surface and abruptly warm the atmosphere (figure 28c, e), starting the Greenland interstadial. This warming inverts the bipolar see-saw, so the Antarctic region starts to cool after about 200 years. As warm waters cool down they sink and form the NADW, so the higher northern latitudes start to cool. Once sea ice regrows and the halocline forms, it insulates the warm waters from the atmosphere and the temperature drops putting an end to the interstadial. The deep cooling of the new stadial flips the bipolar see-saw restarting the cycle.

There is evidence from Norwegian sea sediments, that have preserved the temperature record of the sea, that changes in sea temperature and stratification precede the abrupt atmospheric changes (Dokken et al., 2013). During the stadial phase, the planktonic foraminifera record the temperature of cold water within, or just below, the halocline. As the stadial phase progresses, the planktonic foraminifera show an increase in temperature (Figure 29) consistent with the continuous arrival of relatively warm and saline Atlantic water below the halocline. With no possibility of venting heat to the atmosphere due to the sea ice cover, the decrease of subsurface water density weakens the stratification that allows the halocline and sea ice cover to exist. The transition to a warm Greenland interstadial occurs when the stratification collapses, at which point heat from the subsurface layer moves rapidly to the surface, melting the sea ice cover (figure 30). This sudden mixing of warm and cold water is seen in the planktonic foraminifera proxy record as an abrupt sea temperature warming that precedes the atmospheric warming (figure 29).


Figure 29. Subsurface temperature in the Norwegian sea. Proxy temperature records covering the period 41 to 31 kyr BP. Top panel in blue, NGRIP δ18O proxy for Greenland temperature. Bottom panel in red, sea surface reconstructed temperature (SST) based on planktonic foraminifera assemblages. Source: T.M. Dokken et al. 2013. Paleoceanography 28 491-502.


Figure 30. Norwegian sea vertical reorganization model. Schematic showing wintertime conditions in the North Atlantic and Norwegian sea during typical (left) cold stadial periods and (right) warm interstadial periods of a D-O cycle. Locations A and C show north-south sections of the North Atlantic during stadial and interstadial conditions, respectively. Locations B and D show east-west sections of the Norwegian Sea during stadial and interstadial conditions, respectively. During stadial periods warm northward Atlantic water is stratified below insulating layers of sea ice, cold fresh water and cold saltier water (A and B). At interstadial periods the stratification collapses and the warm Atlantic water reaches the surface warming the atmosphere (C and D). Source: T.M. Dokken et al. 2013. Paleoceanography 28 491-502.

Lunisolar tidal cycles as an explanation for Dansgaard-Oeschger triggering mechanism

The cause for the observed 1470-year periodicity is one of the great mysteries of paleoclimatology. Proposed explanations fall into two classes: internal variability, like oscillations in ocean circulation or ice sheet dynamics, and external forcings, like variations in the sun or orbital planetary cycles. But each explanation has shortcomings. Internal variability hypotheses have a problem explaining how such precise periodicity can be achieved given the great intrinsic variability of the involved phenomena and given the large variability in the duration of D-O oscillations (figures 11 and 14). Solar cycles of ~1500 years are unknown. Orbital cycles of ~1500 years are not widely accepted and the closest known lunar cycle has ~1800 years.

I have looked at most explanations for the highly regular pacing of the D-O cycle and they all come quite short. Internal factors like changes in oceanic currents or ice build up are influenced by too many variable factors like wind and temperatures to expect that they are capable of producing such regularity. The same goes for the vertical reorganization of stratified Norwegian sea waters. During Heinrich events the time and amount of subsurface warm water build up is much higher, yet the pacing is maintained. Regarding external factors, the Sun looks problematic. There’s no ~1,500-year solar cycle signature in the proxy records and changes in solar luminosity are not precise (the sunspot cycle shows a 14% variability in pacing), nor intense enough to explain the observed changes.

There are very few scientists defending a tidal origin to the pacing of D-O cycles, and curiously, Charles Keeling, the father of global CO2 measurements since 1956 at Mauna Loa, dedicated his later years trying to find a tidal origin to temperature changes (Keeling and Whorf, 1997; 2000). Yet as outlandish as the tidal hypothesis sounds initially, it is uniquely capable of explaining some of the mechanistic features of the D-O cycle available evidence.

As with any suspected cause, we have to ascertain that it has the means and the opportunity. Are tides capable of producing the required effect? Regular tides already have a strong effect in ocean water vertical mixing. The vertical mixing effect of tides is calculated annually at 4 terawatts, versus 2 TW for the wind (Keeling and Whorf, 1997). Since ocean waters are temperature stratified, vertical mixing is one of the main factors in ocean temperature changes. Moreover, tides also take place below sea ice, where they are the only factor affecting vertical mixing.

Tides also increase their power in a non-linear way in cycles, the main one being the 18.6-year nodal cycle. Since the orbit of the Moon has an inclination of ~5° with respect to the orbit of the Earth, the nodes are the points at which the Moon crosses the ecliptic plane, and the line that joins both nodes produces a full rotation every 18.6 years. This produces alignment cycles with different periodicities. These occur when the Earth is at perigee and the Moon is at apogee or perigee at the same time the Moon crosses the ecliptic, and when the Earth, Moon and Sun are in syzygy. Even more important than these alignment cycles, tidal strength varies with harmonic beats of tidal frequencies at longer cycles. These cycles act on a centennial scale and unlike the alignment cycles produce very high tides over a period of months or years. They have been associated with cool periods of historic times (Keeling and Whorf, 1997; figure 31).



Figure 31. Timing of lunisolar tidal forcing from A.D. 1600. Each event, shown by a vertical line, gives a measure of the forcing in terms of the angular velocity of the moon, in arc degrees per day, at the time of the event. Arcs connect events of each prominent 18.03-year tidal sequence. Also plotted are times of cool episodes seen in climate data. Centennial maxima are labeled with letters. Climactic events of the dominant sequences from 1700 and 1974 are at about 90-year intervals. Source: C.D. Keeling and T.P. Whorf, 2000. PNAS 97 3814-3819.

The strongest dominant tidal sequence of the last 200 years took place on January, 8th, 1974 (figure 31). Therefore we can check if anything unusual happened with tides around that date. According to historical records unusually high tides affected the western coasts of US and Europe in January of 1974. In Western Europe the tides coupled with storms caused severe flooding in Ireland, where the severity of the damage on the 11-12th January flooding was higher than a previous hurricane “Debbie”, causing the worst disaster in history for the Electricity Supply Board of Ireland (Keane and Sheahan, 1974).

In the US, Fergus Wood, a researcher for the National Oceanic and Atmospheric Administration (NOAA), gave a public warning on December 26, 1973, on the upcoming very close perigee-syzygy alignment of January 8, 1974, and coastal damage was prevented by sandbagging, backfilling, and other precautionary measures. The Los Angeles Times reported on Wed., Jan. 9, 1974 (CC Ed. Part I, Page 1, Cols. 2, 3) “Giant waves pound Southland coast, undermine beach homes. Sandbag barriers erected to ward off tidal assault.” (Wood, 1978). The next alignment on February 9 also caused a tidal flooding along the southern coast of England.

In Fort Denison, at Sidney Harbour, Australia, analysis of water levels since 1914 to 2009 show that the largest tidal anomaly was recorded on 26 May 1974 during the most significant oceanic storm event on the historical record. Over this timeframe some 96.8% of the measured anomalies fall within the bandwidth between -10 cm and +20 cm. The anomaly of 1974 measured 59 cm (Watson and Frazer, 2009).

Ocean tides beneath the Ross Ice Shelf in Antarctica were measured between December 1973 and February 1974 by Robinson et al. (1974), where they detected tides of about 2 meters underneath the ice shelf by gravimetry.

So it is clear that unusually strong tides take place with centennial periodicities capable of exerting powerful vertical mixing even below sea ice, thus providing a mechanism for triggering a Dansgaard-Oeschger abrupt interstadial warming. Tides were already demonstrated to enhance iceberg calving by Otto Petterssen in 1914, but tides are also sensitive to sea levels and so some researchers have found, through models that reproduce current tides, that with glacial conditions of low sea level, much bigger tides would be produced in certain areas of the world (Arbic et al., 2004; Griffiths and Peltier, 2008). These areas are located mainly in the North Atlantic region (figure 32), so the authors propose a tidal origin for Heinrich events. As tidal waves propagate, these mega tides of the glacial period would have affected the North Atlantic – Norwegian sea area where D-O cycle’s abrupt warming take place.


Figure 32. Ice age tidal amplitude. Tidal amplitude (m) of the principal lunar semidiurnal tide M2 at (a) present time and (b) 23 kyr BP in a hydro- dynamical model coupled to a gravitationally self-consistent (hence geographically variable) prediction of sea-level change. Between the areas with stronger tides are those producing iceberg discharges during Heinrich events (HE, black circle), and Norwegian sea area where D-O abrupt warming originates (dark blue circle). Source: S.D. Griffiths and W.R. Peltier. 2008. Geophys. Res. Let. 35 L08605.

We have seen that lunisolar tidal cycles have the capability to produce mega-tides during the glacial period, strong enough to produce intense vertical water mixing, and thus capable of explaining the triggering of D-O cycles. The tidal hypothesis is very consistent with the known requirements for D-O cycles: cold conditions that favor extensive sea-ice cover, water temperature stratification with enough density differential, and sea level low enough for huge tides to be produced, but not so low that the ice cover is too thick and stable.

The tidal hypothesis appears to have the means, does it have the opportunity? No clear 1470-year tidal cycle is known from the data, however one can be deduced from the theory. We have already seen that the nodal precession takes place every 18.6 years. The apsidal precession, or perigee cycle is the rotation of the elliptic orbit of the Moon around the Earth every 8.85 years. By the time a nodal cycle takes place (18.6 years), two perigee cycles occur (17.7 years). These numbers are so close, that both cycles produce maximal interference every 366 years, at which point bigger tides take place. Berger et al. (2002) have proposed that the cycle of 1470 years results as a factor of 4 over the 366 years harmonic beat reflecting, perhaps, the requirement that maximum tidal action occurs in a relatively narrow window during the summer season, when the sea ice is most susceptible to disruption by tides.

A lunisolar tidal cycle of millennial scale is just a hypothesis for the 1470-year pacing of the abrupt D-O cycle warming without supporting evidence. During the Holocene the D-O cycle disappears, because it requires low sea level, extensive sea ice and inverted temperature stratified waters, with the possible participation of enhanced glacial tides. However, as we will see in a future article of this series, an echo of an oceanic signal with the same periodicity resonates over the Late Holocene (Neoglacial) climate. The general features of this signal also agree well with what could be expected from a lunisolar tidal cycle during a warm interglacial: increased storminess and decreased sea-surface temperatures.


1) Between 90 and 12 thousand years ago, Greenland proxy temperature records show more than 20 abrupt and intense climatic changes, known as Dansgaard-Oeschger events, paced according to a 1470-year periodicity.

2) Each D-O oscillation is preceded by North Atlantic cooling and iceberg discharges that, when intense and prolonged, constitute a Heinrich event.

3) D-O oscillations present an asymmetric change in temperatures with warming of 8-10°C in a few decades followed by a cooling in stages lasting from a few centuries to over a millennium.

4) Prior to abrupt warming in Greenland, temperatures rise in Antarctica until about 220 years after the start of Greenland warming.

5) The abrupt northern hemisphere warming increases global methane concentrations from boreal wetlands due to increased temperature and precipitations.

6) CO2 has no role during D-O cycle, and its levels are neither cause nor consequence of the most frequent and most abrupt climate changes of the past. The increase in CO2 levels during Heinrich events does not significantly alter the rate or magnitude of the warming during the subsequent D-O oscillation.

7) D-O oscillations require sea levels between 45 and 90 m below present, and appear to be inhibited by maximal obliquity.

8) The leading theory, the “salt oscillator hypothesis,” does not explain the periodicity and relies on unproven melt water pulses and a shut down of the Atlantic Meridional Overturning Current unsupported by evidence.

9) Rival D-O theory proposes the stratification of warm subsurface waters below the halocline and the sea ice in the North Atlantic and Norwegian sea, with the abrupt warming taking place due to the collapse of this stratification and the melting of the overlying ice.

10) A lunisolar tidal cycle provides an unsupported hypothesis that explains all of the known evidence for the 1470-year pacing and the triggering mechanism for D-O oscillations.

[ references ]


I thank Andy May for reading the manuscript and improving its English.

Moderation note:  As with all guest posts, please keep your comments civil and relevant.

226 responses to “Nature Unbound II: The Dansgaard- Oeschger Cycle

  1. Pingback: Nature Unbound II: The Dansgaard- Oeschger Cycle – Enjeux énergies et environnement

  2. During the cold part of a major ice age, the ice sheets are extended into climates with more sunshine. The melt rates are the most in the coldest times because the exposure is the most. Ice melts and collects as ice extent is still increasing. The sudden events are caused by some of the collected water breaking out to warmer places, warming more in the sun, then evaporating and returning to land as more ice. I have been waiting for someone else to notice these events and discuss them. The overall cold ended when the major ice sheets ran out of enough ice to continue these cycles.

  3. Javier

    interesting stuff that will take me a few reads to get my head around.

    you say

    ‘…abrupt and intense climatic changes, known as Dansgaard-Oeschger events, paced according to a 1470-year periodicity….’

    I didn’t see the answer in your text but when is the next event due if this 1470 periodicity holds up? In other words, when was the last known one?


    • The last sudden cooling and warming event occurred between 20 and 10 thousand years ago when the water dumps from melted ice sheets used the last of the stored water and dumped it into the oceans for the last cold water dump that caused the last sudden cold period, just before the last recovery into the last really major sudden warming. We are done with that because we do not have any more large melt water lakes that are in danger of breaking out.

    • Hi Tony,

      The last sudden warming that can be identified as a D-O event is the warming that took place right when the Younger Dryas ends, 11,700 years ago.

      D-O events can only take place during glacial periods, but during the Holocene there is the possibility that the D-O cycle has transformed into the 1500 year oceanic cycle. If this hypothesis is correct, and it is supported by some evidence, then the last occurrence took place during the Little Ice Age. I will explain it better when we get to the article about the 1500 year oceanic cycle.

  4. My research on DO events agrees with . that CO2 has no role and the role of the halocline and the accumulation of subsurface heat that eventually melts insulating ice ventilating large amounts of heat. I called it the Arctic Iris Effect. Changes in the volume of transport of warm Atlantic waters into the Arctic would also play a role. The modern changes in Arctic sea ice are based on the same mechanisms as the DO events and explains the warm peaks in the 30s and today.

    Read How Much Does the Arctic Iris Effect Explain Recent Warming, 1930s Warming and Dansgaard-Oeschger Events?

    • Hi Jim,

      Your article is very interesting. It makes sense that the Arctic sea ice cycles are based on the same mechanisms, as they should operate all the time proportionally only to the heat transport that is determined by the equator-polar gradient.

      I agree that the next two decades are going to be very important to work out the contributions to global warming by natural and anthropogenic causes. There are several skeptic hypothesis pointing out to a change of cycle, including the Stadium Wave hypothesis of Wyatt & Curry.

