Nature Unbound VII – Climate change mechanisms

by Javier

Climate variations that alter the angular momentum of the atmosphere modify the speed of the Earth’s rotation, which affects the length of day (LOD). Alterations in LOD integrate different climate-affecting phenomena, and can anticipate turning points in climate.

Several pathways and feedback mechanisms have been identified that carry and amplify the signal produced by solar cycles. The stratospheric top-down mechanism relies on the quasi-biennial oscillation to affect the northern hemisphere winter climate. A bottom-up mechanism acts mainly in the Pacific Ocean, through changes in SST and cloud cover.

The existence of an ice-ocean-atmosphere ~ 60-year oscillation of unknown origin, might explain a significant part of the observed climate variability.


The Holocene prior to 1950 underwent episodes of profound and abrupt climate change that significantly altered the vegetation of entire ecozones at times of very modest GHG changes. This Holocene variability was reviewed earlier (Part A, and Part B). Thus, besides GHGs and volcanic eruptions, other poorly identified climate change mechanisms must be at work. Proxy analysis has allowed the identification of several climate cycles, some of solar origin (Bray, Eddy, and de Vries cycles), and one of non-solar origin (1500-year cycle). The mechanisms by which they act on climate are poorly understood, and additional mechanisms producing non-cyclical climate changes must also exist.

Several climate change mechanisms have been thoroughly reviewed elsewhere and will not be reviewed here. The effect of GHG concentration changes in the atmosphere is postulated as one of the main mechanisms for climate change, since these gases absorb and emit in the IR band (Hansen et al., 2007). Despite intense efforts, the magnitude of this mechanism’s contribution to climate change is still uncertain. The effect of volcanic eruptions on global climate is due to the absorption and scattering of radiation by sulfate aerosols produced by the vast amounts of sulfur dioxide injected into the stratosphere during strong volcanic eruptions. While they have a high latitude surface warming effect in the Northern Hemisphere winter by warming the stratosphere and disrupting its circulation (Robock and Mao, 1992), they have a stronger surface cooling effect in the lower latitudes and tropics during spring and summer, that can last for a few years (Robock, 2000). Surface cooling is because the sulfate aerosols are more efficient at scattering incoming solar radiation than absorbing Earth’s surface radiation. The aerosols participate in the destruction of ozone through their interaction with anthropogenic chlorine, and in the reduction of atmospheric water vapor (Soden et al., 2002). There is also speculation that volcanic eruptions might trigger or imitate El Niño conditions through their effect on trade winds, partially ameliorating the cooling effect.

Length-of-day and climate

Our capability to measure very slight fluctuations in the speed of rotation of the Earth, that result in micro-second changes in the length-of-day (LOD), has produced some interesting evidence on how climate-related phenomena affect the rotation of the planet. The rotation of the Earth is being constantly slowed by the friction of the tides with the ocean bottom, but once this secular increase in LOD is accounted for, excessive variations of the order of 1 millisecond in LOD are taking place in a scale from hours to decades. The excessive LOD (∆LOD) has been decreasing during the last forty years (figure 90 a), which is the opposite trend to the secular deceleration of the Earth. This multi-decadal decrease in ∆LOD (rotation increase) is attributed to tiny differential rotation in the Earth’s core associated with the geomagnetic field. Considering the Earth a closed system, the conservation of the angular momentum requires that any change in the angular momentum of the solid Earth is matched by an opposite change in the angular momentum of the fluid Earth.

The evidence shows that atmospheric angular momentum (AAM) changes are responsible for LOD changes at certain time scales, but not others. Two mechanisms are proposed to explain the imposed torques that transfer the angular momentum between the atmosphere and the solid Earth. One is due to surface wind tangential stresses across the surface, causing friction torques. The other one is due to mountain torques caused by surface pressure variability near areas of high topography.

Figure 90. Variation of LOD since 1981. a) From top, excessive LOD time data with its decadal trend (T9), components of period between 500 and 2000 days (T6-T8), between 100 and 500 days (annual and semiannual components, T4-T5), and less than 100 days (T1-T3). Four lower curves shifted for convenience, but all in same vertical scale. b) Fourier amplitude spectrum of the excessive LOD time series between 1981 and 2012. The dotted line is the 95% significance level. Source: S.-H. Na et al., 2013. J. Astron. Space Sci. 30, 1, 33-41.

The variations in LOD can be subdivided according to their periodicity (figure 90; Na et al., 2013). The annual (T5) and semiannual (T4) seasonal components match corresponding wind signals in the troposphere and stratosphere that peak 6 months out of phase and are of stronger amplitude due to Northern Hemisphere jets during the boreal winter, while the Southern Hemisphere winter peak is of lower amplitude. The long period band (500-2000 days; T6-T8, figure 90) corresponds in its biannual component to the quasi-biennial oscillation, resulting from the reversal of the zonal winds in the tropical stratosphere, while the 3-4-year component matches the ENSO signal (figure 91; Haas & Scherneck, 2004). During periods of El Niño, the tropospheric zonal winds have westerly anomalies. At the peak of the westerly anomaly period, the globally integrated AAM is notably strong, driving a slowing of the Earth’s rotation. During the 2015-16 winter season, El Niño produced a LOD excursion reaching 0.81 ms in January 2016.

Figure 91. Excess in length of day and El Niño Southern Oscillation. Blue curve, left scale: ∆LOD in milliseconds, long-term detrended (minus T9) and seasonal removed (minus T4-T5). Data from IVS, International VLBI (Very Long Baseline Interferometry) Service for Geodesy & Astrometry, treated as described in J.M. Gipson & C. Ma, 1999. IERS Technical Note 26. Red curve, right scale: Multivariate ENSO index (MEI). There is a clear correlation between the two time series and both show the ENSO events during the 23 years period. Source: R. Haas & H.-G. Scherneck, 2004. IVS 2003 Annual Report.

