Sea level rise acceleration (or not): Part VI. Projections for the 21st century

by Judith Curry

The concern about sea level rise is driven primarily by projections of future sea level rise.

Observed sea level rise over the last century has averaged about 8 inches, although local values may be substantially more or less based on local vertical land motion, land use, regional ocean circulations and tidal variations.

Projections of future sea level rise can be made in the following ways:

  • Extrapolation of recent trends
  • Semi-empirical approaches based on past relationships of sea level rise with temperature
  • Process-based methods using models

1. IPCC’s 21st century projections

Sea level rise projections (both semi-empirical and process-based methods) are directly tied to projections of surface temperature, which are based upon simulations from global climate models.

The climate model simulations of 21st century climate referenced in the IPCC AR5 are based on more than 30 different global climate models from international climate modeling groups. These simulations are coordinated by the CMIP (Coupled Model Intercomparison Project), under the auspices of the World Climate Research Programme (WCRP).

Chapter 11 of the AR5 describes uncertainties in the model-based projections:

Climate projections are subject to several sources of uncertainty. The first arises from natural internal variability, which is intrinsic to the climate system, and includes phenomena such as variability in the mid-latitude storm tracks and the ENSO. The existence of internal variability places fundamental limits on the precision with which future climate variables can be projected. The second is uncertainty concerning the past, present and future forcing of the climate system by natural and anthropogenic forcing agents such as GHGs, aerosols, solar forcing and land use change. The third is uncertainty related to the response of the climate system to the specified forcing agents. [Section]

Chapter 12 of the IPCC AR5 WG1 report explains the constraints, limitations and uncertainties in the 21st century projections, which assess climate change in response to the emissions scenarios:

“With regard to solar forcing, the 1985–2005 solar cycle is repeated. Neither projections of future deviations from this solar cycle, nor future volcanic RF [radiative forcing] and their uncertainties are considered.” [Section 12.2.3]

“Any climate projection is subject to sampling uncertainties that arise because of internal variability. [P]rediction of the amplitude or phase of some mode of variability that may be important on long time scales is not addressed.” [Section 12.2.3]

Simplifications and the interactions between parameterized and resolved processes induce ‘errors’ in models, which can have a leading-order impact on projections. Also, current models may exclude some processes that could turn out to be important for projections (e.g., methane clathrate release) or produce a common error in the representation of a particular process.” [Section 12.2.3]

A key issue is the uncertainty of sensitivity of climate models to CO2. The equilibrium climate sensitivity is a measure of the climate system response to sustained radiative forcingdefined as the amount of warming in response to a doubling of atmospheric CO2 define.

Equilibrium climate sensitivity is likely in the range 1.5°C to 4.5°C (high confidence), extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence).” “No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies.” (AR5 WG1 SPM, page 14)

The average value of equilibrium climate sensitivity for climate models used in the 21st century projections is 3.2oC, with a range 2.08 to 4.67oC. [AR5 WG1 Chapter 12, Box 12.2] The lower part of the climate sensitivity range is not covered by the global climate models. Figure 1 of Box 12.2 in the AR5 WG1 shows that 11 out of 19 observational-based studies of ECS have values below 1.5oC in the range of their ECS probability distributions.

2.1 Temperature

The IPCC AR4 (2007) made the following projection for near term warming:

For the next two decades, a warming of about 0.2°C per decade is projected.” [IPCC AR4 WG1 SPM, p 12]  [Note: for the period 2011-2030]

At the time of the IPCC AR5, this rate of warming had not been realized, and there was slowdown in warming during the period 1998-2012:

[T]he rate of warming over the past 15 years (1998–2012; 0.05 [–0.05 to +0.15] °C per decade), which begins with a strong El Niño, is smaller than the rate calculated since 1951 (1951–2012; 0.12 [0.08 to 0.14] °C per decade).” [IPCC AR5 SPM, p 5]

Chapter 11 of the AR5 compares the near term climate model temperature projections with observations [Figure 11.25].Figure 11.25 | Synthesis of near-term projections of global mean surface air temperature (GMST). Simulations and projections of annual mean GMST 1986–2050 (anomalies relative to 1986–2005). Projections under all RCPs from CMIP5 models showing the 5 to 95% range of annual mean CMIP5 projections (using one ensemble member per model) for all RCPs using a reference period of 1986–2005 (light grey shade) and all RCPs using a reference period of 2006–2012, together with the observed anomaly for (2006–2012) to (1986–2005) of 0.16°C (dark grey shade). The maximum and minimum values from CMIP5 using all ensemble members and the 1986–2005 reference period are shown by the grey lines (also smoothed). Black lines show annual mean observational estimates. The red hatched region shows the indicative likely range for annual mean GMST during the period 2016–2035 based on the ‘ALL RCPs Assessed’ likely range for the 20-year mean GMST anomaly for 2016–2035

It is seen the observed temperatures between 2007-2012 are at the bottom of the envelope of climate model simulations”

The CMIP5 5 to 95% ranges for GMST (global mean surface temperature) trends in the period 2012–2035 are 0.11°C to 0.41°C per decade. It may also be compared with recent rates in the observational record (e.g., ~0.26°C per decade for 1984–1998 and ~0.04°C per decade for hiatus period 1998–2012).” [AR5 Section]

The AR5 then makes the following projection, based on expert judgment:

[I]t is likely (>66% probability) that the GMST anomaly for the period 2016–2035, relative to the reference period of 1986–2005 will be in the range 0.3°C to 0.7°C (expert assessment; medium confidence). [This range] is also consistent with the CMIP5 5 to 95% range for all four RCP scenarios of 0.36°C to 0.79°C, using the 2006–2012 reference period, after the upper and lower bounds are reduced by 10% to take into account the evidence that some models may be too sensitive to anthropogenic forcing.” [AR5 WG1 Section]

The AR5 concludes:

““However, the implied rates of warming over the period from 1986–2005 to 2016–2035 are lower as a result of the hiatus: 0.10°C to 0.23°C per decade, suggesting the AR4 assessment was near the upper end of current expectations for this specific time interval.” [AR5 WG1 Section]

The author of Figure 11.25 – Ed Hawkins of Reading University – provides an annual update of Figure 11.25. The figure below includes the surface temperature data through 2017.