    • Jim Steele,

      Can you comment on causes of the 150 Ma cycle of coldhouse phases and 300 Ma cycle of deep coldhouse phases? See my question to Javier in comment here:

      • Peter I dont know enough about those ancient climates but I suspect that the changes between hothouse and ice house were largely driven by continental configuration. I described a possible mechanism for the recent 60 million year cooling trend in an essay the Antarctic refrigeration effect. I would speculate that the same mechanism would cause an oscillation between hothouse and ice house climates

        If a continent is situated over the pole plus a circumpolar current can be established, then the polar region can become insulated enough from transported tropical waters to allow freezing. The poles naturally radiate more heat than they absorb, so without heat transport , sea ice forms in the winter. Due to brine rejection the oceans begin to cool from the bottom up. As colder water volume increases and shoals it begins to upwell and cools the planet. This is consistent wit Antarctica’s ic cap forming first and then 30 million years later the Arctic ice cap forms

        When the continents are aligned in a more continuous north south configuation meridonal heat transport is encouraged. Enough heat reaches the polar regions to prevent sea ice formation. Now the deep waters can only be filled by densest salty waters formed by evaporation, and the ocean depths begin to warm, and as the warm volumes increases, warmer upwelled water smove the climate more to a hothouse.

        I dont know enough detail regards the continental paleo-configurations as Gondwana sutured together and then split up, but some animations suggest there could periods enhancing high transport of tropical heat and periods of isolated continents as Antarctic is now, promoting sea ice and deep cooling

      • Jim Steele,

        Thank you very much for that clear explanation. What you explain in your comment is consistent with what I understand from others. I’ll read your paper tonight with interest.

        Have you seen Plate Tectonics and Climate Change ? It was provided to me by a researcher at Geoscience Australia recently. Pages 6 to 8 Ocean Gateways interested me.

        Readers may be interested in this 3:39 tectonic plate animation by Scotese. It shows where the tectonic plates were going backwards in time in 10 Ma steps to 750 Ma ago – i.e., before complex life (animals) began.

    • Interesting in this regard that Antarctica led the way out of the last glacial period. Also very interesting that methane, and not CO2, is extremely sensitive to DO events.

  5. Andy May ==> Great editing job — it makes a world of difference that an important essay or journal article read properly in English (if it is to be published in that language). We have all experienced reading manuals for even very expensive technical equipment that has obviously been written by a non-native English speaker — and like it or not, fair or not, it can shake our confidence in the product.

    My editor (Vassar, English and French and Philosophy, ΦΒΚ) keeps me straight when I let her.

  6. And they say there is no God…

    Ocean and lake sediment data from places such as California, Venezuela, and Antarctica have confirmed that these sudden climate changes affected not just Greenland, but the entire world. During the past 110,000 years, there have been at least 20 such abrupt climate changes. Only one period of stable climate has existed during the past 110,000 years–the 11,000 years of modern climate (the “Holocene” era). “Normal” climate for Earth is the climate of sudden extreme jumps–like a light switch flicking on and off.

    See: NOAA | Lesson Plan: Climate Change and Current–Grade Level: 9–12; Subject Area: Earth Science |

  7. Possible something from well outside the solar system periodically swings inward and kicks-off perturbations? Just a thought.

  8. Javier
    One of the positives about AGW theory, is that is has emphasised the need for diverse and intense research on the subject in a short period of time, and the REAL effects of assumed GH gases.

    A thorough article and a great contribution.

  9. If anybody is interested in the previous article of this cycle, about the glacial cycle, it can be found at:

    or in PDF format it can be downloaded from:

  10. Impressively detailed speculation, but wrong. The Earth’s surface was re-formed, wholesale and late in geological history, to a great design:

    “Challenge to Earth Scientists”, and

    “Challenge to Science II: Focus on Design”.

    In fact, the entire solar system was re-formed, and reoriented to follow the Earth’s new (present) orbit:

    “Challenge to Science III: The ‘gods’, the design, and man”.

    The continents were deliberately moved, shaped and oriented. Some were moved as late as 10,000 years ago, along paths that are today thought to be spreading ocean ridges. They are instead the sutured scars of past movement of landmasses like Atlantis/Greenland (just one of the most famous ancient mysteries, originating in the design, solved by my research):

    “Atlantis At Last”, and

    “Atlantis Details”.

    The Earth’s–and solar system’s–new orbital orientation was effected c. 17,000 years ago (as mentioned in “Challenge to Science III”, above link). Plato’s “Timaeus” reported that the Egyptians dated the disappearance of Atlantis to 9600 BC, indicating the change to the present distribution of landmasses was performed over several thousand years’ time, between roughly 20,000 and 10,000 years ago.

    Modern geology (including paleoclimatology, e.g. ice core data) cannot be trusted any farther back in time than the end of that deliberate re-formation, by the ‘gods’, who were worshipped by ancient man worldwide. That worship directed the religions and religious obsessions of man for thousands of years, as observed in the perennially-popular “ancient mysteries”, all of which hark back, in precise detail, to that single source, the deliberate world design.

    The Fig. 18 in the above article notes that the periodicity in the DO cycle has less than 1% probability of being due to chance. Compare that to the probability of chance placement of the continents in their current, precisely-set form and distribution, which is on the order of 1 in one million million (1 in 1 trillion). What I have just informed you of is so far beyond the “certainty” of modern scientific speculations like the article above, that to dismiss it is logically perverse, in the extreme. The great design makes practically all that current earth scientists think they know, immediately irrelevant to the truth, and useless to continue with or build upon. It literally sweeps away, effortlessly, the underlying assumption–no design involved–in both evolution and plate tectonics, the central theories of all the life and earth sciences. They are wrong; everything proceeding on the basis of their truth is wrong.

  11. [Repost at correct level]


    O/T for this thread, but can you suggest a link to an, authoritative, widely-accepted, short, succinct, clear (for non-experts) explanation of the cause of the ~300 Ma cycle of coldhouse phases, as shown on Scotese (2016) Figure 15:


  12. Pingback: Bits and Pieces – 20170218, Saturday | thePOOG

  13. Wow
    What a comprehensive study. Thanks.

  14. “They all display a very fast warming, with temperatures rising by about 8-10°C in just a few decades, within the span of a human life time”

    That”s interesting.
    Were there mass extinctions?

    • Isn’t that the real question? If you could plot the planet’s biomass and species abundance/diversity over the same time periods it would have some relevance to ultimate question… are 7-10 billion humans having a bigger impact than this background variability?

      • Jack, the biosphere is more productive in warm periods than in cold periods.

        Life thrives in warm periods and struggles in cold periods IPCC AR4 WG1) says :

        There is evidence that terrestrial carbon storage was reduced during the LGM compared to today. […] a reduction in the terrestrial biosphere carbon inventory (soil and living vegetation) of about 300 to 700 GtC (Shackleton, 1977; Bird et al., 1994) compared to the pre-industrial inventory of about 3,000 GtC.

        That is 80% to 90% less terrestrial carbon storage at the LGM compared to today

      • Yes, jacksmith4tx,

        The human impact on wildlife biomass and extinction is likely to be much higher than the effect of climate changes over the past 50,000 years.

        Barnosky, A. D. (2008). Megafauna biomass tradeoff as a driver of Quaternary and future extinctions. Proceedings of the National Academy of Sciences, 105(Supplement 1), 11543-11548.

      • Javier,
        That was a excellent reference. I agree with the projections they make just based on the energy flows they calculate. Of course there are so many human controlled variables at play excluding CO2, changing chemical compositions of different parts of the biosphere, genetic engineering not to mention nuclear war. Maybe AI will save us by clearly quantifying where the truth and risks are in our future. If someday we create a AI program that tells us how to avoid the worse outcomes will we listen?

    • These are perhaps regional rather than global.

    • Rebelronin,

      As Barnosky describes it:
      “The Quaternary Megafauna Extinction (QME) killed >178 species of the world’s largest mammals, those weighing at least 44 kg (roughly the size of sheep to elephants). More than 101 genera perished. Beginning ≈50,000 years (kyr) B.P. and largely completed by 7 kyr B.P.”

      I was not a mass extinction by far. Mass extinctions implicate the extinction of 75% of genres whether at land and/or marine ecosystems.

      Scientists are split between those that believe the QME had natural causes or anthropogenic causes. In general defenders of anthropogenic climate change defend the opposite for QME. However in the case of Australian extinctions it has been shown quiet conclusively that the arrival of humans coincided very narrowly with its trigger. Occam’s razor states the economy of causes, so the same explanation for the QME is likely, even if some species went extinct for different reasons.

  15. Javier, excellent work and very interesting and thought stimulating ideas. I have recently read that the ENSO may be related to tidal induced sloshing of the Pacific Ocean:


      Over the Holocene – immense variability is evident in a high-resolution sediment record. Christopher Moy and colleagues examined a sediment core from Laguna Pallcacocha in southern Ecuador. More rainfall and runoff from a warmer sea surface in the eastern Pacific washes more red sediment into the lake. So we know it was pretty rainy in South America a 1000 years ago. Some 5,000 years ago there was a change from more upwelling to less – that dried the Sahel. Just 3,500 years ago there were a long series of cool Pacific events with red intensity greater than 200 and civilisations fell. For comparison – red intensity in the ‘monster’ 1997/1998 El Niño event was 99. Extremes in the Holocene put those of the 20th century to shame. There is a 2000 year pattern.

      There are coherent changes in Pacific upwelling that go beyond any possibility of an internally resonant cause.

    • Hi oz4caster,

      That meeting abstract is by Paul Pukite, a.k.a. WebHubTelescope, who hasn’t been able to publish it since 2010 when he sent it to its first journal. I am not able to judge its merits, nor do I want to expend time on unpublished research, so I reserve judgement until he gets it published if he ever does. WebHubTelescope used to post here until he was banned. Despite being unpublished in climate research he is very vocal about being smarter and more knowledgeable than every skeptic climatologist, including Lindzen and Curry.

  16. I appreciate your work Javier. Well done on a thoughtful post.

    “Now imagine that you have never seen the device and that it is hidden in a box in a dark room. You have no knowledge of the hand that occasionally sets things in motion, and you are trying to figure out the system’s behavior on the basis of some old 78-rpm recordings of the muffled sounds made by the device. Plus, the recordings are badly scratched, so some of what was recorded is lost or garbled beyond recognition. If you can imagine this, you have some appreciation of the difficulties of paleoclimate research and of predicting the results of abrupt changes in the climate system.” NAS (2002) Committee on Abrupt Climate Change

    Of course the further back in time we go – the more difficult it is to take it seriously. In the Holocene the equivalent cycle is ice rafting in the Atlantic – Bond Events.

    it is associated with the production of cosmogenic isotopes – implying a solar origin.

    We can see similar periodicities in ENSO – in this high-resolution proxy shown in a comment above.

    Including the mid-Holocene transition that is the proximate cause of Sahel drying. How to connect it all is with the well-established link between solar UV and ozone that results in changes in sea level pressure at the poles. Low solar activity pushes storms into lower latitudes and spin up all of the ocean gyres. In the Pacific this facilitates fridig and nutrient rich upwelling from the deep ocean. At the peak there is cold water over an immense area of the Pacific – associated with more cloud, a cooler planet, huge changes in global hydrology and biological abundance.

    It is part of a globally resonant system – but it is a big part.

  17. And we have a new theory for glacial (stadial) initiation.

    ‘Lee’s models show that, aided by high eccentricity, cool Southern Hemisphere summers can decrease by as much as 17 percent the amount of summer solar radiation absorbed by the planet over the latitude where the difference in sea ice distribution is largest — enough to cause significant global cooling and potentially creating the right conditions for an ice age.”

    • Robert,

      Glacial inception is clearly a matter of obliquity. Falling obliquity has never failed to bring a glacial period. It comes with a variable delay that on average is 6,500 years, due to the thermal inertia of the planet, the same inertia that explains why the coldest part of the winter is by late January-early February, when minimal insolation is at the winter solstice.

    • As the article says – precession is involved as is orbital eccentricity. What they did explore is a physical mechanism involving Antarctic sea ice.

      • Robert,

        The article you link is wrong because paleo-climatologists have erred their way trying to explain a 100 Kyr cycle that does not exist. It is an artifact of the data.

        “The 100,000-year pace of glacial-interglacial periods has been difficult to explain,” said Jung-Eun Lee

        Of course, because it doesn’t exist. It comes from an incorrect definition of interglacials and a spurious mathematical averaging of interglacial distances. This was thoroughly discussed in the previous article of this series, including this figure:

        When you account for the irregularities of MIS 11 (a long interglacial) and MIS 7e (a short interglacial), the spacing of every interglacial falls squarely on the obliquity cycle (bringing MIS 11 and MIS 7e to their correct distance also adjust the next dots, MIS 9 and 7c, to the obliquity cycle distance).

        Precession and eccentricity are important for deciding if there is going to be an interglacial when obliquity rises. For glacial inception (interglacial termination) the only relevant factor is falling obliquity.

        As many others before them, the authors of the study that you link are mistaking effect for cause.

      • The effect is clearly there with interglacials every 100,000 odd years – and the cause is ice sheet feedback triggered by small changes in insolation.×200.png

  18. Javier, thanks for such a comprehensive and very readable article. I can see I’ll need to read it several more times to fully take it all in and I will await the next article with interest.

  19. I – am – Nay-chur. ( Flashes of lightning,
    clashes of thunder.) It – is – true,
    (puny humans) that you who
    live on the littoral), dependent on
    my bounty and my whim) think you
    are master of all you survey, hey,
    think again, (puny humans) hubris
    has its consequences, do not rely
    on some 97 per cent con-sen-suss,
    re modelling or cherry-pick-shenanigans,
    (tampering with tree ring samples ‘n such
    (Cymbal crashes in lieu of thunder) …
    Nay-chur – has -its – way.

  20. ‘Orbital cycles of ~1500 years are not widely accepted’

    It’s 74 Jupiter-Saturn conjunctions = 41 Saturn-Neptune = 115 Jupiter-Neptune (115 = 74 + 41). The period for this triple alignment is 1470 years.

    It’s about 123.92 Jupiter orbits, 49.92 Saturn, and 8.92 Neptune.
    (The difference between those numbers = the number of conjunctions).
    Planetary data:

    • Yes Oldbrew, I did not say they do not exist. One can essentially find an orbital cycle for almost any number. And that is the problem. That is why they are not widely accepted as causal to climate changes. There is no known mechanism and only a temporal coincidence with one of the many planetary dances.

      • Sorry but I disagree. Three-planet harmonics are few and far between.

      • I don’t know about that, but I know that besides this planetary harmonic for the 1470 year D-O cycle, we also have Charvatova’s 2402 year trefoils for the ~ 2400 year Bray solar cycle, or the Venus–Earth–Jupiter spin–orbit coupling model of Wilson:

        “the 1156.3 yr is most likely just a multiple of the fundamental Jupiter re-synchronization period of 575.518 yr.
        These multiples of the 575.518yr Jupiter re- synchronization cycle include:
        2 × 575.518 = 1151.0 yr 3 × 575.518 = 1726.5 yr 4 × 575.518 = 2302.1 yr − Hallstatt cycle.”