In 1976, Lambeck and Cazenave reported on the similarity between the trends of numerous climate indices for the past two centuries and changes in ∆LOD, in particular surface temperature and pressure, were related to wind strength. They concluded that periods of increasing zonal winds correlate with an acceleration of the Earth while periods of decreasing zonal circulation correlate with a deceleration of the Earth. They found a lag of 5-10 years in the climatic indices. Their result has been reproduced multiple times, and an example is shown with SST and ∆LOD (figure 92; Mazzarella, 2013). Lambeck and Cazenave considered the wind changes to be too small to account for the change in ∆LOD, and pointed instead that both might share a common origin. They ended with an interesting prediction, as the article was written after several decades of decreasing temperatures:

“if the hypothesis is accepted then the continuing deceleration of [speed of rotation] for the last 10 yr suggests that the present period of decreasing average global temperature will continue for at least another 5-10 yr. Perhaps a slight comfort in this gloomy trend is that in 1972 the LOD showed a sharp positive acceleration that has persisted until the present…”

As they suggested, 4 years after the 1972 sharp decrease in LOD took place, current global warming started, coinciding with the publication of the article. So, the gloomy cooling trend was substituted by what to some is an even gloomier warming trend. Except for the short interval 1987-94, ∆LOD decreased from 1972 to 2004, and has been slightly increasing since.

Figure 92. Earth rotation and sea surface temperature anticorrelation. Continuous line, detrended yearly values of ∆LOD with a 5-year running mean smoothing, shifted ahead 4 years. Dotted line, detrended yearly values of Northern Hemisphere SST, from HadSST3 with a 5-year running mean smoothing. Source: A. Mazzarella, 2013. Nat. Sci. 5, 149-155.

The close correlation between SST and the AAM (and LOD) has been known for a long time. The correlation is explained as due to ocean-atmospheric coupling where upwelling and downwelling depend on wind strength, and atmospheric pressure correlates with SST. Salstein (2015), one of the foremost experts in AAM, explains that the atmosphere has been simulated by a large number of models that are driven solely by the temperature of the underlying ocean surface. Based on these models, AAM has been calculated since the late 19th century from available SST data, and checked against LOD estimations based on lunar occultation measurements.

The nature of the postulated common cause that affects LOD and climate remains obscure. As the decadal trend in LOD is attributed to very small changes in the geomagnetic interaction between core and mantle, either internal solid Earth changes or external magnetic influences could be responsible for the effect on climate that accompanies decadal changes in LOD. Given the importance of stratospheric winds in AAM changes and the disproportionate effect of solar variability on the stratosphere, the Sun is a possible candidate to cause changes in the AAM, thus affecting LOD. Le Mouël et al. (2010) reported a close correlation between the amplitude of the semi-annual variation in LOD (∆LODsa) and the 11-year solar activity cycle. The sunspot number, a proxy for solar activity, led by one year and explained ~ 30% of the amplitude of ∆LODsa (figure 93). A correlation without lag was found between the amplitude of ∆LODsa and galactic cosmic rays. ∆LODsa is due mainly to the 6-month out of phase variation in zonal wind intensity caused by the difference in insolation between hemispheres. It is therefore linked to a fundamental feature of the climate system: the latitudinal distribution and transport of energy and momentum, as the Earth equilibrates the net radiative flux distribution balance between the equator and the poles, establishing the equator-to-poles temperature gradient (figure 66).

Figure 93. Modulation of the semi‐annual LOD variation by the solar Schwabe cycle. In blue, long term variation in the amplitude of the semiannual oscillation in LOD. The amplitude of the Fourier coefficient of the 6‐month spectral line of LOD is computed in a 4‐yr centered sliding window. In red, the sunspot record, inverted and offset to the right by one year. Source: J.-L. Le Mouël et al. 2010. Geophys. Res. Lett. 37, L15307.

Solar signal pathways

The Earth’s upper atmosphere and magnetic field form a coupled system with the Sun and geospace (the space inside the Earth’s magnetic field), that is connected by the solar wind. This coupled Sun-Earth system is responsible for the maintenance of life-compatible conditions on the Earth for thousands of millions of years, since without it, the oxygen would have been stripped from the atmosphere by the solar wind. The Sun is the source of nearly all the energy that drives the climate on Earth, but the Sun’s light is only a part of that energy, the other part corresponds to solar particles and fields. The flow of mass, momentum, and energy from the Sun’s interior through the interplanetary medium into the geospace environment is represented in figure 94 (Baker, 2000). Some of the effects of this flow within the coupled system reveal the effect of solar variability on the atmosphere. I have already discussed the effect of the 11-year Schwabe solar cycle on ozone formation and geopotential height (figure 65), that globally affects the Hadley circulation, causing an extension or contraction of the tropics. Let’s briefly review some of the phenomena that are also likely to be involved in the solar variability regulation of the climate.

Figure 94. The geospace environment engine. The flow of mass, momentum, and energy from the Sun’s interior through the interplanetary medium into the geospace environment. Both normal solar wind flows and transient events are indicated. Source: D.N. Baker. 2000. J. Atmos. Sol.-Terr. Phys. 62, 1669–1681.

The quasi-biennial oscillation (QBO) is a most remarkable atmospheric phenomenon and a major determinant, with ENSO, of seasonal and inter-annual weather variability. In the equatorial stratosphere, strong zonal winds circle the Earth. They originate at an altitude of 10 hPa (~ 35 km) and migrate downward at ~ 1 km/month until they dissipate at the base of the stratosphere at 80 hPa (~ 20 km). As the new zonal wind belt originates to replace the downward migrating previous one, it moves in an opposite direction, alternating easterly and westerly winds (Baldwin et al., 2001; figure 95). The QBO is usually defined at 30 hPa, where winds in one direction will start and increase in strength, and then decline and be replaced by winds moving in the opposite direction. The easterly and westerly phases of the QBO alternate every 22-34 months with an average of 28 months, but the periodicity is tuned to the yearly cycle, so the phase reversal occurs preferentially during the Northern Hemisphere late spring. The signature of the QBO in angular momentum, rather than having only a single spectral frequency peak at ~ 28 months, includes two additional spectral peaks at the annual frequency plus or minus the QBO frequency. In a breakthrough at the time, Lindzen and Holton (1968) proposed, and it was later demonstrated, that convection-originated vertically-propagated gravity waves provided the necessary wave forcing (momentum) for the QBO generation and maintenance (figure 95).