It is seen that the large El Nino of 2016 has returned the observed temperature curve to near the middle of the envelope of climate model simulations; however the previous large El Nino of 1998 was at the top of the envelope of climate model simulations. The recent data since 2012 continues to indicate that the sensitivity of at least some of the climate models to CO2 forcing is too high.

The IPCC makes the following projections for the 21st century global temperatures:

Increase of global mean surface temperatures for 2081–2100 relative to 1986–2005 is projected to likely be in the ranges derived from the concentration-driven CMIP5 model simulations, that is, 0.3°C to 1.7°C (RCP2.6), 1.1°C to 2.6°C (RCP4.5), 1.4°C to 3.1°C (RCP6.0), 2.6°C to 4.8°C (RCP8.5).” 
[SR5 AR5 WG1 SPM p 20]

Figure SPM.7 | CMIP5 multi-model simulated time series from 1950 to 2100 for change in global annual mean surface temperature relative to 1986–2005, Time series of projections and a measure of uncertainty (shading) are shown for scenarios RCP2.6 (blue) and RCP8.5 (red).

While the near-term temperature projections were lowered relative to the CMIP5 simulations [AR5 Figure 11.25], a note in the caption of Table SPM.2 states:

The likely ranges for 2046−2065 do not take into account the possible influence of factors that lead to the assessed range for near-term (2016−2035) global mean surface temperature change that is lower than the 5−95% model range, because the influence of these factors on longer term projections has not been quantified due to insufficient scientific understanding.” (AR5 SPM, Table SPM.2)

Summary: No account is made in these projections of 21st century climate change for the substantial uncertainty in climate sensitivity that is acknowledged by the IPCC. Hence, there is an internal inconsistency in the IPCC AR5 WG1 Report: the AR5 assesses substantial uncertainty in climate sensitivity and lowered their projections for 2016-2035 relative to the climate model projections, whereas the projections out to 2100 that use climate models that do not include the lower values of climate sensitivity that would produce warming that is substantially smaller than the climate model values.
2.2 Sea level rise

The IPCC AR5 projections of sea level rise are indirectly based on the CMIP5 global climate model simulations [AR5, Section 13.5.1]:

  • Thermal expansion of the ocean is derived directly from the CMIP5 climate model simulations
  • Changes in glacier and surface mass balance are calculated based the projections of the CMIP5 climate models.
  • Possible contributions from ice sheet dynamics are assessed from the published literature and are treated as independent of emissions scenario.
  • Projections of changes in land-water storage due to human intervention is assessed from the published literature and is treated as independent of emissions scenario

Table AR5 WG1 SPM.2 summarizes the sea level rise projections for 2046-2065 and 2081-2100:

The upper limit of the likely range for the extreme RCP8.5 emission scenario is 0.82 m (2.7 feet).

In all scenarios, thermal expansion is the largest contribution, accounting for about 30–55% of the projections. Glaciers are the next largest. By 2100, 15–55% of the present glacier volume is projected to be eliminated under RCP2.6, and 35–85% under RCP8.5. SMB [surface mass balance] change on the Greenland ice sheet makes a positive contribution, whereas SMB change in Antarctica gives a negative contribution. The positive contribution due to rapid dynamical changes that result in increased ice outflow from both ice sheets together has a likely range of 0.03–0.20 m in RCP8.5 and 0.03–0.19 m in the other RCPs. There is a relatively small positive contribution from human intervention in land-water storage, predominantly due to increasing extraction of groundwater.” [AR5 Section 13.5.1]

The IPCC also provides semi-empirical projections of global sea level rise that are greater than the process-model based projections. However, the IPCC concluded that:

Many semi-empirical model projections of global mean sea level rise are higher than process-based model projections (up to about twice as large), but there is no consensus in the scientific community about their reliability and there is thus low confidence in their projections”. 
[AR5 WG1, SPM p 26].

3. Possible worst-case scenarios

It is estimated that fully melting Antarctica would contribute over 60 meters of sea level rise, and Greenland would contribute more than 7 meters, with an additional 1.5 m of sea level rise from glaciers. How much of this is potentially realizable in the 21st century?

Clarifying the possible worst-case scenario for sea level rise in the 21st century is useful in context of risk management approaches. Decision makers would rarely plan for the worst-case scenario (unless you have a lot of spare money to spend on building resilience); rather you might avoid building new major infrastructure (e.g. an airport) in coastal areas that could be impacted by such a worst-case sea level rise.