        Another planetary explanation with multiple numbers to nearly fit several cycles.

        There are multiple variations of the planetary theory, Scafetta’s, Abreu’s planetary torque, Sharp’s. Since all of them appear to explain climate change the conclusion is that none of them does. That type of research is fruitless in my opinion. It has a long story since Wolff and Jose, but it hasn’t got anywhere.

      • You’re telling me there’s no known mechanism in response to being offered one?

        Note that the Saturn-Neptune conjunction number is 41 which is a prime number.

      • I am not being offered a mechanism. I am being offered a pre-selected cosmic coincidence.

        The only known mechanism by which the planets of the Solar System affect the climate of the Earth is through the alterations of the Earth’s orbit already described in detail by Milutin Milankovitch.

    • These are not orbital cycles – but solar variability that can be tracked in isotopes. Planetary motions may have something to do with the solar magneto – but also fluid dynamics within the sin itself.

  21. Pingback: Nature Unbound II: The Dansgaard- Oeschger Cycle | privateclientweb

  22. The article seems to dismiss the possibility of a new meltwater pulse from the current warming, based on the idea that the mid-Holocene (5000 or so years ago) had similar temperatures to now. This forgets that sea levels then were likely a few meters higher, temperatures are rising a few more degrees yet in this century, and there is enough ice in Greenland to form a pulse of a few meters sea-level rise that would be the definition of a MWP episode, shutting down the AMOC and cooling Europe significantly. This is a scenario recently published by Hansen. Meltwater pulses have occurred countless times in the paleo record, and our current highly-forced polar warming situation pushes hard at this type of tipping point for the remaining glaciers.

    • jimd said

      ‘The article seems to dismiss the possibility of a new meltwater pulse from the current warming, based on the idea that the mid-Holocene (5000 or so years ago) had similar temperatures to now. This forgets that sea levels then were likely a few meters higher….’

      I am glad you are agreeing with what we have been saying to you for years about sea levels. Todays are by no means unusual

      We can accurately trace previous water levels for both river and sea by following the romans and saxons and Vikings in Britain. I would estimate that for the Vikings to pillage so far up European river systems and for King Alfred to hide in the somerset levels, that water levels were at least 1 or 2 meres higher as recently as 1000 years ago,

      do you know of any estimate that would tell us what the rise in sea level would be for each 1 degree centigrade rise in temperature?


      • The current warming means that sea levels are below the value they should be for the current temperature by maybe several meters. There is some catching up to do and it is the glaciers that are behind on their melting, hence the meltwater pulse that is due, which has consequences on AMOC and hence European temperatures. If there’s two things that grab the attention of even the skeptics, they are rapid sea-level rise, and more severe winters. Meltwater pulses are the perfect storm in that sense. As to your question, at even 4 C higher, both the polar glaciers would be on borrowed time, leading to eventual rises of tens of meters at rates of many meters per century.

      • In order to be a meltwater pulse it will be necessary for there to be an energy pulse.

        Where do you expect that to suddenly appear from?

      • This has occurred so often in the past with very subtle forcing changes, especially during the exit from the last Ice Age.

      • Wrong, as usual.

        The “pulse” during the exit from the last ice age was due to the collapse of a huge moraine dam that permitted a volume of cold gresh water of approximately a third of the volume of the north Atlantic to be released in a period of a few months.

      • You can check as well as I can that the suspected origins of some major meltwater pulses was the Antarctic.

      • Tony,

        You have to adjust for the lost of river flux due to increasing water usage. The Colorado river no longer reaches the ocean, and that is not due to falling sea levels.

        Near East rivers are now a pale shadow of their former, but not due to decreasing precipitations as some alarmists fear, but due to sustaining a multi-million population and their water usage.

      • Javier

        That may be so for some rivers but obviously isn’t so for sea levels..

        Even then the river situation is complicated as reduced heavy industry requiring vast amounts of water for their industrial processes means many rivers once again have a healthy flow.

        Ground water levels in London have been rising for decades as industry leaves.


      • tonyb
        that is so interesting about ground water levels in London.

        All over the US they are depleting. Causes the land to sink and thus relative sea level to rise. Don’t tell JIm D. It is a secret of science.

        In lower San Juaquin basin down 35 feet or so.

        In San Diego the terraces above and below the existing sea level show a range of 100 meters higher and three hundred meters lower. I am speaking from memory and have to go look but Dogger land in the North Sea and the shores of Berring straight land bridge between asia and north america demonstrate the wide range of levels. Farallon islands are 26 miles of the coast of San Francisco and used to be walkable from the Golden Gate.

        The Sea is Rising!!

        The Sky is Falling!!

        How is the study of sea levels II from the Roman times to 1700 coming?

      • Scott

        I have been doing some preliminary research in advance of part two. It will likely centre on the higher than today water levels in the medieval period. The deep rivers enabled the Vikings to sail well inland to many European cities. My county is next to Somerset. It was here that king Alfred hid from the Vikings in the very watery landscape that existed then. It was in this location that he burnt the cakes. This is quite a good piece about it.

        To this day several of the higher places in the somerset levels have Anglo Saxon names indicating they were islands. Glastonbury tor stuck up above a vast inland sea.

        As an illustration of the rich repository of documentation that we can all on in our research we still have king Alfred’s will!

        Our present queen is descended from him.


      • Scott

        Thought you might enjoy this. I wrote About doggerland of course in part one but did you know there was a Victorian scheme to reclaim the land?

        These days there are some vast wind farms situated on the doggerland. I flew over them a few weeks ago.

        A little further south a remnant of drowned land emerges from the sea at exceptionally low tides and a team plays cricket there! See picture at end of link


      • tonyb
        Thanks for the reminder of Dogger land.

        Do you think Jim D could comment on sea level rise on 3 mm year acceleration after reading and looking at that?

        I enjoy rational discussion here but not wild claims of disaster.

        Ireland used to be linked to GB. There ;used to be an ocean connection between the Atlantic and Pacific oceans. Closing that changed ocean circulation and may result in ice ages.

        The Earth Abides. Big changes all the time.

        Good luck on the sea level II paper.

      • Scott

        I think you made a crucial comment in your penultimate sentence. There have been constant changes in climate and conditions throughout our history.

        Jimd seems to believe that our previous climate was preserved in aspic and therefore any changes that happen now are unique and to be feared.


      • In order to be a meltwater pulse it will be necessary for there to be an energy pulse.
        NO! not even close!
        Energy is almost unchanging, melting is changing slowly, a Meltwater pulse occurs when the collapse of a huge moraine dam occurs.

      • Have to give you credit Jim D, you have a well honed knack for making things up.

        As in “… Current sea levels are below the value they should be for current temperature by several meters.”. And you know this how?

        And further down you talk about more severe winters. From global warming. Right.

      • timg56, sea levels are higher when it is warmer. This is not rocket science.

      • Geoff Sherrington

        “loss of river flux”
        People tend to take incoming water, use acting amount, then let it pass on.
        Not a great deal of the flux taken?
        OTOH, if man dramatically increases evaporation, the effect is larger. Still not convinced this is a major effect on sea level esp when man is also helping artesian waters to top up the sea. Need numbers to put the effort of man into perspective?
        Still amused that the bottom half of the ocean is so data poor yet plausible basin geometry changes are not included in SLR models.

      • Geoff,

        “People tend to take incoming water, use acting amount, then let it pass on.
        Not a great deal of the flux taken?”

        You must be from a country where it rains quite a lot. Agricultural use of water can dry entire rivers. In many countries it is highly regulated, and some of the laws are centuries old.

        This is the Tribunal of the Waters of Valencia in session at the cathedral portal. This tribunal was already working under Muslim authority during the Caliphate period in Spain around 960 AD. It is a UNESCO Intangible Cultural Heritage.

    • “temperatures are rising a few more degrees yet in this century”


    • Jim D,

      You seem to ignore that meltwater pulses originate from proglacial lakes that accumulate water from melting against a wall of ice that eventually fails. Do you see any proglacial lake that fits the bill currently where meltwater is accumulating?

      Meltwater pulses have not occurred countless times in the paleo record. There are very few meltwater pulses that the experts agree have had a significant effect on sea levels. Mainly MWP 1B and 1A.

      I dissent that we have sufficient information that “sea levels then were likely a few meters higher [at] mid-Holocene.” They were a few meters higher during the Eemian, but not during the Holocene.

      The problem with future scenarios is that one of them sees me as a big lottery winner, however it doesn’t seem to come to pass. The cautionary principle says that I should at least buy the ticket, but being a scientist I’m a bit of a skeptical since the chances are no good. However Hansen seems to score a winner every time he builds a future scenario no matter its chances. He is smart as he collects his winnings beforehand.

      • MWPs also occur from collapsing ice sheets and surging ice streams, but you seem to have dismissed that possibility. Sea levels are lower than they were last time it was this warm, and with several more degrees we reach global temperatures that prehistorically have not supported glaciers. This paleo evidence tying global temperatures to glacier extents is not to be ignored, especially as we get nearer the margins where any glaciers can be stable.

      • By the way, your own sea-level diagram supports that sea levels were higher earlier in the Holocene, possibly by meters, and I have seen that elsewhere too.

      • Yes, we know that Earth glaciers were very much reduced during the HCO, and summer Arctic sea ice was very much reduced or even essentially ice-free. That sea levels were higher is pretty much a given, but by how much? I seriously doubt that it was by several meters except at some basins were isostatic adjustment has played a role. I think that the truth is that nobody knows so I don’t think you can make much of an argument from lack of evidence.

        We come from a recent (350 years) situation when all the records in Holocene glacier extent were broken. It is clear that the relationship between temperatures and glacier extent, adequately corrected by precipitations still holds, and that glacier reduction significantly predates CO2 emissions.

        The occurrence of all sized MWP is not very much discussed. What it is discussed and a lot in the literature is their effect on oceanic currents and climate. The evidence for that is flimsy at best.

      • This is probably the best we can do in terms of Holocene sea levels, from Lambeck et al., 2014

        We lack resolution, but it is hard to defend significant sea level changes after the melting of ice sheets around 7000 years ago. We are probably looking at changes of a fraction of a meter as we face now.

      • The sea level rise rate since 1990 is double the average value in the 20th century. This is not surprising given the warming and consequent increased loss rate of glacier mass recently. This is not a steady loss, but an increasing one, especially from Greenland, which is why I don’t dismiss a new MWP so easily.

      • I have seen those paleo sea level reconstructions, but I have also seen several like this, for example, that is consistent with your Fig. 25.

      • “The sea level rise rate since 1990 is double the average value in the 20th century. This is not surprising given the warming and consequent increased loss rate of glacier mass recently.”

        How should we know? We are measuring it in a different way, so it is not directly comparable. What we do know is that since 1993 the acceleration has been exactly zero, so any previous acceleration with worse data is suspect.

        The lack of acceleration is a sore wound in the CO2 hypothesis because in that time about 40% of all human emissions have been produced.

        The response of scientists is to say that we will soon see the expected acceleration.

        Fasullo, J. T., R. S. Nerem, and B. Hamlington. “Is the detection of accelerated sea level rise imminent?.” Scientific Reports 6 (2016).

        So the evidence does not support an increased rate of temperatures increase, or sea level rise. It is very curious that alarmists will reject this empirical evidence. It seems to postpone the day of reckoning that they so much fear.

        Regarding that reconstruction, does it come with a scientific citation? You seem to be allergic to them. Most sea level reconstructions are local and vary a lot. I looked into the issue with some detail. Very few reputable sea level experts are willing to advance global reconstructions given the level of uncertainty.

      • Javier, compare the rise rate since 1990 with the 20th century average. You will see the acceleration there. Sea-level rise rate is more robust if you look at it in 25-year or 50-year segments. The acceleration is clear when comparing the last 25-year segment with previous ones. Skeptics don’t seem to think to compare these longer more robust averages, and I don’t know why.

      • The skeptics can argue among themselves if Holocene sea levels have been higher. This is a skeptic site that makes that case. To me it doesn’t matter, but it would not be so surprising.

      • Well sorry Jim D,

        But when I look at it longer time I don’t see the acceleration that you claim, only the 60 year cycle that is apparent everywhere, from the Gomez glacier (responding to SAM), to HadCrut or AMO.

        Wyatt & Curry, 2014, explain very convincingly why the cycle appears to shift for its different manifestations.

        Whatever acceleration is to be found in sea level rise is clearly not due to CO2 emissions.

      • “The skeptics can argue among themselves if Holocene sea levels have been higher. This is a skeptic site that makes that case. To me it doesn’t matter.”

        Because you have a different agenda? Holocene sea levels do not advance your cause?

        That is a clear difference between science and activism. You are an activist. Discussing science with you is a waste of time.

      • Jim D ignores that there is cyclical behavior with respect to sea level rise. He’d be one to measure temperature going from winter to summer and conclude that it’s worse than we thought.

      • Javier, you did not calculate the mean rise rate for the 20th century from your graph which is half that of the last 25 years. That is an acceleration, even a doubling, that you may or may not have noticed. I am just bringing this to your attention.

      • Javier, having higher sea levels at the Holocene Optimum is consistent with temperature reconstructions that show a gradual cooling between then and the LIA. Paleoclimate has a lot to tell us about sea level and even slight temperature variations like that.

      • Jim D,

        You are comparing apples and oranges.

        Jevrejeva’s work shows no acceleration between 1860 and 2000. Satellites don’t show any acceleration between 1993 and 2017.

        Sorry, the evidence does not support what you say. No acceleration in sea levels rise.

      • Unbelievable. You are comparing two line segments with the more recent one having twice the gradient of the old one, and saying no acceleration.

      • Are you thick, Jim D?

        I already told you that they are apples and oranges. Jevrejeva et al., 2006 used a database of global tide gauges. You cannot compare the rate that you get with tide gauges to the rate that you get with satellites. Different techniques, different adjustments.

        None of them shows any acceleration. They overlap between 1993 and 2000. If there was any acceleration it should appear in any of them.

        It is amazing how you can ignore evidence to promote your activism.

      • Javier: “Very few reputable sea level experts are willing to advance global reconstructions given the level of uncertainty.”

        Doesn’t stop us amateurs from giving it a go:

        If I were a betting man, I’d make a small wager that 21st century SLR will be in the 1 foot range, give or take a few inches. So a slight acceleration from the previous century.

      • You can even put them together and some people have. Tide gauge is currently running faster than even satellite and that itself was twice what tide gauges did in the 20th century.,_1880-2013.png

      • Jim there you go making the same inaccurate statement about rate of SLR doubling since 1990 from the 20th century average. Get a clue. You only get that by switching from tidal gauge data to satellite data. Since tidal gauge data hasn’t shown an increase in rate, the difference between the two sources are most likely a methodology induced error.

        If you can’t get that one right, how do you expect anyone to take you seriously on anything else?

      • timg56, compare the tide gauge. I posted it just above. Glad to help, but you should be able to find this out for yourself.