Figure 95. Dynamical overview of the QBO during northern winter. The propagation of various tropical waves is depicted by orange arrows, with the QBO driven by upward propagating gravity, inertia-gravity, Kelvin, and Rossby-gravity waves. The propagation of planetary-scale waves (purple arrows) is shown at middle to high latitudes. Black contours indicate the difference in zonal-mean zonal winds between easterly and westerly phases of the QBO, where the QBO phase is defined by the 40-hPa equatorial wind. Easterly anomalies are light blue, and westerly anomalies are pink. The mesospheric QBO (MQBO) is shown above ~80 km, while wind contours between ~50 and 80 km are dashed due to observational uncertainty. Source: M.P. Baldwin et al. 2001. Rev. Geophys. 39, 2, 179-229.

The QBO is a tropical phenomenon that affects the global stratosphere through the modulation of winds, temperatures, extra-tropical waves, meridional wind circulation, the transport of chemical constituents, and the distribution of ozone. One of the most puzzling aspects of the QBO is that it also modulates the Northern Hemisphere Polar Vortex, a persistent, large-scale, mid-troposphere to stratosphere, low pressure winter zone that when strong contains a large mass of very cold, dense Arctic air, and when weak and disorganized allows masses of cold Arctic air to push equatorward, causing sudden temperature drops in ample regions of the Northern Hemisphere.

In a series of seminal articles Karin Labitzke with Harry van Loon (1987; 2006) established that the QBO modulates the effect of solar activity on the stratosphere and the Polar Vortex. With great insight Labitzke, who was aware of the state of the solar 11-year cycle through time, unlocked a problem that had occupied researchers for centuries when she decided to segregate the data on stratospheric polar temperatures according to QBO phase (Kerr, 1987; figure 96). The very low correlation when all the data is considered, becomes very high using the segregated data, and Labitzke became the first to identify a strong sunspot-weather correlation.

Figure 96. The effect of solar activity on winter North Pole stratospheric temperature. A) Dash-dotted line, January-February average temperature at 30 mbar over the North Pole. Solid line, the 10.7 cm solar flux, a measure of solar activity proportional to the number of sunspots. A correlation cannot be seen. B) Dash-dotted line, same as in A, but only for the years with QBO in west phase (squared in A). Solid line, same as in A. The correlation becomes obvious. East phase QBO values show anti-correlation (not shown). Source: R.A. Kerr. 1987. Science, 238, 479-480.

The data segregation, pioneered by Labitzke, has been used very successfully to establish the relationship between phenomena that present phases, like the QBO, solar variability, and ENSO, and their effects on the Polar Vortex, stratospheric sudden warming events, the PDO and the NAO. Northern Hemisphere winter weather forecasts rely on the QBO phase, solar activity level, and ENSO state, and this has been a very active area of research for the past 30 years. The difficulty is great because despite an improving understanding of the physical basis, weather and climate models have problems reproducing a realistic QBO. For example, only 4 of more than 30 models used for the last IPCC report (AR5) had any sort of QBO. However, reanalysis readily displays the statistical association between the QBO phase and solar activity with stratospheric temperature and geopotential height (figure 97).

Figure 97. The effect of QBO phase and solar activity on Northern Hemisphere winter stratospheric temperature and geopotential height. a) Composite December-January 30 mbar temperature anomaly (°C, 1981-2010 baseline) for seven QBO east years. The situation corresponds to a disorganized polar vortex with more frequent cold Arctic surface air incursions at lower latitudes. b) Same as in a, for five QBO west years. A well-organized polar vortex keeps Arctic air trapped underneath. c) Composite January-March 500 mbar geopotential height anomaly (m, 1981-2010 baseline) for eighteen solar minimum years. A high winter North Pole geopotential is associated to a negative phase of the Arctic Oscillation. d) December-February correlation index between solar index and geopotential height for the 1980-2014 period. High solar activity correlates with low geopotential height over the Arctic. Source: NCEP/NCAR Reanalysis.

The current understanding, supported by observations, reanalysis, and modeling, is that the energy and momentum for the generation and maintenance of the QBO, and the stratospheric effects of the solar cycle and ENSO are provided by different kinds of gravity waves that originate from convection and weather phenomena in the tropics and propagate vertically (figures 95 & 98). Although the stratospheric effects propagate globally and affect both polar annular modes, the geographic asymmetry with most land masses and mountain ranges in the NH, creates hemispheric asymmetry. Planetary-scale Rossby waves that originate at northern mid-latitudes propagate vertically and reach the stratosphere, and the state of the stratosphere determines what happens next with those waves.

The QBO, solar activity, and ENSO act as gate keepers by determining the conductivity of the stratosphere to planetary waves. Combinations of these three factors during the winter cause a constructive or destructive interference with the vertical planetary waves, and in the first case the waves are deflected poleward transmitting heat and momentum to the stratospheric North Arctic Mode and Polar Vortex where they break (figure 98). This selective interaction with planetary waves maintains and even enhances tropical stratospheric anomalies, due to changes in solar activity, as they migrate poleward in the NH and downward to the polar troposphere, during certain winters. On the surface they determine the state of the dominant mode of variability, the Arctic Oscillation, and extend their influence to the North Atlantic Oscillation.