With regards to the upper bound of potential 21st century sea level rise, the IPCC AR5 states:

Only the collapse of marine-based sectors of the Antarctic Ice Sheet could cause [global mean sea level] rise substantially above the likely range during the 21st century. Expert estimates of contributions from this source have a wide spread, indicating a lack of consensus on the probability for such a collapse. The potential additional contribution to GMSL rise also cannot be precisely quantified, but there is medium confidence that, if a collapse were initiated, it would not exceed several tenths of a metre during the 21st century” [AR5 WG1, Section 13.5.3].

Since the AR5, there has been increasing interest in describing the tail of the sea level rise distribution and the worst-case scenario, referred to as the H++ range. From a review by Nicholls et al. (2013):

Globally, the upper bound for this global H++ range considers the dynamic effects of the ice sheets. On the basis of an analogue of the last interglacial (about 127,000 to 110,000 years ago) when sea level, climate, and ice masses were broadly similar to today, sea levels are estimated to have risen up to 1.6 ± 0.8 m/century [16 mm/yr] with contributions coming from both the Greenland and Antarctic ice sheets. Using a different methodology, Pfeffer et al. argue that it is physically untenable for the total rise by 2100 to exceed 2.0 m and a scenario that allows for accelerated ice melt due to ice dynamics lies between 0.8 and 2.0m.

LeBars et al. (2017) provides an updated evaluation of the H++ range:

We have constructed a new high-end projection for global sea level rise in 2100 by modifying and extending the AR5 process-based method in three ways. For the RCP8.5 scenario, the PDF obtained has a median of 184 cm and a 95% quantile of 292 cm. Other so called ‘extreme’ or ‘worst’ scenarios that are not probabilistic can be compared with our PDF. The Dutch Delta Committee projects 110 cm that is between the 10% and 20% quantiles of our PDF. The UK H++ scenario of 270 cm and the NOAA scenario of 250 cm fall between the 80% and 95% quantiles of our PDF, so these values are not radically different from our high-end estimate.

Griggs et al. (2017) prepared H++ scenarios for cities along the California coast. This analysis is illuminating because it provides rates of sea level rise corresponding to the H++ values. For Crescent City, CA, Griggs et al derived an H++ value of sea level rise by 2100 to be 9.3 ft (283 cm), a value that is close to the global H++ values cited in the above paragraph. The H++ rates of sea level rise for Crescent City are 23 mm/yr for 2030-2050 and 51 mm/yr for 2080-2100. For reference, recall that the current global rate of sea level rise is about 3 mm/yr.

Are these scenarios of sea level rise by 2100 plausible? Or even possible? Let’s look at the paleo sea level record to provide context for these rates of sea level rise.

From Chapter 5 of the AR5:

Much of this sea level change occurred in 10,000 to 15,000 years, during the transition from a full glacial period to an interglacial period, at average rates of to 10 to 15 mm/yr. These high rates are sustainable only when the Earth is emerging from periods of extreme glaciation. During the transition of the last glacial maximum about 21,000 years ago to the present interglacial . . . coral reef deposits indicate that global sea level rose abruptly by 14 to 18 m in less than 500 years, in which the rate of sea level rise reached more than 40 mm/yr.” [AR5 WG1 FAQ 5.2]

Rates of sea level rise during the Holocene deglaciation are illustrated in this diagram by Donoghue et al. (2011):

What about Last Interglacial (LIG) period, ca 129-116 ka? IPCC AR5 Chapter 13 states:

For the time interval during the LIG in which GMSL was above present, there is high confidence that the maximum 1000-year average rate of GMSL rise associated with the sea level fluctuation exceeded 2 m kyr–1 but that it did not exceed 7 m kyr–1 . [2 to 7 mm/yr.] Faster rates lasting less than a millennium cannot be ruled out by these data. Therefore, there is high confidence that there were intervals when rates of GMSL rise during the LIG exceeded the 20th century rate of 1.7 [1.5 to 1.9] mm/yr. [AR5 WG1 Section]

Rohling et al. (2013) provide a geologic/paleoclimatic perspective on recent and possible future sea level rise (see new section on Rates of Sea Level Rise in Part II), using an empirical Monte Carlo style approach:

We consider a ‘worst case’ outlook from our natural perspective. The upper bound of our 95% probability envelope (i.e., the 97.5th percentile) implies a 2.5% chance of 1.8 m SLR by 2100. However, this trajectory requires that SLR rates develop toward an eventual value of 4.3 m/cy [43 mm/yr] roughly similar to mwp-1a [the onset of the last deglaciation], even though today’s global ice volume is only about a third of that at the onset of the last deglaciation. Most of the extra ice during glacial times existed in North America and northwestern Eurasia. These ice sheets were highly sensitive to climate change, as witnessed by the fact that they existed during ice ages and were almost entirely absent during interglacials. Both the size and sensitivity of these glacial ice masses would have been conducive to high deglacial rates of SLR. Starting from present-day conditions, rates such as those of mwp-1a would require unprecedented ice-loss mechanisms, such as collapse of a major ice sheet (e.g., the largely marine-based West Antarctic Ice Sheet). Alternatively, such rates might develop with a large increase in the amount of ‘vulnerable’ ice, by activation of major EAIS retreat. From the natural perspective, however, the latter only seems to become relevant under extreme GHG forcing, with long-term CO above 1000 ppmv or so. Without invoking such exceptional conditions or catastrophic events, our assessment supports the notion that 2 m of SLR by 2100 represents a useful upper limit.

How should these values of H++ be interpreted?

I am in agreement with Griggs et al. in that the H++ scenario is too uncertain to assign meaningful probabilities and that the H++ scenario should be regarded to have an unknown probability. I find the empirical approach used by Rohling et al. to be more believable than the process based approached typified by LeBars et al., given the uncertainties and known deficiencies of climate models (although I appreciate that LeBars approach avoids expert judgment).