      • ‘The global sea level trend from the beginning of satellite measurements in 1993 up to 2014 is 3.2 mm/year. The sea level trend for the period 1993 to 2009 calculated from tide gauge records is 2.8 mm/year very close to the satellite altimeter global sea level trend.’

        Tide gauges are used to adjust for altimeter drift – although this is not apparently calibration. The apparent acceleration is purely an end effect.

      • Again, ignoring the 20th century average for some reason. Surely a century average is a fairly precise rate for comparison here.

      • Jim D.

        Unbelievable. You are comparing two line segments with the more recent one having twice the gradient of the old one, and saying no acceleration.

        Yes, it is a very normal acceleration, wich happens now and then.

      • Geoff Sherrington

        This sub thread on sea level rise would be much clearer if there was mention of a (possibly?) simple number.
        What is the calculated rise of the surface of the oceans relative to the average land position, following a 1 degree C rise in atmospheric temperature?
        In a sense I am viewing the oceans as the alcohol in a LIG thermometer and saying ‘you heat me 1 degree and I will expand this much’.
        I realise that salinity enters the equation, some non-linear relations are present in the 0-4 deg C range near freezing point and so on. But someone must have worked this into a rule of thumb with error bands.
        There could be many unknown knowns also – like, does biological growth in the oceans increase in hotter water, taking building blocks from the air and enclosing rocks and creating a new mass in the oceans, pushing up the sea level. There are so many of these thought bubble effects that I ask if there has been a systematic listing of them in a paper, with estimates of possible magnitudes.
        It is sobering to think that sea levels around the continents might have changed in the distant past when the Hawai’ian Islands rose from the abyssal plains to a substantial height. Sure, it might have been a slow process, but we are talking mm of change a year. How do we know that this process is not operating now andeconfusing the measurements, the alleged accelerations, etc?
        Climate research meets such diffuse objections time and again, often with a decision to ignore and forget. At some stage the summation of all these ignore and forget factors could well be a significant figure, throwing some past hypotheses out the window.

    • Jim D

      And thank you for acknowledging and giving legitimacy to my favorite acronym, MWP.

      It has a nice sound to it.

  23. Javier,
    Thank you for a very interesting and informative article. One query. You say:

    “Two thirds of this meridional heat transport is achieved via the atmosphere and one-third via the oceans in the Meridional Overturning Circulation system (Trenberth & Solomon, 1994).”

    Although that is not a central part of your story, for the record, I’m not sure that’s still thought to be the case. My understanding is that cross-equatorial heat transport is now believed to be about 0.4 PW northwards by the ocean, partially balanced by about 0.2 PW southwards by the atmosphere.

    • Hi Nic,

      Meridional transport is a complex issue where oceanic transport dominates at sub-tropical level and atmospheric transport dominates at mid and high-latitudes. I did not want to enter into the details of it since it is peripheral to the article.

      This figure from a Nature article of 2015 shows the current understanding.

      I believe that you are correct in that cross-equatorial transport is slightly favorable towards the Northern hemisphere thanks to the Atlantic. In my opinion this difference is crucial, as it is the basis of the polar seesaw hypothesis and could have been crucial to the development of the Quaternary Ice Age since the closure of the Panamanian isthmus.

  24. “The closure of the Panamanian Pacific-Atlantic connection converted the North Pacific Ocean into a cul-de-sac for the meridional heat transport.”

    This mantra is a pet peeve of mine as it makes no sense. It is the restriction at the Bearing Strait that isolates the Pacific from the Arctic Oceans.

    The restriction at Panama was roughly equal to the current Bearing restriction in the late Miocene, long before any NH glaciation.

    Furthermore, the “Panama” connection prior to restriction was tropical and “zonal” rather than meridional. Seemingly this connection would have allowed trade wind driven surface currents to extend from Africa to SE Asia.

    The net result of the closure at Panama may well have been to INCREASE the efficiency of meridional energy transport. The closure would almost certainly increased the teleconnection between the poles.

    [End of rant on a topic peripheral to a very fine and much needed effort]

    • Gymnosperm,

      A crucial issue of the Panamanian closure appears to be the changes to salinity. Since its closure evaporation takes water out of the Atlantic basin into the Pacific, leaving its salt behind. The warm saltier waters move northward sinking to the subsurface level, so the Atlantic Thermohaline Circulation is based mainly on the closure of Panama. The result appears to be a colder Arctic than otherwise.

      • It is debatable that the thermohaline circulation is real in the cartoon “conveyor belt” sense. Jim Steele has done some work on this. The thermohaline flow cannot be measured. It can only be supposed.

        In any event, an increase of warm saline water in the gulf stream rather than across the Caribbean to the Pacific strikes me as increasing poleward energy transport.

      • Perhaps you are right Gymnosperm. I am no expert in oceanic circulation and it is a very complex issue, so I do not feel very confident when arguing about it. I do know that the North Atlantic is the saltier ocean, and this is probably due to humidity export to the Pacific that is favored by the closure of Panama. It also appears that there is a relationship between salinity in the Caribbean and temperature stages during the past glacial period that suggest that heat transport and salinity there are somewhat inversely correlated.

        Schmidt, M. W., Spero, H. J., & Lea, D. W. (2004). Links between salinity variation in the Caribbean and North Atlantic thermohaline circulation. Nature, 428(6979), 160-163.

        “We find that Caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2, 4 and 6, and lower salinities during the warm stages 3 and 5, covarying with the strength of North Atlantic Deep Water formation. At the initiation of the Bølling/Allerød warm interval, Caribbean surface salinity decreased abruptly, suggesting that the advection of salty tropical waters into the North Atlantic amplified thermohaline circulation and contributed to high-latitude warming.”

        I find all this quite interesting, and while I believe that the effects of the closure of the Panama isthmus are hotly debated, it can at least be argued that Meridional Heat transport became isolated between both oceans. Prior to the closure it is not very risky to imagine that warm salty waters from the Caribbean were pushed to the Pacific, keeping the salinity in the Atlantic lower than current.

    • It is all highly speculative. Something caused a shift to the Pleistocene ice age – and the shoaling of the Isthmus of Panama seems a plausible hypothesis.

  25. Javier, thank you for the essay. I’ll devote some time to rereading it, the comments, and your responses to the comments.

  26. You and Andy May have provided top notch posts. Both were very enjoyable reading and educational, as well.

  27. Javier,
    Also thanks from SF


  28. “So it is clear that unusually strong tides take place with centennial periodicities capable of exerting powerful vertical mixing even below sea ice, thus providing a mechanism for triggering a Dansgaard-Oeschger abrupt interstadial warming.”

    I have doubt that the ‘tidal vertical mixing’ is the trigger for the D-O abrupt changes.
    North Icelandic Jet (NIJ) current is the key modulating component of the Atlantic Meridional Overturning Circulation (AMOC). The NIJ current’ intensity changes are most likely related to the tectonic activity along the MAR at Kolbeinsey Ridge located north of Iceland.

  29. Vukcevik,

    That a tidal cycle could explain the triggering of D-O events through vertical mixing doesn’t mean that a tidal cycle is responsible for doing so.

    However any other possible cause has to explain how after disappearing three times, at 65, 50, and 20 Kyr BP (figure 25), the 1470 year signal reappears thousands of years later with exactly the same pacing, three times. The chances of internal variability producing that effect by chance are close to zero.

  30. Dr Curry, if you even need a break, please feel free to repost any of my articles over at CO2isLife.

    Climate “Science” on Trial; Cherry Picking Locations to Manufacture Warming

  31. Javier
    Great review – blog science of the first order!

    What is your take on the hypothesis of Wunsch 2000 that a ~1500 year spectral line in Greenland and other palaeo records is an aliasing artefact:

    And here is a refutation of Wunsch 2000 by Meeker et al (Mayewski, Grootes, Alley, Bond):

    • Hi Ptolemy2,

      I share with Wunsch the discomfort that the narrow peak of the Dansgaard-Oeschger band at the 1470 year frequency provokes. This sort of precision has only been seen in Milankovitch cycles in the climate system, where the 41,000 year band or the 19,000 and 23,000 year bands are clearly defined in climate responses like 18O or sapropels over millions of years. We are facing that type of precision.

      However I agree with Meeker, Mayewski, Bond, Alley and Grootes (what a list of who is who), that the problem cannot be an aliasing of the yearly signal. Even when counting ice layers, the seasonal signal dilutes and disappears quite early through diffusion. Wunsch is finding a mathematical solution that is not warranted by the nature of the data. Mathematical analysis in climatology has to be done with great care to the nature of the data, as it is of a very different nature from the data that is produced by laboratory equipment.

      I believe the 1470 year signal is very real and it is supported by very good evidence. It is not only ice cores. Pollen analysis in lake sediments and ice rafted debris in marine sediments support it. Ice cores provide the best dating technique available, even if not totally precise. To me the explanation for the precision of the narrow peak at the 1470 year signal can only come from a Milankovitch type of precision in the cause. In other words we are likely looking at an orbital cause. That’s why I have looked at the tidal origin. I simply cannot think of anything other than an astronomical cause that can produce that type of precision over tens of thousands of years. And there is evidence that Heinrich events, and likely D-O events, have been taking place during previous glacial periods, perhaps for millions of years.

  32. “If the Site 609 HSG variability is indeed solar in origin, a more parsimonious explanation is that it is directly related to the observed variability in the inferred forcings, the 1000 and 2000-year periods that are present in both Holocene atmospheric14C production and ice core10Be flux (Fig. S4). This is consistent with both wavelet analysis (Fig. 6) and age uncertainty modelling (Fig. 7) results that indicate these components are strongly significant throughout glacial Stages 2 and 3. The lack of these oscillations during the extended warm periods of Greenland Interstadial 12 (~43-47 ka) and 13-14 (~50-55 ka) may reflect circulation changes similar to those proposed for the Holocene(Bond et al., 1997). The low late-glacial sedimentation rates at Site 609 (Fig. 3) preclude the detection of 1000-year periodicity from 15 to ~ 30 ka, which is indicated by the regions of Fig. 6 from which shading is removed.Therefore, the “1500-year cycle” is more likely to be either an artifact of arithmetic averaging or the result of chronological uncertainty.”

    • Obrochta et al., 2012 are mistaken. Benthic cores cannot be used to conclude that the 1500 year cycle does not exist, because their dating is a lot more imprecise than ice cores, and the 1500 year cycle was described in ice cores. Site 609 has one of the best registers of Heinrich events, and Heinrich events are a part of the D-O cycle. Heinrich events end in a D-O interstadial warming.

      The idea that the 1500 year cycle can be explained by an averaging of two solar cycles has been pushed by several authors. It simply does not hold water. Solar cycles cannot explain the D-O cycle. No question about that.

    • @ Robert I. Ellison
      1000 yr periodicity is of solar origin (Steinhilber) but most likely is an average of two closely spaced components as found in the stalagmites (providing accurate annual resolution) in the Chine’s Dongge cave.
      (click to enlarge)
      1450 yr periodicity appears to be there, but below what I would consider noise level.
      Korte Geo-Polar is spectral composition of the (Arctic vs Antarctic) earth’s magnetic field, which may or may not be related to the climate, but nevertheless an interesting coincidence.

      • Hi Vuk – yes – thanks. The idea emerging is that solar UV/ozone interactions at the poles change sea level pressure which in turn drive polar storms more or less into lower latitudes. These drives synchronous changes in global resonant and chaotic subsystems – including ice rafting events.

  33. What is the justification for the belief that damages of global warming will exceed the benefits? Consider these points:

    1. Average global temperature for the past 650 Ma (i.e., since complex life began) was 7C warmer than now (Figure 15 . Life thrived during warm times and struggled during cold times. That does not support the belief that 2C or 3C will be harmful.

    2. There is 4 to 10 times more carbon tied up in the biosphere now (3,000 GtC) than at the last glacial maximum (300-700 GtC). This shows life thrives in warmer times.

    3. The planet will not get out of the current cold house condition until the tectonic plates re align (tens of millions of years in future). Again, this does not justify the belief that GHG emissions will cause substantial increases in GMST.

    4. Empirical studies suggest ECS is much lower than the IPCC has been saying for the past 30 years. Again, this does not support the belief that GHG emissions will cause substantial increases in GMST.

    5. Richard Tol (2013) projected that global warming would be net beneficial to beyond 4C of warming (excluding the projected cost of energy consumption) – Figure 3 (bottom chart) . The projected cost of energy consumption may be grossly exaggerated for reasons I explained here:

    6. My replot of William Nordhaus DICE-2103R net benefits of proposed mitigation (carbon price) policies per 5 years to 2100, using the default inputs (except red line), shows net benefits would be negative this century. The red line is the nearest to being possible (but still highly improbable – see text here: )

    Taking these points together, it seems pretty hard to justify the belief that GHG emissions are doing or will do more harm than good.

    • Re point 1 above, Figure 15:

      We are currently in a deep coldhouse phase only the second in the past 650 Ma, and near the beginning of it (compare duration of current cold house phase with the one 300 Ma ago). We won’t get out of it until the tectonic plates realign. That will take tens of millions of years. Were stuck in a coldhouse phase. GHG emissions are beneficial. They are increasing biosphere productivity and reducing the risk of abrupt cooling – and delaying and reducing the magnitude of the decent to the next glacial maximum.

  34. “Now imagine that you have never seen the device and that it is hidden in a box in a dark room. You have no knowledge of the hand that occasionally sets things in motion, and you are trying to figure out the system’s behavior on the basis of some old 78-rpm recordings of the muffled sounds made by the device. Plus, the recordings are badly scratched, so some of what was recorded is lost or garbled beyond recognition. If you can imagine this, you have some appreciation of the difficulties of paleoclimate research and of predicting the results of abrupt changes in the climate system.” NAS (2002) Committee on Abrupt Climate Change

    I started with this quote to suggest that seeing an illusory precision in paleological data was bound to mislead. I am prepared to discuss alternatives but the bare insistence that there are no pseudo 100,000 years pseudo-cycles – or that 1570 year pseudo-cycles are not an averaging artefact of 1000 and 2000 year pseudo-cycles becomes dogmatism – rather than a nuanced judgement in the face of great uncertainty.

    I say pseudo because these are not cycles but shifts in a chaotic system involving a trigger and multiple – indeed global spanning – mechanisms. Many of which we don’t half understand and some of which are completely unknown.

    Javier rejected out of hand two references I supplied – misrepresenting both I believe. Nor did I insist they are right – just different dimensions of the same problem. There is no correct answer – especially with such partial data available – but he insists that both are wrong. More generally the climate blogosphere rejects evidence it disagrees with – and adopts that which it approves of.

    • This is one of the quotes.

      “If the Site 609 HSG variability is indeed solar in origin, a more parsimonious explanation is that it is directly related to the observed variability in the inferred forcings, the 1000 and 2000-year periods that are present in both Holocene atmospheric14C production and ice core10Be flux.”

      And the reply was?

      Reject on the basis of benthic sediments being less accurate – but that is clearly not the point.

      • “Javier rejected out of hand two references I supplied
        There is no correct answer
        More generally the climate blogosphere rejects evidence it disagrees with.”