Figure 98. Summary of proposed top-down solar variability effects on climate. Only the Northern Hemisphere is represented, with the left and right halves showing the differences between summer and winter. The effects of solar wind induced magnetic and/or electric coupling, and the effects of cosmic rays are still quite unknown and thus not considered. Energetic particle precipitation at the pole produces odd Nitrogen and Hydrogen species in the upper atmosphere, that are more efficiently transported downward by the winter stratospheric vortex, reducing polar ozone levels. UV solar irradiation, variable with the solar cycle, is responsible for the ozone layer and its temperature gradients. Different types of tropical waves (orange) originating from convection, are responsible for the creation and maintenance of the Quasi-Biennial Oscillation (QBO), that together with the Brewer-Dobson circulation is responsible for the poleward transport of ozone. The position of the Tropical Jet Stream is determined by the Hadley circulation, while the strength and position of the Jet Stream and the Polar Night Jet depend on the strength of the Polar Vortex. Depending on stratospheric conditions, planetary-scale Rossby waves (red) can be deflected during the winter, causing stratospheric warming and a weakening of the Polar Vortex. The Polar Vortex determines the winter state of the Arctic Oscillation (AO), which strongly influences the North Atlantic Oscillation (NAO). Solar activity level, through its effect on stratospheric conditions, influences Northern Hemisphere winter weather far more than its small change in irradiation suggests. The ITCZ, the Inter-Tropical Convergence Zone, is the climatic equator. ENSO, El Niño Southern Oscillation.

While the East and West phases of the QBO have an opposite influence in modulating the effect of solar activity (figure 99), it is the easterly phase of the QBO in combination with low solar activity that shows the larger departure from average conditions. In QBOe winters, during low solar activity, the polar geopotential height is higher, polar stratospheric temperatures are higher, sudden stratospheric warming events occur earlier, the Polar Vortex is more frequently weaker and disorganized, the polar Jet Stream forms meanders that extend into lower latitudes, there is a higher frequency of blocking days, and the AO and NAO tend to be in negative phase (figure 99). This results in winters that are colder in mid-high Northern Hemisphere latitudes. Meteorologists have learned that NH winters with QBOe and low solar activity (like 2017-18 winter) tend to be cold and with more snow, especially in non-La Niña years, unless a recent stratospheric-reaching volcanic eruption interferes and produces a warmer winter.

Figure 99. Conceptual model of potential drivers of winter Jet Stream and NAO variability. A red arrow indicates a strengthening of the target box, while a blue arrow indicates a weakening. NAO can be used as a surrogate for jet stream variability. Arrows are not proportional to strength or confidence attached to the potential forcing. The main drivers of winter jet stream and NAO variability are believed to be the QBO, solar activity, ENSO, and Autumn Eurasian snowpack. Tropical volcanic eruptions can strongly interfere with the other factors driving a stronger vortex and positive NAO. Source: R. Hall et al. 2015. Int. J. Climatol. 35, 8, 1697-1720.

Given the complexity of the solar signal transmission through this indirect pathway, that is both conditional and seasonal, we do not have yet a good quantitative understanding of the mechanism. A further complication comes from the inability of most models to include or realistically reproduce stratospheric phenomena. However, the qualitative knowledge is solidly grounded in observation, reanalysis, and modeling (Baldwind & Dunkerton, 2005; Gray et al., 2010). During solar grand minima, solar activity gets stuck in low mode, and the frequency of cold winters in the NH multiplies, although warm winters can still occur, especially during QBOw phases. A significant deviation towards AO/NAO negative conditions is accompanied by a general decrease in winter temperatures and an increase in snow precipitation, that result in glacier advances. These were the conditions observed during the Maunder period of the Little Ice Age that have been reproduced in models with a clear solar attribution (Shindell et al., 2001).

A complementary pathway for the solar signal has been described for the rest of the solar spectrum that reaches the ocean surface, warming it (Meehl et al., 2009; figure 100). It has been shown to act mainly on the Pacific Ocean, which has the largest oceanic tropical surface. In the relatively cloud-free areas of the subtropics this “bottom up” mechanism determines the amount of evaporation, and by increasing moisture transport, cloud cover and precipitation at the convergence zone at times of higher solar activity, it expands the Hadley circulation and increases trade winds. The strengthened atmospheric circulation and moisture creates a feedback that enhances warm humid air subsidence at the sub-tropics further reducing cloud cover and enhancing the effect. The tropical effect is transmitted to the stratosphere by gravity waves, and carried to mid-latitudes by the Brewer-Dobson circulation. The increase in trade winds associated with the expansion of the Hadley circulation produces a negative anomaly in Eastern Pacific sea surface temperatures a year before the solar peak, that transforms into a positive anomaly with a two-year lag to the solar peak (Meehl et al., 2009).

Figure 100. Summary of proposed bottom-up solar variability effects on climate. Only the Pacific during the northern-winter is represented. In less clouded subtropical areas, peak solar activity increases evaporation. The enhanced moisture is transported by trade winds to convergence zones increasing precipitation, and strengthening Walker (not shown) and Hadley circulations. Intensified trade winds increase equatorial ocean upwelling reducing equatorial SST and driving a cloud reduction, through enhanced subsidence, that acts as a positive feedback similar to La Niña conditions, allowing more solar radiation to reach the surface. The Hadley circulation expands poleward increasing the area of the tropics. After the solar peak the eastern equatorial surface transitions to higher SSTs a couple of years later. The effect is stronger during the northern-winter. ITCZ, Inter-Tropical Convergence Zone, the climatic equator.

As we have seen, there are several pathways by which the solar signal is transmitted to the atmosphere-ocean coupled system and amplified through several feedback mechanisms, affecting climate (Roy, 2013; figure 101). Although the solar changes are small, the amplification energy is provided by the climate system. The pathways are complex, involving some of the lesser known climate phenomena, and act in a phase, seasonal, and latitudinal dependent way, often with opposite results. This is why the solar variability signal, whose effect can be seen so clearly in paleoclimatic records, is so hard to see in real time. The existence of more than one pathway also multiplies the signal, and further enhancement is attained through the different lags that allow an accumulation of the effect.

Figure 101. Flow chart of the Sun’s influence on climate. The three major climate variabilities, solar, QBO and ENSO are shown with oval outlines, whereas, the major circulations, responsible for modulating the effect of major variabilities are shown by non-rectangular parallelograms. The climatic effects are shown in blue-line boxes, with the direction of change shown by + (for increase) or − (for decrease). Source: I. Roy. 2014. Int. J. Climatol. 34, 3, 655-677.