However, even a relatively modest value of H++ = 2 m by 2100 implies unprecedented rates of sea level rise during an interglacial. This would require unprecedented ice-loss mechanisms, such as collapse of the West Antarctic Ice Sheet or activation of major East Antarctic ice sheet retreat. Rohling et al. makes the following argument for a possible very rapid ice sheet adjustment:

Anthropogenic climate forcing is more than an order of magnitude faster than climate forcing or major feedbacks at any known time since the Cenozoic [past 66 million years]. Key climate system components such as deep ocean temperature and ice volume respond slowly due to their large inertia. Ice-volume contributions to future SLR will therefore reflect delayed responses to GHG emissions, developing climate system feedbacks, and future emissions. The large and fast-growing disequilibrium between accelerated cli- mate forcing and slow/lagging response thus creates a strong potential for rapid sea-level adjustments.

JC query: Is the relatively modest anthropogenic radiative forcing since ~1750 (a few Watts per meter squared) really an order of magnitude faster than climate forcing or major feedbacks in past 66 million years? What does the ‘rate’ of forcing mean? Magnitude, or rate of change of the magnitude?

From the AR5 Chapter 5 (paleoclimate), atmospheric CO2 was higher in the Cenozoic prior to 25 mya. In terms of ‘rate of forcing’, surely major volcanic eruptions have had a greater ‘rate of forcing.’

Rohling’s justification for unprecedented SLR rates in the 21st century based on exceptional radiative forcing in the past 66 million years seems . . . unjustified. However, this appears to be a key issue in justifying a scenario of possible unprecedented sea level rise in the 21st century, it deserves further investigation.

4. Geologic wild cards

While on the subject of ‘possible’ future scenarios, we should not ignore potential geologic wild cards.

Sea level changes on Earth cannot be treated as occurring in a rigid ocean basin. Tectonics, dynamic topography, sediment compaction, prograding delta buildup, ocean floor height change sub-marine mass avalanche. and melting ice all trigger variations in the configuration of the basin and ultimately impact sea level. While some of these processes operate at very slow time scales others do not and may have substantial impact on local sea level at least. Surely such changes are as ‘possible’ as a collapse of the West Antarctic ice sheet in the 21st century.

In the more ‘likely’ category of geologic impacts is geothermal heat flux in the vicinity of the Greenland and Antarctic ice sheets. Here are some recent papers that I have spotted:

High geothermal heat flux in proximity to the Northern Greenland ice stream
The Greenland ice sheet (GIS) is losing mass at an increasing rate due to surface melt and flow acceleration in outlet glaciers. A compilation of heat flux recordings from Greenland show the existence of geothermal heat sources beneath GIS and could explain high glacial ice speed areas such as the Northeast Greenland ice stream.

A new volcanic province: an inventory of subglacial volcanoes in West Antarctic.
We identified 138 volcanoes, 91 of which have not previously been identified, and which are widely distributed throughout the deep basins of West Antarctica, but are especially concentrated and orientated along the >3000 km central axis of the West Antarctic Rift System.

Influence of a West Antarctic mantle plume on ice sheet basal conditions
“The experiments show that mantle plumes have an important local impact on the ice sheet, with basal melting rates reaching several centimeters per year directly above the hotspot.”

Heat Flux Distribution of Antarctica Unveiled
Of the basic parameters that shape and control ice flow, the most poorly known is geothermal heat flux. We present a high-resolution heat flux map and associated uncertainty derived from spectral analysis of the most advanced continental compilation of airborne magnetic data.

Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet. “large areas at the base of Thwaites Glacier are actively melting in response to geothermal flux consistent with rift-associated magma migration and volcanism. This supports the hypothesis that heterogeneous geothermal flux and local magmatic processes could be critical factors in determining the future behavior of the West Antarctic Ice Sheet.”

The first physical evidence of subglacial volcanism under the West Antarctic Ice Sheet. “New evidence from ice core tephra shows that subglacial volcanism can breach the surface of the ice sheet and may pose a great threat to WAIS stability.”

Melting at the base of Greenland ice sheet explained by Iceland hotspot history. “large parts of the north-central Greenland ice sheet are melting from below. It has been argued that basal ice melt is due to the anomalously high geothermal flux1,4 that has also influenced the development of the longest ice stream in Greenland

JC query: any additional recent papers? I would be most interested to know if any of this is being factored in to the attribution of ice sheet contribution recent sea level rise.

5. Recent projections of global sea level rise

Since the IPCC AR5 was published in 2013, new scenario and probabilistic approaches have been used for 21st century sea level rise projections.

In 2017, the U.S. National Oceanic and Atmospheric Administration (NOAA) published a Technical Report entitled Global and Regional Sea Level Rise Scenarios for the United States.

In order to bound the set of GMSL rise scenarios for year 2100, we assessed the most up-to-date scientific literature on scientifically supported upper-end GMSL projections, including recent observational and modeling literature related to the potential for rapid ice melt in Greenland and Antarctica. We recommend a revised ‘extreme’ upper-bound scenario for GMSL rise of 2.5 m by the year 2100. [We] revise Parris et al. (2012)’s estimate of the lower bound upward by 0.1 m to 0.3 m by the year 2100.” [NOAA, 2017, p. vi]

Figure 8 from the NOAA Report illustrates the evolution of the six global mean sea level rise scenarios over the 21st century:

Table 4 from the NOAA (2017) Report provides probabilities of the global mean sea level (GMSL) exceeding each sea level rise scenario for each of three emissions scenarios. The closest emissions scenario for the path that global emissions appear to be following is between RCP4.5 and RCP2.6.Scenarios exceeding 1.5 m (4.9 feet) of sea level rise in the 21st century have a probability of less than 1% for RCP4.5.