        I completely disagree with you. You might ignore it, but the nature of science is such that the same evidence can be and is interpreted in different ways by different scientists. However there is a correct answer, and only one of the interpretations is correct and the rest are wrong, only often we don’t know yet which one. Or do you think that both Lamarckism and Darwinism are correct? or that both are equally incorrect? Darwinism might be incomplete as formulated, but it was a correct interpretation of the evidence. Lamarck was wrong. End of the story.

        There is a ~ 1470 year climate cycle during last glacial period or there is not. And one of these answers is the correct one. There is a ~ 100 Kyr climate cycle during Late Pleistocene or there is not. And one of these answers is the correct one.

        I gave you my take on those two works.

        Obrochta et al., 2012 reject consensus and redate a single benthic core, the one that better supports the ~ 1500 year cycle, and on that basis alone reject the ~ 1500 year cycle. However they ignore the strongest evidence that supports the ~ 1500 year cycle: Every Arctic ice-core shows it very clearly not only in 18O but in multiple isotopes. And every Antarctic ice core shows it in methane. Obrochta et al., 2012 are clearly wrong in their conclusions. Their redating of site 609 might be correct and their work merit publication even if their hypothesis is wrong. The rest of scientists have not thrown away their results that contradict Obrochta et al., 2012 and run to embrace their conclusions.

        With the 100 Kyr cycle we have the opposite situation. The consensus is that it determines the interglacial periodicity and only a few specialist scientists reject this consensus. I base my position on my own analysis of the data and on a extensive consideration of the data published by both sides. The 100 Kyr cycle introduces lots of problems. The 100 Kyr problem and its related 400 Kyr problem are significant enough to merit their own Wikipedia page.,000-year_problem

        If you bring papers to the comments of my article, I suppose it is fair that I can give my take on them. Lee et al., 2017 is a work that tries to give an answer to the 100 Kyr problem. It is like those works trying to explain the pause in global warming. Science with a predetermined solution. This type of science can be right or wrong, but it starts already biased. In my opinion the article is wrong because the 100 kyr periodicity of interglacials is an artifact of the data that has been carried over to become consensus. Occam’s razor supports that obliquity was responsible for interglacial spacing in the Early Pleistocene and is still responsible for interglacial spacing in the Late Pleistocene.

        The climate blogosphere is full of people with little understanding for science and little scientific background, which is just obvious because they are no scientists. No fault of their own. As the causes of climate change are a political debate, most people first take a position and then practice evidence selection to support it. Such is human nature. But you are no better. Your statement that “There is no correct answer” is very far from science, as scientists are always looking for the correct answer. And I have noticed that in any article of Judith Curry’s blog you practice shameless promotion of your blog and your ideas with total disrespect for the issue being discussed, the author of the article, and Curry’s blog, that you are using for your own benefit. A lot of people here are already realizing what you are doing. And no. I did not reject your references out of hand. I always give careful consideration to what i say. I had Obrochta et al, 2012 in my hard drive, and downloaded its data (and Obrochta et al., 2014) on December last year to analyze both detrital carbonate and hematite stained grain data. It is not out of hand.

      • There were three ideas introduced. Holocene variation in the Pacific that has some similarity with Bond events – the Holocene manifestation of D-O events. There was the question of the 1500 year periodicity being a statistical artefact. And the new idea – published last month – of Antarctic sea ice being implicated in glacial initiation. All interesting to anyone who doesn’t have a fixed view.

        On the first you repeated what I said. On the second there was some idea that the quasi 1000,000 year glacial/interglacial cycle was a myth. The interesting bit was the Antarctic sea ice. And then you rejected Obrochta et al, 2012 on the grounds of benthis sediment records when the reference was to Holocenr records of carbon isotope production and beryllium isotopes in an ice core. All completely on topic as I understand it and with absolutely no link to blog or related FB page. I don’t recall writing on the topic – although I have done sporadic reading over the years.

        Obliquity btw is a partial explanation for quasi 1000,000 year spacings of interglacials – which is quite obviously not a myth.

        There are 1000 year shifts in Pacific state. More salt in a Law Dome ice core is a cool Pacific state and rain in north-east Australia.

        There are 2000 year spikes in the Moys and colleagues graph I provided earlier – as well as the mid-Holocene transition from a cool to warm Pacific that dried the Sahel. Moreover, periodicities change – e.g. “Spectral analysis shows the below-average epochs are associated with enhanced ENSO-like variability around 2–5 yr, while the above-average epoch is associated more with variability around 6–7 yr.”

        There are many different ideas based on very limited and uncertain data. There has of course since Bond been considerable discussion about many different periodicities. I doubt that the last word has been spoken on this. There are different paradigms – but sometimes definitive answers are elusive. Especially if the wrong questions are being asked. I am inclined to think there are no fixed periodicities – instead climate shifts in its multi-dimensional state space when triggered by an environmental factor.

        I am an engineer, hydrologist and environmental scientist. My strength is a broad background in science, technology and policy. The answers to climate etc are far broader than science.

        And my blog and related FB page is a personal resource on science, technology and policy. Sharing is of course the point – but I am afraid if I were interested in self-aggrandisement I’m in the wrong field.

        I write about development and the interface with the natural world. My interests include water treatment technology – everything from the CRAPPER low-cost toilet to ion exchange equipment for recycling acid mine drainage. More broadly in managing the urban water cycle – water supply, stormwater and sewage minimise impacts on the environment.

        My hydrological background involves an ongoing interest in global ocean and atmospheric circulation and in hydrodynamical modelling. Environmental science expands that to biogeochemical cycling – the movement of substances through global environments – and to energy technology, economic development, climate policy, environmental risk assessment and environmental law and management.

        I have enough physics for anything in climate science, I have studied the Pacific system – as drought and flood dominated regimes – since before the decadal to millennial aspects were a thing. I have been running hydrodynamical models for decades. And I am an environmental scientist – trained to cross disciplines and to facilitate multi-disciplinary approaches to wicked problems. And climate blogs are anathema – I wonder why.

        I have a climate hypothesis – that the Pacific will be yet cooler after the next climate shift. Due in a 2018-2028 window. The environmental trigger is solar UV.

        But that climate science is almost irrelevant to policy.

      • quasi hundred thousand not million of course…

      • “Bond events – the Holocene manifestation of D-O events.”

        If you believe Bond events are the manifestation of D-O events during the Holocene you have not studied sufficiently neither Bond nor D-O events. A simple question, what is the periodicity of Bond events? Is it the same than D-O events?

        “And then you rejected Obrochta et al, 2012 on the grounds of benthis sediment records when the reference was to Holocenr records of carbon isotope production and beryllium isotopes in an ice core.”

        You have not even looked at the figures of Obrochta et al., 2012, yet you bring it to the discussion. Obrochta et al., 2012 refers to DSDP site 609 which is a core from the last glacial period, and has nothing to do with the Holocene. In fact, the most recent date for 609 is 14.41 Kyr BP, before the Holocene even started.

    • “There is some evidence that this cycle may also be present in the Holocene
      but does not trigger DO events then [Bond et al., 1997], possibly because the Atlantic ocean circulation is not close to a threshold in a warm climate [Ganopolski and Rahmstorf, (2001]. The so-called ‘‘little ice age’’ of the 16th –18th century may be the most recent cold phase of this cycle.”

      You don’t seem to have read or understood your own reference. And completely misrepresent the Obrochta et al., 2012 quote – and against all odds persist in it.

      To repeat the quote.

      “If the Site 609 HSG variability is indeed solar in origin, a more parsimonious explanation is that it is directly related to the observed variability in the inferred forcings, the 1000 and 2000-year periods that are present in both Holocene atmospheric14C production and ice core10Be flux.”

      And the reply was?

      Reject on the basis of benthic sediments being less accurate – but that is clearly not the point of the quote.

      I am always baffled by this sort of behaviour. You do your credibility no favor by persisting in this. Fortunately I have the option of not continuing with pointless discussions.

      • “If the Site 609 HSG variability is indeed solar in origin…

        I have the option of not continuing with pointless discussions.”

        There is absolutely no evidence that Site 609 HSG variability is indeed solar in origin. That is one of several things that make this discussion pointless. It is all baseless speculation on your part.

      • How do you think that carbon and beryllium isotopes are formed?

        Have you really missed such a big part of the picture? And then you decide that the peer reviewed science is speculation on my part? If I were you I would stop digging Javier.

      • How do you think that carbon and beryllium isotopes are formed?

        The problem, Robert, is that we are talking about an article that you either have not read or have not understood.

        I’ll try to explain a little:

        Core DSDP site 609 goes from 14.41 Kyr BP to 70.84 Kyr BP. Most of the core age is outside 14C determination limits. In fact Table 1 of Obrochta et al. 2012, shows that they only use 14C determination for the first 175 cm of the core to an uncorrected 14C age of 11,500 to 31,120 years. They use this determination in Figure 3 to establish the age model, together with a NGRIP comparison and sedimentation rate.

        This means that Core DSDP site 609 variability in HSG (Hematite stained grains), that displays a ~ 1500 year variability, cannot be compared with 14C variability. How could it be if it is outside the age range? That you don’t know that is very telling that you talk nonsense.

        And 10Be has not been determined in Core DSDP site 609.

        So I will repeat, how do you or the authors plan to demonstrate that site 609 HSG variability is indeed solar in origin?

        The authors clearly don’t know and are entertaining speculation when they say:
        “If the Site 609 HSG variability is indeed solar in origin, a more parsimonious explanation is that it is directly related to the observed variability in the inferred forcings, the ~ 1000- and ~ 2000-year periods that are present in both Holocene atmospheric 14C production and ice core 10Be flux.”

        Do you get that? They are speculating that HSG variability during last glacial period might be of solar origin and thus related to Holocene solar variability. They don’t have evidence that it is of solar origin.

        But now we have a problem, do you see? Because you either:

        a) Have not read the article and are challenging me after reading an abstract and pretending to be right when you don’t know anything about what you are talking about.

        b) Read the article but did not understand it. Then you don’t have the required level to discuss Obrochta et al., 2012, with me. Certainly you seem to not know that most of core site 609 falls well outside 14C range, indicating that is probably the case regardless of you reading the article or not.

        In any case it is well established that there is no evidence linking Site 609 HSG variability to a solar origin. Obrochta et al., 2012, have not demonstrated such a thing. And it is pointless to discuss with you.

      • “Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured
        in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic’s “1500-year” cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.”

        You have misunderstood the thinking involved. It relies of common dating of both the rafting episodes and cosmogenic isotopes in other records – and during the freaking Holocene in which D-O events are not triggered. And there is far from a single study making this connection.

        The point was the statistical artefact of the 1500 year non-cycle. And the solar origin was something extrinsic to my point but which you seem to have a vehement objection to. And which you denied so soundly with obviously no clue at all about the rationale.

        The problem is that you waffle all over the place constructing some vague and convoluted narrative about how I am missing the point and flavouring it all with disparagement because I have quite reasonably pointed out your shortcomings. You keep digging – and to what point? This is just such childish, petty and misguided nonsense – but it certainly not unheard of the climate blogosphere to go to great lengths apparently just to save face. I will tell you a secret – no one cares.

      • Robert,

        The point was the statistical artefact of the 1500 year non-cycle.

        You keep repeating this in an article about the 1500 year cycle during the last glacial period without showing any evidence for it and you think it is a petty issue?

        “A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic’s “1500-year” cycle.”

        This article doesn’t include the Holocene and states very clearly that D-O oscillations do not and cannot take place during the Holocene because the conditions are not met. If there are no D-O oscillations during the Holocene then it is irrelevant to them that what is taking place during the Holocene is solar forced or not.

        You come here making vague claims about a “Grand Climate System” and saying that the 1500 year is a non-cycle, and when asked for the evidence you talk and talk and have lots of opinions about me. You are all talk and no substance.

      • I f you keep spinning like this you will get dizzy.

        The article called it a statistical artefact.

        I called it something entirely different in response to your silly claim that –

        “The idea that the climate is a random chaotic system is unsupported by massive evidence that climate is determined and limit-bound by a series of cycles and oscillations that in many cases are externally generated. While a chaotic system is unpredictable, a cyclical one is, at least to a certain extent, even if the mechanisms that drive the cycles are poorly known. Humankind has been predicting seasons forever, without understanding what caused them.”

        “In this approach, a complex system is presented as a set of connected nodes. The collective behavior of all the nodes and links (the topology of the network) describes the dynamics of the system and offers new ways to investigate its properties. The indices represent the Pacific Decadal Oscillation (PDO), the North Atlantic Oscillation (NAO), the El Niño/Southern Oscillation (ENSO), and the North Pacific Oscillation (NPO) [Barnston and Livezey, 1987; Hurrell, 1995; Mantua et al., 1997; Trenberth and Hurrell, 1994]. These indices represent regional but dominant modes of climate variability, with time scales ranging from months to decades. NAO and NPO are the leading modes of surface pressure variability in northern Atlantic and Pacific Oceans, respectively, the PDO is the leading mode of SST variability in the northern Pacific and ENSO is a major signal in the tropics. Together these four modes capture the essence of climate variability in the northern hemisphere. Each of these modes involves different mechanisms over different geographical regions. Thus, we treat them as nonlinear sub-systems of the grand climate system exhibiting complex dynamics.”

        Grand climate system has a specific scientific meaning – and I’m sure you can work it out someday.

      • > when asked for the evidence

        Yet O12 is or provides some.

        Please don’t mind Chief if jousting with him gets your eyes away from the ball, Javier.

        You wouldn’t use him to get away with hammering the table with proofs by assertion, wouldn’t you?

      • > “In this approach, a complex system is presented as a set of connected nodes.

        Have you looked at figure 2 of T07, Chief?

        Three nodes. Six patterns. Two sets of three paired by symmetry.

        An intriguing extension of the notion of mechanism.

        That goes right into the Contrarian Matrix. Thanks!

      • The data is available.

        If you want to do some statistical analysis wee willie – feel free.

        And I am sure your ‘qanalysis’ of Tsonis et al (2007) must be correct. I am sure they will be devastated. As I am.

      • > If you want to do some statistical analysis […]

        Epicycles never succeeded in establishing mechanism, Chief, and when self-citing authors weasel their way out with “consistent with the theory of synchronized chaos,” whereby the authors handwave to a short note and a tutorial, you should reach for your wallet.

        A pity you forgot to mention that T07 finds “the evidence for such type of behavior [for the so-called mechanism] in two climate simulations using a state-of-the-art model.”

        Have you explored the citations? Here’s a recent one:

        Some studies emphasize the role of time-varying external forcings36,37,38,39,40 while others stress the role of unforced noise9,28,30,41,42,43,44,45,46,47,48. For these reasons, the ESRUN combines high frequency variability based on the instrumental record with low frequency variability based on reconstructions of surface temperature from the year 1000 to 1850.

        “Emphasis” and “stress” seem to have replaced “mechanism.”

        Also note that the citations in B15 reveals that it’s Tsonis and Kratsov all the way down.

        Please, do continue.

      • It is quite clear that wee willie exhibits little in the way of good faith or a pleasant demeanour.. Where to start is the real question wee willie.