The 50-70-year oscillation and the Stadium Wave hypothesis

The existence of a multidecadal mode of climate variation was first detected by Folland et al. (1984) in global SST and night marine air temperature records, and later correlated to precipitation records in the Sahel (Folland et al., 1986). This multidecadal oscillation was isolated by Schlesinger and Ramankutty (1994) in the global mean instrumental temperature record, as a 65-70-year northern hemisphere periodicity, and attributed to internal variability of the coupled ocean-atmosphere system. It was termed the Atlantic Multidecadal Oscillation (AMO) by Kerr (2000).

In the following years the 50-70-year oscillation was observed in North Atlantic sea level pressure and winds (Kushnir, 1994), North Pacific and North American temperatures (Minobe, 1997), length of day and core angular momentum (Hide et al., 2000), fish populations (Mantua et al., 1997: Klyashtorin, 2001), Arctic temperatures and sea ice extent (Polyakov et al., 2004), ENSO events relative frequency (Verdon & Franks, 2006), and global mean sea level (Jevrejeva et al., 2008).

Most of these records display also a ~ 20-year periodicity that is apparent in Greenland δ18O ice core data (Chylek et al., 2012). Differences between this periodicity, that is most apparent at mid-latitudes subsurface temperatures, and the 50-70-year oscillation, most apparent at high latitudes deep water salinity levels (Frankcombe et al., 2010), preclude a direct harmonic relation between them. Additionally, proxies indicate the ~ 20-year periodicity was more intense during the LIA, while the 50-70-year oscillation appears more intensely in 20th century records, and might not have been present, at least with that interval, during the LIA (Gray et al., 2004).

It is generally believed that the 50-70-year oscillation originates from internal ocean-atmosphere variability, rather than being externally forced or random generated. There remains the possibility that multidecadal external solar and tidal forcings set in motion the transfer of heat between different oceanic basins, and the 50-70-year oscillation could be an emergent temporal resonance from the intrinsic delays in the oceanic and atmospheric heat transmission. In this regard, the Bjerknes hypothesis establishes that hemispheric anomalies in the transport of heat by the atmosphere and the oceans should be of equal magnitude and opposite sign (Bjerknes compensation). The Bjerknes compensation has not been measured in nature due to our inability to properly sample heat transport by the oceans, but interestingly the Bergen climate model, when reproducing the Bjerknes compensation under constant forcing, generates a 60-80-year periodicity reminiscent of the AMO (Outten & Esau, 2017).

Whatever its cause, a climate quasi-periodicity leads to a climate quasi-predictability. Not as good as deterministic predictability, but much better than chaotic unpredictability. Divine and Dick, in their 2006 study of the historical variability of sea ice edge position in the Nordic Seas, correctly identified the effect of the 50-70-year oscillation over any putative anthropogenic effect, and ended with the conclusion that “during decades to come, as the negative phase of the thermohaline circulation evolves, the retreat of ice cover may change to an expansion.” It must have taken courage to predict a sea ice expansion in 2006, when essentially everybody else was predicting a sea ice collapse, yet since 2007 Arctic sea ice has been showing a, still non-significant, modest growth in September extent.

In her 2012 PhD thesis, Marcia Wyatt developed a hypothesis on the dynamic transfer of a climate signal between the different ocean basins, Arctic sea ice, and the atmosphere by the 50-70-year oscillation, that she termed “the Stadium Wave.” The hypothesis neatly links all the different manifestations of the 50-70-year oscillation, accounting for their lags, and produces a complete set of “quasi-predictions” that should be good for as long as the oscillation maintains its periodicity (figure 102; Wyatt & Curry, 2014). Wyatt and Curry, 2014, is one of the few articles (with Divine & Dick, 2006) that correctly predicted the current pause in Arctic sea ice melting at a time when the data suggested the opposite: “this [sea ice decline] trend should reverse… Rebound in West Ice Extent, followed by Arctic Seas of Siberia should occur after the estimated 2006 minimum of West Ice Extent and maximum of AMO” (Wyatt & Curry, 2014).

Figure 102. The 50-70-year oscillation and the Stadium Wave hypothesis. a) Simplified Stadium-Wave Wheel cartoon showing a 60-year cycle from 1976 to 2036. Red color indicates the high warming phase, and blue color the low warming/cooling phase. AMO, Atlantic Multidecadal Oscillation. AO, Arctic Oscillation. NAO, North Atlantic Oscillation. PDO, Pacific Decadal Oscillation. LOD, Length of Day. NHT, Northern Hemisphere Temperature. Modified from: M.G. Wyatt & J.A. Curry. 2014. Clim. Dyn. 42, 9-10, 2763-2782. b) Length of Day in milliseconds, daily data (grey) and long-term average smoothed (black). Source: IERS EOP. c) Atlantic Multidecadal Oscillation in °C detrended, monthly data unsmoothed (grey) and long-term average smoothed (black). Source: NOAA. d) Northern Hemisphere Temperature in °C anomaly (1961-90 baseline), monthly data (grey) and long-term average smoothed (black). Source: Hadley Climate Research Unit. e) Arctic Sea Ice extent in million km2, September data (grey) and long term average smoothed (black). Source: 1962-1978, M.A. Cea Piron & J.A. Cano Pasalodos. 2016. Rev. Clim. 16. 1979-2017 NSIDC. f) Sea Level rate of change in mm/yr. Average of Church & White 2011, Ray & Douglas 2011, and Jevrejeva et al. 2014. Source: S. Dangendorf et al. 2017. PNAS. 114, 23, 5946-5951. Orange and blue bars are inflection points when a phase might have changed. A decrease in Sea Level rate is anticipated by the hypothesis.

The most important consequence of the 50-70-year oscillation is that ~ 30 year warming and cooling phases and their associated effects on pressure, winds, precipitation, sea ice, and sea levels, should be properly accounted for by any global climate theory and models. It is clearly not the case of the leading CO2 hypothesis of climate change and the models that support it, where the last cooling phase of the oscillation was assigned to anthropogenic aerosols, and the last warming phase to anthropogenic greenhouse gases, leading to a completely unexpected, albeit predictable, warming pause 30 years later.