The California Ocean Protection Council has published a new report (April, 2017) entitled Rising Seas in California by Griggs et al. This report has taken a slightly different approach than NOAA (2017):

  • Offers probabilistic sea level rise projections.
  • The maximum physically plausible extreme scenario is regarded to have an unknown probability.

The report provides the following probabilistic projections for San Francisco:

Table 1. Projected sea-level rise (measured in feet) Projections are based on the methodology of Kopp et al., 2014 with the exception of the H++ scenario. The ‘likely range’ is consistent with the terms used by the IPCC meaning that it has about a 2-in-3 chance of containing the correct value. All values are with respect to a 1991- 2009 baseline. The H++ scenario is a single scenario, not a probabilistic projection, and does not have an associated distribution in the same sense as the other projections; it is presented in the same column for ease of comparison.

Table 2 shows the rates of sea level rise associated with the above values of sea level rise.

Table 2. Projected average rates (mm/year) of sea-level rise Projections are based on the methodology of Kopp et al., 2014 with the exception of the H++ scenario. For example, there is a 50% probability that sea-level rise rates in San Francisco between 2030-2050 will be at least 3.8 mm/year. The ‘likely-range’ is consistent with the terms used by the IPCC meaning that it has about a 2-in-3 chance of containing the correct value. The H++ scenario is a single scenario, not a probabilistic projection, and does not have an associated distribution in the same sense as the other projections; it is presented in the same column for ease of comparison.

The categories (columns) used in the above tables are very useful for decision making:

  • The first column (median) is useful for ‘more likely than not’ assessments of relevance for civil lawsuits, whereby SLR values lower than the median would arguably correspond to ‘more likely than not values.’
  • The second column (likely) hews to the IPCC’s apparent rationale for supporting the UNFCCC CO2 emission policies by providing a range that is sufficient to trigger the precautionary principle.
  •  The fourth column (1-in-200 chance) corresponds to the level of financial risk taking in risk-based capital assessments used in the insurance industry.

The issue with these projections is whether they are credible, based upon our background understanding the myriad and complex processes that determine sea level change and the limitations of climate models. Not to mention concerns about whether the climate model ensemble of opportunity provides an appropriate basis for probabilities.

6.  Critical assessment of sea level rise projections

Process-based sea level rise projections for the 21st century are becoming more sophisticated and no longer rely on expert judgment. However, these projections are only as valid as the climate model simulations upon which they are based.

Apart from the uncertainties in the climate models described at the beginning of this essay, there are two overarching problems with these projections:

  • The scenarios of future climate are incomplete, focusing only on emissions scenarios
  • The opportunistic ensemble of climate model simulations (CMIP5) do not provide the basis for the determination of statistically meaningful probabilities.

Both the IPCC AR5 and the NOAA Report acknowledge the constraints, assumptions, contingencies and uncertainties of their projections of sea level rise.

The climate model projections of 21st century surface temperature and sea level rise are contingent on the following assumptions [AR5 WG1]:

  1. Emissions follow the specified concentration pathways (RCP). Tone down these scenarios; RCP8.5 is completely unrealistic, we appear to on a trajectory somewhere between RCP4.5 and RCP2.6 [12.2.3]
  2. Climate models accurately predict amount of warming in 21st century. There is evidence that climate models are too sensitive to CO2 and produce too much warming. [Box 12.2]
  3. The projections assume that solar variability follows that of the late 20th century, which coincided with a Grand Solar Maximum. [AR5, Section] Some Russian and German scientists are predicting a Grand Solar Minimum in the mid 21st century.
  4. The projections assume that natural internal variability of ocean circulations doesn’t impact temperature or sea level rise on these timescales. [Section 12.2.3, 3.6]
  5. The projections ignore volcanic activity, which overall has a cooling effect on the climate. IPCC quote[Section 12.2.3, 8.4.2]

Each of these contingent assumptions, with the possible exception of natural internal variability, most likely contribute to a warm bias in the 21st century projections.

Rather than focusing on sensitivity to emissions scenarios, just focus on RCP2.6 and RCP4.6. Additional scenarios that should be considered for the 21st century (individually or in combination):

  • Scenario of volcanic eruptions matching the 19th century eruptions
  • Grand solar minimum in the mid 21st century
  • Transition to the cold phase of the Atlantic Multidecadal Oscillation
  • Transient sensitivity to CO2 of 1.3C (or a range from 1.0 to 1.9C)

Apart from volcanic eruptions, climate models don’t handle these very well (notably the solar indirect effects and phasing and cloud feedbacks associated with the AMO); hence semi-empirical approaches would be needed in generating these scenarios. While some back of the envelope scaling factors can be estimated for these, if anyone were to take on development of these alternative scenarios, it would be a nontrivial effort.