        Brown makes the startling revelation that not all 20th century warming was greenhouse gases – and that warming has slowed since.

        And it would be surprising if high order climate models were not chaotic.

      • From the original post:

        To reiterate, our results indicate that the cumulative warming since the beginning of the 20th century was not possible without positive radiative forcing.

        Brown also says that his study does not exclude RCP8.5 and that it has nothing to do with climate sensitivity.

        Fancy that.

      • I have this red dot on the top of my wordpress site. It’s like my laptop is programming me.

        But to more serious issues – wee wlllie… oh nevermind….

        Actually, wee willies has a reference – he is so proud of it – it says that there was greenhouse gas forcing last century – imagine that?

        The rest was natural variability in chaotic 20 to 30 year regimes.

        But 8.5 is definitely out. It’s a global movement thingy.

  35. Javier, very interesting article. It pushed me to change my idea for a post
    about comparison of spectral behaviours in Holocene and Ice Age to some kind of analysis of DO oscillations. Of course in my spectra of both GRIP d18O and GISP2 Be10 data I can find a quite strong maximum at 1476 year (1448 for Be10) and can reproduce your fig.18
    (red line is a 11-points low pass filter. I note some difference: see e.g. around 45 Kyr BP where you show a maximum [DO12] and I have the minimum preceding DO12 but the plot is the same in its general shape).
    My main concern is that I cannot find your reference to
    Rahmstorf, S. 2003. Timing of abrupt climate change: A precise clock. Geophys. Res. Lett. 30, 1510-1514.
    GRL search engine gives me no results and I obtain the same with a
    manual examination of vol.30.
    May your reference be wrong? If so, can you provide the correct one?
    Thanks in advance. Franco

  36. <a href="http://www.example” rel=”nofollow”>Rahmstorf 2003e

    • francozavatti – Sorry, my html is screwing up, don’t know why.
      Use the title Timing of abrupt climate change: A precise clock. Google Scholar to get a pdf.

  37. Pat Cassen, thank you for the advice. I’ve found the paper. Regards. Franco

  38. There’s so much here for those who have ears to hear!

    The explosive growth of methane during D-O oscillations raised fears that abrupt climate change has repeatedly triggered the hypothetical clathrate gun and that it could happen again in the near future. However deuterium isotopic analysis of ice core methane has shown that the increase in methane was accompanied by a depletion in deuterium (Bock et al., 2010; figure 23). This depletion indicates that its origin is deuterium poor methane from boreal wetlands; one of the main natural sources of methane, and not from deuterium rich clathrate hydrates. The increase in temperatures and precipitation associated with the D-O cycle (figure 19b and c) is then responsible for boreal wetlands expansion and CH4 emissions.

    This scenario is on the face of it the dream scenario for dystopian catastrophists: sharp warming reinforced by emission of a greenhouse gas (methane). But let’s do some science – what is predicted, and what happens. Current AGW paradigm would predict runaway warming with ecosystem devastation as the end point.

    But what actually happens? Not just once but again and again, dozens of times? Does methane reinforced warming continue endlessly until catastrophe? No. Does the warming stop leaving the climate at a new warmer plateau? Again no. What happens is that the warming peak turns out to be just that, a self limiting excursion which promptly reverses itself. Cooling immediately follows so that within a few centuries cooling reverses all the warming and climate is back to square one. No runaway greenhouse warming. Just a cycle of ocean driven (AMOC) warming that self terminates, according to normal behaviour of nonlinear oscillatory systems, and in which “greenhouse gas” warming plays absolutely no role whatsoever.

    • Thank you Ptolemy2,

      The study of abrupt climate changes of the past is very interesting on its own, but there are a lot of lessons to be extracted that apply to the current situation. It is impossible to place global warming in perspective without careful analysis of past climate changes. That is the premise of this series of articles.

      Abrupt changes of the past are often used as catastrophic outcomes of a climate suffering a tipping point and thus examples of the risk presently incurred. However their careful study tends to support an opposite interpretation. They tend to occur in response to very specific conditions, sometimes as a side effect of continental distribution, and never in response to greenhouse gases changes. I believe that by researching and writing these articles, and by reading them, we get a better idea of how the climate works.

      The idea that the climate is a random chaotic system is unsupported by massive evidence that climate is determined and limit-bound by a series of cycles and oscillations that in many cases are externally generated. While a chaotic system is unpredictable, a cyclical one is, at least to a certain extent, even if the mechanisms that drive the cycles are poorly known. Humankind has been predicting seasons forever, without understanding what caused them.

  39. Excellent work by Javier who said:
    “climate is determined and limit-bound by a series of cycles and oscillations ”
    and ptolemy2 refers to:
    “a self limiting excursion which promptly reverses itself. ”
    and ion the past we see vast volcanic outbreaks and meteorite strikes that always fail to induce any significant permanent changes
    Interesting that whatever causes climate variability there is never any imbalance that destabilises the long term hydrostatic equilibrium of atmospheric mass suspended off the surface by the upward pressure gradient balanced against the downward force of gravity.
    Which suggests that the so called greenhouse effect is a product not of GHGs but rather of conduction and convection within the mass of an atmosphere.

  40. “Recent scientific evidence shows that major and widespread climate changes have occurred with startling speed. For example, roughly half the north Atlantic warming since the last ice age was achieved in only a decade, and it was accompanied by significant climatic changes across most of the globe. Similar events, including local warmings as large as 16°C, occurred repeatedly during the slide into and climb out of the last ice age. Human civilizations arose after those extreme, global ice-age climate jumps. Severe droughts and other regional climate events during the current warm period have shown similar tendencies of abrupt onset and great persistence, often with adverse effects on societies.

    Abrupt climate changes were especially common when the climate system was being forced to change most rapidly. Thus, greenhouse warming and other human alterations of the earth system may increase the possibility of large, abrupt, and unwelcome regional or global climatic events. The abrupt changes of the past are not fully explained yet, and climate models typically underestimate the size, speed, and extent of those changes. Hence, future abrupt changes cannot be predicted with confidence, and climate surprises are to be expected…

    Technically, an abrupt climate change occurs when the climate system is forced to cross some threshold, triggering a transition to a new state at a rate determined by the climate system itself and faster than the cause. Chaotic processes in the climate system may allow the cause of such an abrupt climate change to be undetectably small.”

    The climate system is completely chaotic at all scales – the Sun, the Earth, the ocean and atmosphere. From the tiniest turbulent eddy to global events of massive significance to communities and ecologies. Moreover – everything is synchronised in a resonant Grand Climate System in which the whole exceeds the sum of the parts.

    “Finally, Lorenz’s theory of the atmosphere (and ocean) as a chaotic system raises fundamental, but unanswered questions about how much the uncertainties in climate-change projections can be reduced. In 1969, Lorenz [30] wrote: ‘Perhaps we can visualize the day when all of the relevant physical principles will be perfectly known. It may then still not be possible to express these principles as mathematical equations which can be solved by digital computers. We may believe, for example, that the motion of the unsaturated portion of the atmosphere is governed by the Navier–Stokes equations, but to use these equations properly we should have to describe each turbulent eddy—a task far beyond the capacity of the largest computer. We must therefore express the pertinent statistical properties of turbulent eddies as functions of the larger-scale motions. We do not yet know how to do this, nor have we proven that the desired functions exist’. Thirty years later, this problem remains unsolved, and may possibly be unsolvable.”

    Tsonis and Co. confirm synchronous chaos with a brilliant application of network math in the modern era.

    Chaos does not imply random. It implies that tremendous energies cascade through powerful subsystems. It is all completely deterministic but so complex and dynamic as to defy understanding. Humility in the face of immense uncertainty is far more becoming for a scientist than confidence in assumptions that are far too limited in scope. We cannot predict a cold winter to come in Europe.

    These so-called cycles and oscillations are in reality shifts in the multi-dimensional state space of the Grand Climate System that are driven by small changes in environmental factors. Comfortable assumptions notwithstanding.

    • “roughly half the north Atlantic warming since the last ice age was achieved in only a decade”

      I seriously doubt there is evidence for that.

      “The climate system is completely chaotic at all scales”

      Milankovitch disagrees. And so do I.

      “These so-called cycles and oscillations are in reality shifts in the multi-dimensional state space of the Grand Climate System that are driven by small changes in environmental factors.”

      It is a proposal, but likely to be wrong. Changing the axial tilt of an entire planet is not a small change.

      • You may of course need to read the NAS report by a group of very eminent scientists.

        The multi-body problem of the solar systems is of course chaotic.

        As is fluid dynamics of the Sun and Earth.

        The axail tilt produces minor changes in insolation that at the furthest distance from the Sun trigger runaway feedbacks in the Earth system. It is a quasi 100,000 year change in an environmental factor.

        These so-called cycles and oscillations are in reality shifts within the multi-dimensional state space of the Grand Climate System that are driven by small changes in environmental factors. Comfortable assumptions notwithstanding.

        We can’t completely define the state spaced but it is presumed that the system is ergodic.

        You are however completely wrong.

      • I see you have it all figured out. Good for you.

  41. Sorry miss hit. While I’m here, appreciate the post,javier.

  42. Javier, spent a full day backchecking, as DO events were not something I had any deep familiarity with. My congratulations on a very solid and deeply educational post. Bookmarked for all future DO reference. Very nice job. thanks.

  43. Pingback: Weekly Climate and Energy News Roundup #259 | Watts Up With That?

  44. Javier, thank you for you posts digesting this complicated subject for us. The “non-skeptics” believe the observed Cenozoic cooling through the last 50+ ma was caused by the gradual lowering of atmospheric CO2 through increasing ocean uptake due to increasing alkalinity. The hypothesis is that continental plate uplift and erosion of alkaline limestone into the oceans is the underlying cause of CO2 uptake along with the positive feedback of increased CO2 solubility from the cooling. They claim meridonal heat transport efficacy being hindered by plate tectonics (the closing of the Bering Strait and Isthmus of Panama) has nothing to do with cooling. What is your opinion and evidence?

  45. Hi Ron,

    The cooling since the Eocene is the fourth such cooling in the Phanerozoic, even if two of them appear more pronounced. The CO2 explanation is not particularly good to explain what temperatures have been doing for the past 550 million years, and probably we are looking to complex causal events.

    It appears quite likely that continental disposition, if not directly a main cause for Ice Ages, it appears to be an important factor capable of determine how strong Ice Ages are. From the study of past Ice Ages, it is clear that times of super continent break up favor stronger Ice Ages. See:
    Eyles, N. (2008). Glacio-epochs and the supercontinent cycle after∼ 3.0 Ga: tectonic boundary conditions for glaciation. Palaeogeography, Palaeoclimatology, Palaeoecology, 258(1), 89-129.

    The present disposition of continents therefore could have a lot to do with the Quaternary Ice Age being so cold, and the coincidence of the Panamanian isthmus formation provides a mechanism for the last 3 million years cooling. It is however a controversial mechanism. Peter Molnar, who opposes such role reviews that circulation models are capable of showing the entire range of responses to the closure of the Panama Gateway that researchers hold, from precipitating the Ice Age to delaying it.

    Molnar, P. (2008). Closing of the Central American Seaway and the Ice Age: A critical review. Paleoceanography, 23(2).

    I am inclined to think that the position of Antarctica isolated by Circumpolar current, the closure or narrowing of Panama, Indonesia, and Bering straits, with the consequent compartmentalization of the Earth’s oceans have all played an important role in the Quaternary Ice Age being so cold.

    However I think that we are missing another important cause that determines hat cooling periods take place about every 150 million years. Is it the passage of the galactic spiral arms by the Solar System as proposed? Maybe.

    I disagree with Svensmark’s hypothesis that cosmic rays explain climate changes on the millennial timeframe, because the evidence does not support that to be the case. I am not so sure on the multi million year timeframe. The correlation between temperature changes and the passage of the galactic spiral arms that the figure above shows is quite suggestive. We lack a mechanism and the available evidence is not sufficient, but we have to consider that nobody has been able to explain why Ice Ages have been taking place every several hundred million years. I do not think atmospheric changes can explain that.

  46. Thanks Javier. Here is a Youtube Prof. Richard Alley in Dec 2009 at AGU makes the case that all the paleo evidence can only be explained by high ECS CO2 control knob. Although he does begin his presentation by citing skeptics berating him for being deceitful, he proceeds to spend the bulk of his time comparing correlations of temperature to CO2, without mentioning correlation is not causation. When he does finally show the CO2 lag in the 400ka ice cores near the end, (by then the listener has forgotten about the critics,) he claims that CO2 must be the major factor since orbital influences are so weak. He forgets to mention ice albedo. Alley spends considerable time about CO2 and ocean chemistry but neglects to mention that warm oceans expel CO2 and cold oceans absorb, although he brings up that exact dynamic for oxygen in explaining the Permian Extinction, (and why warm kills). I will be mad if Alley has won scientific communication awards for humility.

    I give weight to a lot of what is put forth, including Jim Steele’s Arctic Iris Effect linked by him above, and all the other comments and than the proprietor of CE for allowing them. I do think CO2 has acted as a positive feedback to temp except in extremely volcanic-ally active times and now. The debate is far from over though.
    Cheers, Ron

    • In the past very good scientists have defended completely wrong theories and history hasn’t been kind to them. Humanity has been conducting a daring experiment by putting so much greenhouse gases in the atmosphere and many scientists believe that the climate changes experienced are due to that. They are now reinterpreting all past climate changes to fit their view.

      Given enough time science auto corrects its mistakes. The same experiment we are conducting with the atmosphere is demonstrating that greenhouse gases do not cause as much warming as feared. The warming for the first half of the 20th century is not very different from the warming for the second half, and the beginning of he 21st century is showing very little warming. Not exactly what we were expecting, but we have been lucky that is the case.

      Richard Alley reminds me of Georges Cuvier who made great contributions to science and was one of the foremost scientists of his time. He was however a very harsh critic of those who didn’t share his scientific views and used his high position to attack and discredit them. He is mostly remembered for his stern opposition to any idea of evolution. At his time he was so influential the he essentially created a gap in evolutionism between the first evolutionists, like Lamarck and Geoffroy, and Darwin that published his Origin of species two decades after Cuvier’s death.

      Max Planck famously said that science advances one funeral at a time.

      • > The same experiment we are conducting with the atmosphere is demonstrating that greenhouse gases do not cause as much warming as feared.

        One does not simply appeal to scientific underdetermination, as you so often do, and then pretend experiments demonstrate, Javier.

        There’s no need to wait for the historians to sort out that kind of double standard.

      • Of course experiments demonstrate certain things. That’s the basis of scientific research, reproducibility of experimental results. And of course uncertainty is a serious obstacle to attribution. There is no contradiction.

        A quarter of CO2 in the atmosphere has been put there mainly by human emissions since 1950. That’s obviously an experiment. The result is very little difference in warming rates, glacier melting rates, and sea level rise rates, pre-1950 to post-1950. This increase in CO2 is equivalent in terms of logarithmic effect to the increase in CO2 that took place during deglaciation into Holocene, when a major effect took place in warming rates, ice sheet melting rates, and sea level rise rates. Evidence is accumulating that CO2 does not have the feared strong warming effect.