1) Excessive variation in the speed of rotation of the Earth, as measured by the length of day (∆LOD), is affected by alterations in the angular momentum of the atmosphere due to changes in tropospheric and stratospheric winds that are driven among other things by ENSO and insolation variations.

2) ∆LOD can be considered a proxy for zonal wind strength that acts as a leading indicator for major climatic turns.

3) The solar cycle, Quasi-Biennial Oscillation, and ENSO, determine the status of the ozone layer in the winter Northern Hemisphere stratosphere and through it, the status of the Polar Vortex and winter weather.

4) The solar cycle also affects SST and Hadley circulation strength through a bottom-up mechanism mediated by evaporation/precipitation and wind-induced upwelling.

5) A 50-70-year oscillation has been observed in multiple climate-related phenomena that can explain a significant part of climate variability. The Stadium Wave hypothesis proposes that dynamic energy-transfer through different ocean-atmospheric-ice compartments can explain the timing of climatic changes.


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

References [Bibliography ]

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68 responses to “Nature Unbound VII – Climate change mechanisms

  1. Reblogged this on Climate Collections.

  2. You can eliminate the effect of a 50-70 year cycle by looking at the average trend in the last 50-70 years, nearly a degree of warming, which I show here together with a clue to its primary cause.
    75% of our CO2 addition has occurred since 1950, and at an increasing rate, adding ~1.5 W/m2 of forcing in this period. This amount of forcing change accounts for the warming when using 2 C per doubling, as the rough scaling in the graph of 1 C per 100 ppm illustrates.

    • According to Phil Jones the warming rates for the periods 1860-1880, 1910-1940 and 1975-2009, are similar and not statistically significantly different from each other.

      If what you say is correct and a new and strong forcing has been added to the last period, this should not be the case.

      • Jimm Macfarland

        We must not look away from the natural processes that has established the past climate variability. Including the recent ~30year near equal atmospheric warming periods, as you present in reply to JD.

      • You also must not look away from other data and the longer record.

        A – Do you agree that according to the global temperature record used by the IPCC, the rates of global warming from 1860-1880, 1910-1940 and 1975-1998 were identical?

        21 years:
        1860 to 1881 – .11 ℃ per decade
        1910 to 1941 – .13 ℃ per decade
        24 years:
        1975 to 1999 – .19 ℃ per decade
        36 years:
        1975 to 2011 – .18 ℃ per decade
        43 years:
        1975 to 2018 -.18 ℃ per decade

    • “You can eliminate the effect of a 50-70 year cycle by looking at the average trend in the last 50-70 years,”

      Particularly nonsensical when there are multiple cycles present. Cf.

      • What combination of cycles leads to a steady ramp of 1 degree in 60 years?

      • Cucumber sandwich

      • jim d. warm pdo coinciding/partially overlapping with warm phase of amo would be enough for northern hemisphere increase. there also appears to be a case for el nino/la nina periods to be in favour of one or the other being particularly strong for long periods.

  3. The forcing has raised the 30-year temperature a degree above the long-term mean climate. It takes a lot of forcing to get to that amplitude. It’s not the trend, it’s the amplitude that is unusual.

    • There is no long-term mean climate.

      • The temperature record prior to GHGs would represent an unperturbed mean. There was a negative trend in that over the past millennium, but only a few tenths of a degree, which is relatively stable compared to the last century.

      • There is no temperature record prior to GHGs.

        We don’t really know how much cooling took place over the past millennium. There is no way to know if it was a few tenths of a degree.

        The past millennium included the Medieval Climate Anomaly, a warm period, and the Little Ice Age, the coldest period in the Holocene, so it was anything but relatively stable.

        You talk nonsense.

      • You dismiss paleoclimate results from the largest observational study yet, but your whole series is about paleoclimate. How does that happen?

      • I do not dismiss paleoclimate studies. I dismiss your comparison. You cannot compare precise, frequent, temperature recordings at many places, homogenized to produce an average anomaly (not temperature), with an assortment of proxies that reflect local conditions and record something that only indirectly and tentatively can be related to temperature.

        You are the one that doesn’t understand the nature of what you discuss.

        There is no way to relate what the proxies say and what the termometers say in a meaningful way. At most we can identify periods of warming and cooling according to local proxies from different places, and compare those periods within each proxy.

      • The PAGES2k paleo reconstruction is given in terms of 30-year global averages, and yes you can get 30-year global averages from thermometer data too. The current 30-year average temperature is approaching 1 degree warmer than the millennium average and trending upwards as I already showed above. You dismiss this plot because the result is inconvenient to you.

      • You cannot compare precise, frequent, temperature recordings at many places, homogenized to produce an average anomaly (not temperature), with an assortment of proxies that reflect local conditions and record something that only indirectly and tentatively can be related to temperature.

        Is there a reference in support of this claim?

      • Dear lord, Jim D has the nerve to put up Mann’s phony hockey stick graph? Has anyone told him about that FTP directory labeled SECRET? Or about short-centered principle components analysis? Or about strip-bark pine tree rings?

      • PAGES is an ongoing international project that combines proxies to increasingly improve paleoclimate reconstructions. That its latest results PAGES2k reaffirm Mann’s trend of the last millennium with much reduced error bars is surely a hard thing for the HS-bashers to take, but it does. The skeptics need to eat their words and accept that the temperature does resemble a hockey stick after all. The trend of the last century is twenty times and in the opposite direction to the trend in the last millennium or two.

      • “The trend of the last century is twenty times and in the opposite direction to the trend in the last millennium or two.”

        Then it should be relatively straight-forward to compare the proxies used to reconstruct temp prior to instrumentation, with the same proxies during the instrumental period.
        It should also be relatively straight-forward to use the 30 year mean of the thermometer series as a comparison.
        Yet you do neither.
        Without checking, I would suspect your “proof” graph would look significantly different if you did either – certainly, we already know “Mike’s nature trick” of removing inconvenient proxy data that is “obviously wrong” is not below most climate scientists ethics.
        PAGES2K (2nd edition, after first was withdrawn due to mistakes pointed out within days be he-who-must-not-be-named – this despite the multitude of contributing authors and a peer review) is almost as bad as MBH9x – both seem to have been constructed in reverse (the ol’ “how do I get what I know is right” trick).