So, what are we left with in estimating the sea level rise mid 21st century and at the end of the century? The best options seem to me:

  • Extrapolate the current trend of 3 mm/yr to mid century. The current rate has a bump from Greenland melting that is coincident with and likely associated with the warm phase of the AMO (see Part V). A transition to the cool phase of the AMO may occur sometime within the next few decades, which would slow the mass loss from Greenland, which would be supplemented by perhaps more rapid thermosteric component, maintaining the current rate of sea level rise to mid century.
  • Use the RCP2.6 values from the IPCC/NOAA/California assessments. Even if we are not quite on the RCP2.6 path for emissions, this could be countered by lower sensitivity to CO2, so there are two paths to the sea level rise predicted by the RCP2.6 scenario.
  • The other sea level rise scenarios presented by IPCC/NOAA/California are possible (whether their H++ scenarios above 2m are possible is debatable), but probabilities cannot be meaningfully provided for these scenarios.


The bottom line is that the sea level rise will continue to rise in the 21st century, probably at a rate more than 8 inches observed in the 2oth century. And there will be substantial regional and local variations in the rate of sea level rise. Reducing emissions will have little effect on sea level rise in the 21st century even if you believe the climate models; compare the difference in sea level rise for the RCP2.6 versus RCP4.5 scenarios.


And what about the wildcard events, such as collapse of the West Antarctic Ice Sheet or some major geological event? They are wildcards; the West Antarctic Ice Sheet is much more likely to collapse in the 21st century from a geological event than it is from greenhouse gas emissions.

The NOAA Report sums it up this way:

As is discussed in detail in this report, scientists expect that GMSL will continue to rise throughout the 21st century and beyond, because of global warming that has already occurred and warming that is yet to occur due to the still-uncertain level of future emissions. GMSL rise is a certain impact of climate change; the questions are when, and how much, rather than if. There is also a long-term commitment (persistent trend); even if society sharply reduces emissions in the coming decades, sea level will most likely continue to rise for centuries.

We need to figure out ways to systematically adapt to systematic sea level rise.

333 responses to “Sea level rise acceleration (or not): Part VI. Projections for the 21st century

  1. If I project 3 mm/yr to 2050 I get about 3.8 inches (9.6 cm).
    It will be interesting to see how this compares to what we eventually see by 2050.
    It doesn’t seem like a very big problem to me, especially given 120 meters of rise over the last 20,000 years.

  2. Pingback: Sea level rise acceleration (or not): Projections for the 21st century — Climate Etc. – NZ Conservative Coalition

  3. It is seen that the large El Nino of 2016 has returned the observed temperature curve to near the middle of the envelope of climate model simulations; however the previous large El Nino of 1998 was at the top of the envelope of climate model simulations. The recent data since 2012 continues to indicate that the sensitivity of at least some of the climate models to CO2 forcing is too high. … – from the article

    The data since 2012 indicates an upward trend of .065 ℃ per year.

    To date, the subsequent years after a prior El Niño record temperature event have seen the record El Niño temperature shattered, which means those were not El Niño caused record GMSTs, they were likely 100% caused by ACO2.

    Why would it be different for the 2016 El Niño?

  4. A recent study is Why would sea-level rise for global warming and polar ice-melt? By Aftab Alam Khan published in Geoscience Frontiers.

    This study is based on the geophysical aspects of the earth wherein shape of the earth is the fundamental component of global sea level distribution. The physical surface of the earth adjusted to the mathematical surface of the earth is spheroidal. This spheroidal surface always coincides with the global mean sea level (Fig. 3). Having relationship between the shape of the earth and the global sea level, gravitational attraction of the earth plays a dominant role against sea level rise. Gravity is a force that causes earth to form the shape of a sphere by pulling the mass of the earth close to the center of gravity i.e., each mass-particle is attracted perpendicular towards the center of gravity of the earth (Fig. 4A).

    A geoid surface thus prepared exhibits bulges and hollows of the order of hundreds of kilometers in diameter and up to hundred meter in elevation occurring in the zone mostly between 60°N and 60°S latitudes. Marked changes in the contour pattern of the geoid height in the zone between 60°N and 60°S suggests maximum curvature along 60°N and 60°S. Hence any change of the global sea level due to the predicted ice melt would not extend beyond 60°N and 60°S. However the reality is that no sea-level rise actually would occur due to ice melt as a result of same volumetric replacement between melt-water and floating ice.


    Geophysical shape of the earth is the fundamental component of the global sea level distribution. Global warming and ice-melt, although a reality, would not contribute to sea-level rise. Gravitational attraction of the earth plays a dominant role against sea level rise. As a result of low gravity attraction in the region of equatorial bulge and high gravity attraction in the region of polar flattening, melt-water would not move from polar region to equatorial region. Further, melt-water of the floating ice-sheets will reoccupy same volume of the displaced water by floating ice-sheets causing no sea-level rise. Arctic Ocean in the north is surrounded by the land mass thus can restrict the movement of the floating ice, while, Antarctic in the south is surrounded by open ocean thus floating ice can freely move to the north. Melting of huge volume of floating sea-ice around Antarctica not only can reoccupy volume of the displaced water but also can cool ocean-water in the region of equatorial bulge thus can prevent thermal expansion of the ocean water. Melting of land ice in both the polar region can substantially reduce load on the crust allowing crust to rebound elastically for isostatic balancing through uplift causing sea level to drop relatively. Palaeo-sea level rise and fall in macro-scale are related to marine transgression and regression in addition to other geologic events like converging and diverging plate tectonics, orogenic uplift of the collision margin, basin subsidence of the extensional crust, volcanic activities in the oceanic region, prograding delta buildup, ocean floor height change and sub-marine mass avalanche.