      • > Of course experiments demonstrate certain things.

        Experiments provide evidence, and here’s what you said yourself about the “nature of science”:

        You might ignore it, but the nature of science is such that the same evidence can be and is interpreted in different ways by different scientists.

        You can’t have it both ways, Javier. Evidence can’t be demonstrative when it pleases you and interpretative when it does not.

        Click on the link under “underdetermination” above, then come back to lecture Denizens about the “nature of science.”

      • Willard,

        You are not a scientist and it shows. Do not try to lecture one about what experiments do or don’t.

        Cleverly designed experiments can help distinguish between opposing hypotheses that up to then were capable of providing alternative explanations to previous evidence.

        One very well known example:

        Triple-stranded DNA was a common hypothesis in the 1950s when scientists were struggling to discover DNA’s true structural form. Watson and Crick (who later won the Nobel Prize for their double-helix model) originally considered a triple-helix model, as did Pauling and Corey, who published a proposal for their triple-helix model in 1953, as well as fellow scientist Fraser. However, Watson and Crick soon identified several problems with these models.

        The double-helix model of DNA structure was first published in the journal Nature by James Watson and Francis Crick in 1953, based upon the crucial X-ray diffraction image of DNA labeled as “Photo 51”, from Rosalind Franklin in 1952.

        As you can see the same evidence was being interpreted in two different ways. The experiment of Rosalind Franklin helped demonstrate that the correct one was the double helix.

        It is you who shouldn’t be talking about the nature of science as if you knew what you talk about.

      • > The experiment of Rosalind Franklin helped demonstrate that the correct one was the double helix.

        That you add “help” to “demonstrate” is intriguing, Javier: aren’t experiments supposed to be demonstrative simpliciter? Also interesting that you’re not using an example from climate science. Since you still fail to read the link I offered you, here’s a tidbit coming from physics, the science all the others are supposed to emulate:

        [I]n fact, what the experiment declares stained with error is the whole group of propositions accepted by Newton, and after him by Laplace and Biot, that is, the whole theory from which we deduce the relation between the index of refraction and the velocity of light in various media. But in condemning this system as a whole by declaring it stained with error, the experiment does not tell us where the error lies. Is it in the fundamental hypothesis that light consists in projectiles thrown out with great speed by luminous bodies? Is it in some other assumption concerning the actions experienced by light corpuscles due to the media in which they move? We know nothing about that. It would be rash to believe, as Arago seems to have thought, that Foucault’s experiment condemns once and for all the very hypothesis of emission, i.e., the assimilation of a ray of light to a swarm of projectiles. If physicists had attached some value to this task, they would undoubtedly have succeeded in founding on this assumption a system of optics that would agree with Foucault’s experiment.

        In the end, holism wins and the myth of the experimentum crucis, the very thing that you’re own interpretative stance rejects, has been refuted.

        I could pay due diligence to your “evidence is accumulating” crap (hint: induction aren’t demonstrative), but life is short.


        > You are not a scientist and it shows.

        I’m just a ninja, dear Javier. and as far as I’m concerned, you’re just a pseudonym on a screen. You could be dog for all I care. If you want to claim authority, post your citations record.

        And no, what you’re talking about is not even science.

      • You can keep talking about science as if you knew what you are talking about. Internet is indeed full of people talking about things they have never experienced.

      • Javier, Pay no attention to Willard. You are correct that he is not a scientist. He is an egotistical word warrior who will twist a phrase, not in order to improve the scientific understanding, but to paint his own logic as superior.

        He does not even understand conventional scientific citations. I had him spam one of my guest essays, accusing me of misrepresenting a scientific paper. I had accurately summarized Mackey’s work and cited him at the end of the sentence as convention suggests. The following sentence prefaced the scientific evidence discussed in the next paragraphs with no refernce to Mackey. But Willard (and Mosher) went on ad nauseum suggesting I had misrepresented Mackey’s work, when in fact Willard simply just didn’t understand how citations work. He even posted an article on Then There’s Physics’ website trying to defend is ignorance and deflect attention from his failure. So again, ignore Willard. He does not pursue scientific truth, only his own odd sense of self aggrandizement.

  47. For millennia scale variability a more subtle mechanism is required. l

    “The past few decades have been characterized by a period of relatively high solar activity. However, the recent prolonged solar minimum and subsequent weak solar cycle 24 have led to suggestions that the grand solar maximum may be at an end1. Using past variations of solar activity measured by cosmogenic isotope abundance changes, analogue forecasts for possible future solar output have been calculated. An 8% chance of a return to Maunder Minimum-like conditions within the next 40 years was estimated in 2010 (ref. 2). The decline in solar activity has continued, to the time of writing, and is faster than any other such decline in the 9,300 years covered by the cosmogenic isotope data1. If this recent rate of decline is added to the analysis, the 8% probability estimate is now raised to between 15 and 20%.

    A number of studies have indicated that the decreases in global mean temperature associated with a future decline in solar activity are likely to be relatively small3,4,5,6,7. However, variability in ultraviolet solar irradiance has been linked to changes in surface pressure that resemble the Arctic and North Atlantic Oscillations (AO/NAO)8,9,10 and studies of both the 11-year solar cycle11,12 and centennial timescales13 suggest the potential for larger regional effects. The mechanism for these changes is via a stratospheric pathway, a so-called ‘top-down’ mechanism, and involves altered heating of the stratosphere by solar ultraviolet irradiance.”

    It sets up changes in sea level pressure at both poles that drive decadal variability – as chaotic shifts – in ocean and atmospheric circulation that persist for decades to millennia.

  48. Javier,

    thank you for the great article.

  49. javier, fantastic article .i enjoy that level of cohesive thinking on such a grand scale even if my lack of education precludes analysis of the supporting evidence.

    one query i have regarding the lunar component . how much of an effect on the d o events does the position of maximum lunar influence acting on the earth have in terms of distribution of ocean water within the various ocean regions/basins . due to the aforementioned lack of education i have difficulty understanding the lunar cycle data that i would imagine is fairly simple for many. so in essence do the peaks in tidal amplitude shown in figure 31 occur in different locations on earth at each peak ?

    how big is the difference in tidal range around these peaks if the maximum lunar effect is centred over the ocean as opposed to land mass, over the pacific as opposed to the atlantic and the northern hemisphere as opposed to the southern along with various combinations of the above ?

    i imagine there is potential for a large variation in distribution of ocean waters depending exactly where on earth the maximum lunar effect takes place.i know this must vary due to precession alone ,but is this variation replicated over geological timescales ?

    i am sorry if this post is not easy to understand. i know what i want to ask, but am having some trouble articulating my point so feel free to ignore this post if it does not make any sense.

    • Thanks bitchilly,

      Tides are quite a complex matter and perhaps I don’t know enough to answer your questions, but I’ll try.

      “how much of an effect on the d o events does the position of maximum lunar influence acting on the earth have in terms of distribution of ocean water within the various ocean regions/basins”

      Although tides originate from the tidal forces exerted by the Moon and the Sun over the entire planet, a multitude of factors affect the time and size of tides at each specific location, so some places have two tides per day and others have only one, and some places have very strong tides and others very weak. It is such a complex matter than until quite recently the best way to make tide tables in most places was simply to register tides for a period of 19 years at the specific place.

      This map from Wikipedia shows how variable are tides at different places.

      The biggest tides have been measured at over 16 meters in Canada, at Ungava Bay, where we can see the effect of tides under sea ice in this interesting BBC video (3 minutes):

      Computer models show that with lower sea levels tides should have been even higher at certain places.

      “do the peaks in tidal amplitude shown in figure 31 occur in different locations on earth at each peak ?”

      No. The increase in Lunar tidal force should affect the entire planet with only the temporal difference of a few days between different locations as the tidal wave travels. There would be tidal peaks separated by 14 and 28 days as it occurs now with spring tides. But the effect would be different at every location as it happens with every tide. Places with higher tides should see a bigger increase.

      Also many times the effect of tides is not direct but through storms that when take place at high water increase their damage factor considerably.

      “i imagine there is potential for a large variation in distribution of ocean waters depending exactly where on earth the maximum lunar effect takes place.i know this must vary due to precession alone ,but is this variation replicated over geological timescales ?

      A big factor that affects tides is obliquity. As the inclination of the Earth axis is bigger, the tractional force responsible for tides increases at high latitudes, increasing the extreme tides there.

      Clive Best has an article on this Milankovitch tides at his blog:

      • thank you for the response javier. that makes things a bit clearer for me.i asked as the last “supermoon” we had the area i spend a lot of time recreational fishing did not experience a particularly big spring tide (east coast of scotland) considering the moon was so close. i was trying to figure out why we had larger tidal ranges earlier in the year when the moon was further away.

        i surmised incorrectly that possibly something like a shift in tidal nodes occurred over long timescales due to slight changes in position of max lunar effect .

        i also saw the low water height remain the same (1.3m on anstruther scale) both in the morning and evening for 4 days consecutively, something i have never seen in the north sea in over 25 years of checking daily tide heights and wondered if this was an unusual phenomena.

        i will read the clive best link later this evening when i have time, it is a subject i have been interested in from the first time i cast a line in the sea. thanks again for taking the time to respond with some interesting information and provide further reading on the subject,it is much appreciated.

      • bitchilly

        This doesn’t specifically answer your question and refers to the recent,rather than distant past, but hopefully you will find it interesting anyway.

        I take a particular interest in tides as I live very close to the ocean in the UK and in our part of the world there is often a huge tidal range which changes considerably as the moon waxes and wanes.

        There are special alerts put out here if there is a risk of sea flooding that coincides with a high tide or a spring (exceptionally high tide)

        I note that several of the American hurricanes were made worse as they coincided with high tides.

        As I have a special interest in highly variable arctic sea ice through the ages I have been curious as to how much the tidal range affects ice formation and break up and whether that has changed over the years. I have a 1906 arctic tide table but it is difficult to find a series in order to compare heights.

        Here is a study from Woods hole about tides and the arctic you might find interesting.


  50. A slow AMOC actually drives a warm AMO and a warm Arctic ocean during an inter-glacial climate. Functioning as a negative feedback to weaker indirect solar.

  51. Are supersolar eruptions classified as d o events ?

    • The quick answer would be no. Either we lack the ability to identify superflares in proxy records or they did not happened. The main case for a superflare within the Holocene is in around 774 AD. If true it doesn’t seem to have had much climatic impact.

      • Javier

        If these superflares were seen in Britain I think they could be identified. Other places would be more random but we have a record for the 8th century as follows (from one of my articles)

        “The rise of Rome coincided with the warm Roman optimum. We are fortunate that we have available the climate references from not only the Western Roman empire, but those of the Byzantine empire (the Eastern Roman empire after the collapse of Rome) approx 380-1453 AD. Collectively, the Egyptian, Roman and Byzantine empires can provide records of some 4000 years of climate change. Geographically this covers a large part of Europe, the Middle East and North Africa.

        Some of the Roman climate references are fascinating. This observation from a series of cold winters -after many warm ones- around the 8th century in Byzantium (centred around Modern day Turkey)

        “Theophanes’ account recalls how, as a child, the author (or his source’s author) went out on the ice with thirty other children and played on it and that some of his pets and other animals died. It was possible to walk all over the Bosporus around Constantinople and even cross to Asia on the ice. One huge iceberg crushed the wharf at the Acropolis, close to the tip of Constantinople’s peninsula, and another extremely large one hit the city wall, shaking it and the houses on the other side, before breaking into three large pieces; it was higher than the city walls. The terrified Constantinopolitans wondered what it could possibly portend.”

        I suspect their influence on climate-as with volcanoes – would be relatively short lived and of course one might be confused with the other.

        Whether the change in climate was precipitated by the event or would have happened anyway is difficult to determine without a large grant for my research :).


      • Hi Tony,

        The mid-8th century cold period that you describe is possibly the 763 volcanic origin cooling, that is well described in:
        McCormick, M., Dutton, P. E., & Mayewski, P. A. (2007). Volcanoes and the climate forcing of Carolingian Europe, AD 750-950. Speculum, 82(4), 865-895.

        You probably already know:
        Ludlow, Francis, et al. “Medieval Irish chronicles reveal persistent volcanic forcing of severe winter cold events, 431–1649 CE.” Environmental Research Letters 8.2 (2013): 024035.

        They have a quite good record of cold periods and analyze which ones coincided with volcanic eruptions recorded in GISP2.

        But as far as I know nobody has been able to link a major solar particle event to climate change in a convincing manner.

      • Javier wrote:
        “The main case for a superflare within the Holocene is in around 774 AD. If true it doesn’t seem to have had much climatic impact.”

        The late 8th century was the warmest period for Europe since Roman times by a number of proxy studies, and yet was the second coldest period in the Holocene GISP2 series. 774-775 AD solar activity would have been especially strong because of a Jovian configuration of the type that occurred in 1934 and 1976, right at sunspot maximum. No doubt the solar wind conditions were generally very strong in the late 8th century, driving a strong positive NAO/AO regime, hence the profound Greenland cooling.

      • Javier linked:
        ‘Volcanoes and the climate forcing of Carolingian Europe, AD 750-950.’

        The very cold winter of 763-64, there is a certain logic why this Jovian configuration produced such a cold event:

  52. Pingback: L’Altalena del Clima nell’Era Glaciale – Eventi, Meccanismi e Conseguenze Storiche : Attività Solare ( Solar Activity )

  53. Javier,

    You said that:

    “No clear 1470-year tidal cycle is known from the data, however one can be deduced [it] from the theory.”

    Yes it can, and it has been deduced in my post at:

    Are the Dansgaard-Oeschger (D-O) Warm Events driven by Lunar Tides?

    This post shows that there is a natural 1470 year tidal cycle for the following reasons:

    When the Perigee of the Lunar Orbit is pointing at the Sun at (or very near to) Perihelion it does not necessarily mean that the phase of the Moon is either New or Full (Syzygy).

    § If we consider the number days that the phase of the Moon is from being New or Full, for each of the FMC’s that are at (or near to) Perihelion. Starting out with a New Moon at Perigee on January 1st (near to Perihelion on January 3rd) in the year 0.00.

    § New or Full Moons that re-occur for FMC’s at (or near to) Perihelion that are whole multiples of 739 years (i.e. 0.0, 739.0, 1478.0 and 2217.0 years) after the starting date, always occur at lunar Perigee.

    § In contrast, New and Full Moons that re-occur for FMCs at (or near to) Perihelion half way between whole multiple of 739 years (i.e. 370, 1109 and 1848 years) always occur at lunar Apogee.

    § Hence, we end up with the following 739.0 year repetition sequence for the times where FMC’s are at Perihelion:

    0.00 Years è New or Full Moon at Perigee
    184.75 Years è First or Last Quarter Moon
    369.50 Years è New or Full Moon at Apogee
    554.25 Years è First or Last Quarter Moon
    739.00 Years è New or Full Moon at Perigee

    § Careful study of the New and Full Moons near 739.0 years shows that the strongest alignment between the phases of the Moon and the 177.0 year Perigee-Perihelion cycle occurs at the FULL MOON at 739.001 years. This contrasts with the NEW MOON at 0.000 years.