        If you really want to convince people you are right, it takes more than calling them names, or citing dubious papers as authoritative.

      • kneel, the 30-year BEST temperature does look a lot like the red line on that graph.
        What else do you need?

      • Jimd

        Your wood for trees graph would be more interesting if it used the Best temperature series data as far back as it goes and did not include sea temperatures which on a global level are worthless during that earlier period.

        As for land temperatures, do you really believe our ancestors lived in virtually a state of constant cold? Did they hibernate during the winter?

        The manorial records back to the 11th century the extensive written records, the evidence of their farming at higher levels than today, the higher tree lines, do not support this notion you have and there is no evidence of the trend of the last century being twenty times and in the opposite direction as you state.

        The met office used to state that on their web site about the climate constancy for many centuries until man disturbed that equilibrium, but then removed it about five years ago when they admitted it was not as had been believed.

        That was around the time, in 2005, that Phil jones stated that natural variability was much greater than had hitherto been realised.

        I have referenced these sources to you numerous times.

        The pick up in temperatures began around 1690 after a intermittently cold period lasting several centuries, with this cold period topped and tailed by the mwp and the modern warm period


      • Phil Jones needs to write a paper.

      • From Cheng 2014

        In this study, a previously undetected error caused by the low vertical resolution of historical subsurface ob- servations in OHC estimation was diagnosed. When taking the global average, this bias appeared to be cold within the upper 100 m, warm within 100–700 m, and warm when integrated over the whole water column from 0 to 700 m. On a global average, this bias ranged from 10.018 to 10.0258C during the past 45 years. Comparing the long-term change of this bias of ;0.0158C with global warming signals of 0.158–0.28C from 1966 to 2010, we concluded that this bias represents a non- negligible contribution to the global ocean heat content during the past 45 years.

        Other studies have identified sources of uncertainty, in addition to the problems with vertical resolution. Spatial coverage in the 1960s certainly was not as complete as with the most recent ARGO system.

        Anything pre fully rolled out ARGO should be taken with a grain of salt.
        Just a lot of guessing.

      • The source of the graphic is Lijing Cheng. Same guy.

      • tonyb, you seem interested in the BEST temperatures and should take details up with people more familiar, like Mosher. The plot I showed uses the full amount available to WfT, and since it is 30-year averages, it starts 15 years after the data starts and ends that much before the present. Before 1980 the temperature varied within only half a degree, or 1 F, so I don’t think it is so much that the early era is cold as that the late era is really warm after 1980. It really has been a step change in climate terms, and BEST illustrates that, nor is the step done with yet depending on further emissions.

      • He only uses pink crayons. But, he has said 0-100 has cooled since 2000, and he has acknowledged the hiatus.

      • Before Karl, lots of smart people flubbed up the warming hiatus.

        Our studies show that there has been no slowdown in global OHC change since 1998 compared with the previous decade (Fig. 5): – Cheng:

      • A marginal view as opposed to the pause consensus?

      • Cheng also proposed 10 correction schemes to address known biases in the XBT data. Back to an original point. Anything before full implementation of ARGO has marginal value. And in 20 years a new generation will find weaknesses in the current efforts.
        A more valuable contribution would be graphs pre-MWP. Then some comparative analyses could be done. But given the error bars for so far back not likely.

      • I agree that there is no long-term mean climate and found your essay very interesting, but there is a global climate.

        It is curious and perhaps somewhat disconcerting that the essay, a discussion of Earth’s climate, does not address at all the Southern Polar Vortex. Should it be mentioned why a discussion of the Southern Polar Vortex was ruled out within the scope of the essay?

      • why a discussion of the Southern Polar Vortex was ruled out within the scope of the essay?

        The article deals not with Earth’s climate, but with a subset of mechanisms related to climate change, either causal, or consequence. The climate of Antarctica is not dealt with because it is outside the scope, and it would probably require an article by itself. It has been said that Antarctica has such a different and isolated climate with respect to the rest of the planet, that it could well be in a different planet. It clearly does not respond to insolation changes in the same way as the Arctic, it has an ozone hole part of the year, and it has been proposed that responds differently to the increase in CO₂ as it doesn’t show polar amplification.

        I am not very knowledgeable about the climate of Antarctica, so to write about it I would have to study the subject first.

      • PAGES2k is simply perpetuating the Shakun – Marcott et al trick of flattening the Holocene by stirring in dozens of bogus biological proxies. The isotope proxies (ice, sediment) are the only serious ones.

        Meanwhile that MWP which pages2k is trying to bury, shows up alive and well in Africa and Arabia (1/4 of earth’s land surface):

    • Geoff Sherrington

      JimD. Jan 21 10:16
      The proxies are usually calibrated against an instrumental thermometer set.
      Error begets error. Geoff.

      • You have to be careful that a blanket dismissal like that also can’t be said about satellite calibrations. Anyway, if you don’t believe thermometers, just wow.

      • it is usually recommended that anyone citing pages2k pay a visit to climate audit to disabuse them of the notion of its veracity. maybe jimd should pay climate audit a visit.

    • jch

      I do not disagree especially with your graphic at 9.17 back to 1960. Jimd had however posted sea temperatures back to 1860. Would you like to defend those?

      • This is L&O, L, and SST from the Limeys that are available at WfT:

      • Ocean thermometer from the past

        This event was an interruption in the overall warming trend, during which sci- entists think that temperatures dropped by a few degrees in the Northern Hemisphere11 but continued to increase, perhaps even at an accelerated rate, in the Southern Hemisphere12. Bereiter and colleagues report that the mean ocean temperature (which reflects the global ocean, but is weighted towards the Southern Hemisphere) increased substantially during the Younger Dryas, much more than had been estimated: the temperature increase was a whopping 1.6 °C in only 700 years. This is about 1.7 times faster than the ocean is warm- ing now because of global climate change. The reasons for this large warming should be investigated.