    Synopsis with images and links at≠-sea-level-rise/

  5. The Greenland glacier did not form until after the CO2 levels dropped below 400 ppm over 12 million years ago. It has not existed at these levels before and so any CO2 increase pushes us further past that tipping point. Its melt rate will only increase as CO2 levels rise, and it already contributes 25% of the sea-level rise rate having contributed almost nothing to the rate prior to 2000. This is a fast accelerating component of SLR. Even if these melt rates continue to only double every ten years, we get several meters by 2100.

    • Without relevant citations there is no credibility.

      • You need to find something to refute it first because I am not going to try and guess what you don’t agree with. Is this all new to you? It shouldn’t be.

      • What I do or don’t agree with is irrelevant. If you are going to make claims with any credibility you need to cite science. Without citations it is impossible to assess the accuracy of claims such as yours above.

      • Say what part is new to you.

      • Support your claims with citations. Is that too much to ask? Seems so.

      • Didn’t we have this same go around a couple of weeks ago?

      • Rob,

        Jim D doesn’t have to provide citations.

        He was there.

        At least in spirit.

        Or maybe just in his mind.

        Besides, why start now with credibility when he’s gone so long without it?

    • Asking for citations?

    • “melt rate will only increase as CO2 levels rise”

      Your premise that increased temperature will decrease snow on Greenland is contradicted by the positive correlation of ice accumulation with temperature from the GISP data:

      To be sure, that’s at the summit and not total Greenland mass, which is only constrained by estimates of the last few decades. But most of Greenland has an elevation of greater than 2 kilometers. And many melt days have always taken place at the periphery which is closer to sea level:

      • Greenland is net losing mass and contributing 0.75 mm/yr to sea-level rise currently. This is not surprising given the CO2 levels relative to what Greenland has experienced before.

      • “Greenland is net losing mass and contributing 0.75 mm/yr to sea-level rise currently.”

        (rhetorical) Is that unusual for the last 10,000 years?

        Perhaps not.

        If accumulation is almost always occurring at high elevation, and melting is almost always occurring near sea level, it would appear that perfect stasis was not a frequent occurrence.

      • As I said, I am not surprised because we are at 400 ppm and climbing and this climate we have entered does not support Greenland’s ice. If recent paleoclimate tells us anything, it tells us these glaciers are fragile, and they have tipping points.

      • “On 103- to 106-year timescales, global sea level is determined largely by the volume of ice stored on land, which in turn largely reflects the thermal state of the Earth system.”

        The first line in the reference Jimmy’s graph comes from. How can they go on to ignore ice albedo? CO2 is largely a biokinetic feedback and does not initiate ice sheet changes.

        Then we have to make fossil fuels too expensive to use to save them for poor people. It is the whole calamity with Jimmy.

    • I only ask because the Greenland ice sheet didn’t appear until some 3 million years ago. That’s considerably later than 12 million years ago. A glacially slow tipping point?

      • That might be the continuous glaciers. It had ice before that.

      • …because you don’t believe it when paleoclimate tells us that high CO2 levels prohibit continental glaciers?

      • You haven’t presented any evidence. I won’t say what I believe about that.

      • It’s just as easy for you as me to find how CO2 values of over 400 ppm have not coincided with Greenland’s ice periods whether you want it to be 5 million or 15 million years. This is typical of many.
        Also slides 75-76 of that presentation.

      • You made the claim Jimmy boy – so talk the talk or walk the walk.

      • Given the higher CO2 levels in most of the Miocene, Wikipedia may have been wrong, but there have been sporadic studies on early Miocene ice, so maybe Wikipedia got it from there.

      • “Recent studies show that there was no significant topography in East Greenland at 10 Ma and that much of the uplift has occurred since ~5 Ma (Bonow et al., 2014; Japsen et al., 2014). Glacial erosion can cause uplift of the remaining mountains, but this mechanism cannot explain the overall high topography (Medvedev et al., 2013). Significant parts of Greenland’s uplift appear to pre-date large-scale glaciations, but not by more than several millions of years, so that a causal link appears viable (Japsen et al., 2014). Here we suggest how three geodynamic processes were fundamental in preconditioning the extensive ice-sheet buildup during the Pliocene: the Iceland plume affecting uplift in East Greenland, the plate tectonic movement of Greenland since ~60 Ma and a rotation of the Earth’s crust and mantle, called true polar wander (TPW).”

        Greenland in the Miocene is not a modern climate analogue. That’s evidence for you Jimmy.

      • At about 380 ppm, the Miocene would have been marginal for Greenland ice, but as we crossed 380 ppm shortly after 2000, Greenland mass started to take a dive, so it makes sense in the big picture.

      • That’s your evidence?

      • Jim D wrote, “paleoclimate tells us that high CO2 levels prohibit continental glaciers.”

        “Paleoclimate” tells us no such thing. It tells us that Greenland was probably ice-free in the early Miocene, and that CO2 levels were high. That certainly doesn’t mean high CO2 levels caused Greenland to be ice-free.

        Antarctica averages well below -40°, and ice mass gains and losses are in near perfect balance there. A few degrees of warming can’t possibly melt that ice. (In fact, by increasing snowfall, warming might increase ice accumulation on the ice sheets.)

        Most of the Greenland Ice Sheet is also too cold to be melted by a few degrees of warming. The southern part is is currently losing ice, but at a glacially slow rate. At the current rate it would take 90 to 150 centuries to lose it all.

        Compare that to an anthropogenic CO2 pulse which will last only a few centuries, and it is obvious that melting of such magnitude, from the moderate warming caused by that brief CO2 rise, is not plausible.