    § What this is telling us is that it actually takes 1478.00 years (= 2 x 739.00 years) to complete the cycle with a New Moon at Perigee when a FMC is close to Perihelion once again.

    § The FMC cycle is closest to perihelion at ((1447+1478)/2) years = 1462.5 years, while the lunar phases are most closely aligned with the Perigee-Perihelion cycle at 1478 years – producing a best synchronization at roughly (1478+1462.5)/2 = 1470.3 years.

    §This is in extremely good agreement with the measured spacing of the D-O climate warming events of 1470 years!

    • Hi Ian,

      Yes I find interesting your proposal that a 1470 year lunar cycle can also be found by aligning lunar cycles with the seasons. It is a better explanation of Berger’s proposal that the tidal effect might require a seasonal window.

      Regarding your calculations of when D-O events take place during the Holocene, I fear that they are contaminated by Bond events, which do not constitute a cycle, and many of them are of a clear solar origin.

      I have been looking for climatic effects of this putative lunisolar tidal cycle during the Holocene and what I have found essentially coincides with the ~ 1500 year oceanic cycle. This cycle would have gone from a warming cycle during the glacial period to a cooling cycle during the Holocene undergoing at the same time a phase shift, so it is now cooling at the lows of the previous cycle. If true, the last event of the ~ 1500 year cycle took place during the Little Ice Age, contributing to this very cold period.

  54. I have also noted that is the 2013 blog post cited above that the DO events continue to be seen, though at much reduced levels, in the Holocene temperature. I have even cited a estimate of when the next D-O event might start – my best estimate is about 2160.

  55. P.S. Javier, Thank you for you wonderful article on the possible initiation mechanisms for DO events!

  56. Javier wrote:
    “Solar cycles of ~1500 years are unknown. Orbital cycles of ~1500 years are not widely accepted..”

    Only due to a dearth of diligence and scrutiny, and degrees of confirmation bias.

  57. “….the 1470-year pacing and the triggering mechanism for D-O oscillations.”

    This correlates to an abrupt and unexpected change in North America, where the trend believed to be orbital control (cooling) is interrupted and turns to warming/drying trend 1,600 ybp. (Lachniet 2014, Steponaitis_2015).

  58. I have a different take on D-O events.

    The Achilles heel of an ice age world is albedo. If you can darken the ice, you get rapid warming:

    Modulation of Ice age via Albedo:

    And Fischer demonstrated that all D-O events were closely liked to fire combustion products:

    Millennial changes in North American wildfire activity:

    And now you have all the conditions required for a D-O warming event. If there is a continent-wide conflagration in Asia, then the northern ice sheets will get covered in soot and reduce in albedo, causing a sudden melting and warming. A D-O warming.

    But since this is only a one-off coating of soot, the ice sheets will eventually shed their contaminant, albedo will rise, and the world will cool again. A D-O cooling. And it will take a few thousand years before the forest fuel-load is large enough for another continent-wide conflagration, and another D-O event.

    And Antarctica appears out of synch in teh record, because the lower snowfall there means the gas-age of the Antarctic ice is anything up to a thousand years in error, in comparison to Greenland.


    • Ralph,

      You mistake effect for cause. A common problem. The authors that you cite, Fischer et al., 2015, however have it very clear:

      “We find that on orbital timescales soil emissions increased under warmer climate conditions when vegetation expanded northwards into previously ice-covered areas. For millennial-scale interstadial warm periods during Marine Isotope Stage 3, the fire recurrence rate increased in parallel to the rapid warmings, whereas soil emissions rose more slowly, reflecting slow ice shrinkage and delayed ecosystem changes. We conclude that sudden warming events had little impact on soil ammonium emissions and ammonium transport to Greenland, but did result in a substantial increase in the frequency of North American wildfires.”

      It is the warming that causes soil emissions, vegetation expansion, and fires. There is absolutely no evidence for the highly periodic continent-wide conflagrations prior to the D-O interstadial that your conjecture requires.

      By the way, have you seen Tzedakis et al., 2017 that just came out today on Nature?

      It provides very nice support for about every point that I made in the previous article:

      While it leaves albedo and dust where it corresponds:

      “over time, the glacial system accumulates instability that makes ice sheets more sensitive to insolation increases. This instability can be due to any of the following negative feedbacks on ice growth: (i) mechanical instabilities of the ice–bedrock system, enhanced calving and exposure to lower-latitude insolation as ice sheets grow; (ii) a decrease in ice-sheet albedo and an increase in ablation as a result of higher rates of dust deposition as ice sheets expand; and (iii) releases of deep-ocean CO2 as a function of extension of the Antarctic ice sheet over continental shelves.”

      Just a negative feedback factor between others, that makes ice sheets more sensitive to the insolation increases that drive the glacial cycle.

      Tzedakis et al., 2017 also identify what they call caloric whole summer insolation, which is what Huybers 2006 calls integrated summer insolation forcing, a parameter that is more dependent on obliquity than peak 65°N summer insolation. Besides explaining why interglacials take place when they do, it puts to rest the 100 kyr cycle myth.

      • Fischer et all only said that because the prevailing orthodoxy is that greenhouse gasses are the primary feedback agent controlling ice ages. Had they known that albedo is the primary modulation factor, as I have proved, then they would not have confused cause with effect in the manner that they have.

        In reality, albedo-on-ice feedbacks are orders of magnitude greater than CO2 feedbacks, when calculated regionally. And ice sheet melting is most certainly a regional process. So it is Fischer et al who have it back-to-front, as has palaeoclimatology in general. Including yourself, I feel.


      • As you know, Huybers only managed to invoke obliquity into the recent ice age cycle, because he used a home made sea-sediment chronology that has no chronological pegs and appears tuned towards obliquity.

        If the ice core chronology is used, it is apparent that obliquity plays very little part in the process – except every 400 ky when eccentricity is low and precessional insolation greatly reduces (while obliquity does not). Thus obliquity can reset the ice age cycle to the obliquity cycle every 400 ky, and make it appear that it is the primary controlling orbital factor. But it is quite apparent that in between times, the obliquity cycle is just a ghost in the night, passing through the ice age cycle with no effect.

        And even if you want to champion the obliquity cycle, you still have to explain why half the obliquity cycles are missing from the ice age cycle. Why is the climate system selective? (As indeed it is with the precessional cycle.)

        The answer yet again is albedo. Albedo trumps all insolation variation, be that precession or obliquity, and will lead the climate inexorably towards a snowball earth. Except when dust gets on the ice and the albedo is lowered considerably, and then the insolation absorption in the higher latitudes increases by hundreds of w/m2. Not the 4 w/m2 of puny CO2, but by hundreds of w/m2. And now the ice sheets can start their melt, and an interglacial can be initiated.

        The controlling factor in ice age modulation is albedo. And if you look at the problem with that in mind, all these sudden warmings and slow coolings – even in D-O events – are easily explained. Albedo is the key.


      • Ralph,

        albedo is the primary modulation factor, as I have proved

        You have proved nothing of that sort. Your research does not distinguish cause from effect. Albedo/dust fits perfectly well the bill for a feedback contributing factor.

        Fischer et all only said that because the prevailing orthodoxy is that greenhouse gasses are the primary feedback agent controlling ice ages.

        You don’t know why Fischer et al. said what they said. The most parsimonious explanation is to think that they said what they believe to be true as is usually the case in scientific articles. You can’t recruit them to your side based on what you think they think. Fischer et al. 2015 is not
        a supportive citation to your conjecture.

        As you know, Huybers only managed to invoke obliquity into the recent ice age cycle, because he used a home made sea-sediment chronology

        As you know, because I have told you, that argument is untrue, because I get the same result using EPICA Dome C chronology, that is among the best available.
        Tzedakis et al., 2017 show every interglacial of the past 2.6 million years (the entire Quaternary Ice Age) taking place within a window of obliquity above 23.3°
        “The onset of every interglacial occurs during intervals of above-average obliquity (>23.3°; grey shading in Fig. 2)”
        The obliquity invocation is rock solid, unlike the dust invocation.

        you still have to explain why half the obliquity cycles are missing from the ice age cycle.

        I provided an explanation in my previous article. You just didn’t bother to read it. Tzedakis et al. 2017 formulate it in mathematical terms as
        E(Ipeak, ∆t) = Ipeak + b∆t
        where the effective energy E(Ipeak, ∆t) is a function of caloric summer insolation peak Ipeak (a factor dependent on both precession and obliquity), plus the time since the previous deglaciation Δt, times a discount rate b that provides a measure of accumulated instability. An interglacial is produced when the effective energy goes above the energy threshold.
        This explanation has the ability to reproduce the pattern in the record when tested in a Markov chains Bayesian logistic regression and correctly identifies the points at which anomalies are found (MIS 11 and MIS 7c).

        will lead the climate inexorably towards a snowball earth.

        Ridiculous. This is the same as believing CO2 will lead to a runaway warming that will cook us all.

        The controlling factor in ice age modulation is albedo. And if you look at the problem with that in mind, all these sudden warmings and slow coolings – even in D-O events – are easily explained. Albedo is the key.

        Here you just described your problem. You set your mind on your preferred solution before looking at the problem. Then you won’t let evidence against your solution bother you, or will even twist it like you do with Fischer et al., 2015.

        Your dust/albedo conjecture is based on an imperfect correlation, lacks explanatory power for interglacial distribution (happens when it happens), and as CO2 fails to distinguish between cause and effect. Not to mention that it has an insolvable problem to explain 41k interglacials when the world was warmer and had more CO2, and hence much less dust yet a lot more interglacials.

  59. Incidentally, the 1470 cycle is also approximately the Egyptian Sothic cycle.

    Because the Egyptians did not add the 0.25 extra days to the year, the calendar drifted with respect to the seasons. And it took about 1460 years for the seasons to realign (slightly more, with modern calculations).

    Unfortunately this is a calendrical cycle, and not something that can effect the climate.


  60. Hmmm. You comment, rightly so, that the Pacific does not have the same degree of Arctic cooling access as does the Atlantic. Might that point to the Pacific then as a long term heat recharge/discharge driver of stadial/interstadial periods, while the Atlantic has more ability to rid itself of heat fairly regularly? Certainly the equatorial Pacific is far better at climate change via ENSO processes than the equatorial Atlantic. What works on a small time scale may also have much longer oscillations. And the atmospheric response to warming El Niño and Pacific blob heat discharge is rapid while the cooling reverse to La Niña heat recharge is more pulsed. That seems to be a small scale version of what we see in the ice cores.

  61. I would imagine that the D-O events are breakup and thaw events of ice shelves inhibiting the North Atlantic feed to the Arctic Ocean and also effecting the ‘Achilles Heel’ of the North Atlantic overturning. By all reason, if major poleward heat transport to the Arctic is effectively switched off by ice shelves, then the polar see-saw effect would not be present during the cold stadial periods between the D-O events, and both polar temperatures would change in unison.

    • Ulric,

      The problem is explaining how the D-O mechanism generates a regularly paced cycle. There are a lot of possible explanations but almost all of them would generate an irregular oscillation.

      • The one that I referred to earlier may also account for the intermittence, they don’t happen at every step.

  62. If, as you say, this pattern, the “D-O,” only occurs during “glacial” periods, and instead it may have “transformed into the 1500 year oceanic cycle,” what then would you expect the next human lifetime of climate change/stability/instability to look like?

    • Interglacial climate is a lot more stable than glacial climate. Late Holocene climate is governed by the continuous decline in insolation forcing from Milankovitch orbital changes that have produced the Neoglacial period that started around 5000 years ago and culminated in the Little Ice Age around 350 years ago. Superimposed over this trend we observe the effects of millennial cycles from solar variability and oceanic variability that increase the cooling and are followed by recovery. The Little Ice Age was the coldest period in the Holocene, due to the Milankovitch trend and the coincidence of the lows of all the main millennial cycles.

      For the last 350 years the world has experienced a recovery from the Little Ice Age, helped in the last 70 years by the warming produced by the increase in greenhouse gases. Over the next 100 years natural warming should peak, and greenhouse gases increase should also peak due to fossil fuel depletion and energy transition. Barring significant volcanic activity we should look to a warm stable climate, very much like the climate during the Roman warm period. The cooling trend should return in 200-300 years and become a significant problem for future generations in about 500-600 years, when the next low in the millennial cycles is expected.

      There is an increased probability that glacial inception, the time when continental ice starts to grow, might take place in about 2000 years, around 4000 AD. This is too far into the future to be really a concern for us.

      • Thank you for this, I’ll be thinking about it for a while.

      • Barring significant volcanic activity we should look to a warm stable climate, very much like the climate during the Roman warm period.

        Bring it on! :)

        However, just wondering, should governments be considering implementing a “Volcano Tax” to discourage volcanoes from erupting?

      • “the time when continental ice starts to grow, might take place in about 2000 years, around 4000 AD. This is too far into the future to be really a concern for us.”
        If something doesn’t change our technological trajectory, in 2000 years we will be genetically another species.

      • Ulric Lyons

        My model which hindcasts previous Solar Minima with precision, shows a Super Solar Minimum from the 2090’s lasting about 50 years, and another similarly long Solar Minimum from around 2200 AD.

      • “My model which hindcasts previous Solar Minima with precision”

        Have you posted it anywhere? I would like to take a look at your model. There is only two or three solar grand minima taking place outside the lows of the ~ 1000 and ~ 2400 year solar cycles during the past 11,700 years, and no low in these cycles is going to take place for the next 500-600 years, so a priori I would consider the probability of a grand solar minimum before 2400 AD as very low, and the probability of having two as exceedingly low.

      • Ulric Lyons

        Yes I posted it a few times on WUWT. If you could email me (address is on my LinkedIn public profile) I will send you a full list of start dates and lengths of solar minima from 4700 BC according to the model.
        Here is what an analysis of shorter cycles than the two you refer to shows for the coming centuries:

      • Ok, I see. It is a simple decomposition of the data by cycle analysis.

        A few comments about that talk:

        230 years and 208 years is not the same cycle. Over a few cycles the difference becomes too large to attribute to dating error.

        Where is the cooling predicted? The world is clearly not cooling.

        The 208 yr de Vries cycle is modulated by the ~ 2400 yr Bray cycle. Look at letter d in the following picture:

        We are already at a time when the amplitude of the de Vries cycle is low and its climatic effect almost undetectable. For about 1000 years the de Vries cycle should be muted.

      • Personally I don’t subscribe to the idea of long cycles modulating each other, and regard anything beyond the sunspot cycle itself, as periodic and quasi periodic events that do not constitute cycles at all. Solar minima occur on average roughly every ten solar cycles, but that doesn’t create a sine wave like cycle of solar activity of ~108yrs that can be modulated by another cycle. The same with de Vries, it’s not not a sine wave that can be modulated by other cycles, it’s quasi periodic events. And when a long solar minimum occurs, there’s nothing else happening to phase cancel or ‘mute’ it.

  63. Off-the-wall comment, the sudden rise and slow decay graph looks like what you see with dissipative structures.

  64. Reblogged this on Climate Collections.