        The authors also show that the ocean warmed faster than the atmosphere during the Younger Dryas, and then stopped warming before the atmosphere did. …

      • JCH, if you read the press release from Bereiter et al., 2018, you must have seen that their Xenon/Krypton methodology gives them an estimate of only 0.1°C warming of the oceans during the past 50 years, at an average temperature of just 3.5°C.

        Awful data that paints such a bleak future. Another 0.1°C and we are done.

      • One of the authors explains that at Scripps.

        From one of their graphics, I think:

      • Jch

        By limeys, I assume you mean those nice scientists at the met office?

        You may recall my article on sst’s from 2011

        In the comments you will see contributions from well known met office limey john Kennedy

        Very little of the world had been fully explored in 1860 ajd Even less of the oceans other than a few well used trade routes. Very very little data is used to populate the temperature grid squares.

        Hms challenger provided a scientific insight, but it was over a tiny portion of the watery globe.

        Science does itself no favours when it claims any sort of accuracy over this very fragmented area of temperatures with very little data and much of that collected in a haphazard fashion.
        I can not believe you are defending it back to1860


      • I think they disagree with you.

        But it’s an argument over a pile of stuff that ain’t even a hill of beans.

  4. Another informative post.

    I recently read 238 abstracts/papers by 1011 authors about solar variability and climate. They all were published in 2016 and 2017. None of the authors was named Svensmark, Scafetta or Soon. Given each paper had numerous citations, that means even more authors are involved in research about the relationship between the sun and our planet’s climate.

    In spite of this apparent widespread interest in the solar effects on our climate, it appears solar research is considered a stepchild by the establishment and not given as much respect as the other disciplines.

    There seems to be a disconnect between a not insignificant body of scientific inquiry and the IPCC attention given to it.

  5. Jimm Macfarland

    Another very good post from extensive research. Thank you for your efforts and another highly enlightening post.

  6. Like a torque…

    “This reductionist approach [of government scientists] is misguided since the model [climatists’ General Circulation models] will never be able to be correctly evaluated. To overcome such a paradox, we followed a holistic approach that analyzes the Sun, atmospheric circulation, Earth’s rotation and sea temperature as a single unit (ut unum sint): the arrival on the Earth of fronts of hydrodynamic shock waves during epochs of strong ejection of particles from Sun gives rise to a squeezing of the Earth’s magnetosphere and to a deceleration of zonal atmospheric circulation which, like a torque, causes the Earth’s rotation to decelerate which, in turn, causes a decrease in sea temperature. Under this holistic approach, the turbulence of solar wind and the zonal atmospheric wind behave cumulatively rather than instantaneously, where energy inputs are first conveniently accumulated and then transmitted…”

    (Adriano Mazzarella)

  7. Re Figure 96. QBO west winters with negative AO at sunspot maximum, 1958, 1960, 1970, 1978, 1979. That suggests that weak solar wind strongly dominates over the west QBO and the higher solar irradiance.

  8. I regard this as the most important data correlation in global climate dynamics. The phase reversal occurs because the solar poloidal and toroidal fields change relative phase, and shows that the dominant solar forcing variable must be the solar wind strength. From that frame of reference, it is apparent that stronger solar wind drives a colder AMO, down to at least inter-annual scales, e.g. during the mid 1970’s, mid 1980’s, and early 1990’s.

  9. “Climate is ultimately complex. Complexity begs for reductionism. With reductionism, a puzzle is studied by way of its pieces. While this approach illuminates the climate system’s components, climate’s full picture remains elusive. Understanding the pieces does not ensure understanding the collection of pieces. This conundrum motivates our study.” Marcia Wyatt –

    The stadium wave is at it’s core about synchronous chaos in Earth’s spatio-temporal chaotic flow filed. Ocean and atmospheric indices can be seen as quasi standing waves and are the result of internal resonance in the system that may be randomly triggered by changes in solar activity.

    “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. Anomalous temperatures in the region of the tropical stratopause give rise to changes in the subtropical stratospheric winds, in geostrophic balance with the modified equator-to-pole temperature gradient. This signal then propagates poleward and downward and is amplified by altered planetary wave activity8 before being communicated throughout the depth of the troposphere in the Pacific and Atlantic basins14. This mechanism can also drive changes in tropical lower stratosphere temperatures, which can additionally affect the troposphere15.”

    The details of atmospheric pathways are turbulent and chaotic – and partial atmospheric mechanisms captured by indices are not causal at all but at best are an internal response of the resonant system.

    The key mechanism of decadal internal climate variability is – however – evident. It is caused by changes in surface pressure at the poles. Changes in polar annular modes result in changes in sub-polar winds and gyres in all the world’s oceans and result in changes in all these indices that we like so much.

    None of it is all that predictable in detail – nor has anyone disagregated the anthropogenic component convincingly. The nature of the complex and dynamic system suggests the potential for abrupt climate change as a dynamic response to changes in greenhouse gas concentrations.

  10. A lot of angular momentum transfers to the moon’s orbit or to the earth’s orbit. It’s not a closed system once the earth isn’t a solid sphere.

  11. Great review Javier. Figure 97 c low sun is exactly what we are seeing today:
    Paul Pukite has done an impressive QBO ENSO correlation:

  12. Javier, that is another interesting essay. Thank you.

  13. Judith,
    Have you caught up with Euan Mearns current blog on the GSL position papers on climate change? I think you might find them interesting and I know we would all value any contribution you might make?
    So here are the links with a note from Euan as to what we are trying to do
    There are a group of disgruntled Geos who want the statement withdrawn or amended. So far it has 3231 reads with a little help from Paul Homewood. And we have 190 comments, many lengthy and well-informed. Colin Summerhayes the working group chair has been very active in comments (Polarscientist).

    I appreciate that the main post simply duplicates the Geol Soc statements and is rather turgid. Below are links to three main comment responses:

    I have another post today on same theme covering cosmogenic isotopes that I will cover in a separate email later in the week.

    Howard Dewhirst

  14. Pingback: Nature Unbound VIII – Modern global warming | Climate Etc.