        Additionally, we know that nine centuries ago, during the MWP, it was warm enough in southern Greenland that the Vikings were able to grow barley there, and it is too cold to grow barley there now, even with modern, quick-maturing cultivars. Yet that relatively warm Greenland did not contribute enough meltwater to the world’s oceans to be notable elsewhere in the world.

        What’s more, we have some experience with the effect of temperature changes on sea-level. The approximately 1°C of warming which the Earth has experienced since “pre-industrial” (Little Ice Age) conditions was associated with only a very, very slight acceleration in sea-level rise, all of it at least ninety years ago.

      • So far you haven’t been able to dispute that Greenland has no ice above 400 ppm, and only confirmed that the limit for large glaciers may be even lower. What else do you need? Case closed.

      • CO2 has been below 400 – in ice cores – for the entire existence of northern ice sheets. We may be about to do the experiment – but geodynamic processes as described elsewhere caused the glaciation only a couple of million years ago.

      • You have to realize that there is a difference between Greenland and the northern continental ice sheets that only existed in the Ice Ages of the last 2 million years. Greenland precedes those by millions of years and lasted through all the interglacials. It has been more robust, until now when it sees 400 ppm for the first time in its existence.

      • The Greenland ice sheet began to build around 2.6 million years ago, About the start of the Pleistocene. The most recent of the ice ages that continues to this day. Geodynamic factors – uplift, tectonic plate movment northward and a wandering true north has more to do with its formation and stability than CO2..

      • You’ll find other references that say 5-8 million years ago. What was the CO2 level 3 million years ago before Greenland could exist according to you? This is why its formation date is of interest for this discussion.

      • Yes Jimmy – show me the science. CO2 is a biokinetic and ocean solubility response to temperature largely – and a little venting. It was getting cooler – less CO2 – but perhaps it was uplift or Greenland wandering a bit far north. Perhaps it was the shoaling of the Isthmus of Panama and Gulf Stream and heat transport changes. There are never easy answers even today – and paleo data is enormously uncertain. But the Greenland ice sheet seems relatively recent – and you have not a skerrick of any scientific support for your claims. Waffling about snow drifts in the Miocene with unreferenced Wikipedia claims for scientific support is not quite the same thing.

      • I think when the skeptics realize that 400 ppm is way above what can support Greenland’s ice sheet they will see CO2 and its link to sea level more realistically. They’re not there yet, but they see the evidence. Anyway, until then, denial, blinking disbelief, a lot of headscratching, and a lack of understanding of what’s already happening. It’s interesting to see.

      • Dave Burton, the Greenland glacier did exist nine centuries ago. They did not exist in much if any of the Miocene when CO2 levels were nearer 400 ppm. Similarly Antarctica did not freeze until CO2 levels dropped somewhat below 700 ppm. There is a strong and unsurprising relation between sea levels and CO2 levels in the last 50 million years.
        Also the new melt rate has already accelerated the sea level rise rate by 1 mm/yr since 2000 with more to come.

      • “On 103- to 106-year timescales, global sea level is determined largely by the volume of ice stored on land, which in turn largely reflects the thermal state of the Earth system.”

        The first sentence of the reference Jimmy’s graph comes. How can they start like that and ignore albedo? Odd indeed.

        Then Jimmy wants to make fossil fuels so expensive they can’t be used to save them for poor people. With Jimmy it is the whole calamity.

      • If you look at graphs over long periods, glacial melt is what causes changes of order meters. Nothing else does that much. Albedo from ice cover is a big positive feedback factor, but that’s a given for anyone how knows how the Milankovitch mechanism works.

      • You’ve just rediscovered Milankovitch. Progress, I guess. Maybe now if you can link in your knowledge of sea levels, you will get the picture. It’s the glaciers. Their presence or absence depends on factors including Milankovitch and general CO2 levels. The Ice Ages didn’t start until CO2 levels dropped to somewhere around 300 ppm. That was the first necessary ingredient. The Milankovitch mechanism doesn’t work with high CO2 levels for obvious reasons related to the extent of annual cycle of Arctic ice cover.

      • There is a paradox of the heart of that study that is over your head Jimmy.

      • OK, so you’re not going with the Milankovitch albedo effect? What’s your new belief?

      • I’m going with science – and the study linked is well done and consistent with current thinking. Why – what are you going with?

      • It seems OK, but you’re not going to explain sea level without glaciers using that. It was a diversion tactic, and I can see through it. Why did the Ice Ages start when they did? Does it answer that one? You need to divert better.

      • You make claims without any scientific support and expect me to take you seriously?

      • Not sure I need to explain ice and sea level to anyone but a 10 year old.

        There are a number of factors in the inception of glacials and intergalacials – but Jimmy has a one track mind that has gone off the rails. I am not going with him.
        There are questions that have no answers – and if he has no actual science to show for it then it is all just climate catastrophe word salad.

      • One question you can’t seem to even ask is why northern ice did not exist last time we were at 400 ppm, and what that portends for it now that we have returned to those levels. If we learned anything from the last few million years it is that glaciers are fragile and tipping points abound with them. Greenland’s mass is going over the edge at this CO2 level and you will deny it all the way down, just like you are denying the warming continuation all the way up.

      • No actual science yet? Get back to me.

      • Thanks for the laugh but I don’t do climate blogs – certainly not that one.

      • Of course not, and you won’t believe sea levels in the Oligocene-Eocene-early Miocene either when CO2 levels were last above 400 ppm. It’s a problem you have, and I can’t make you research that for yourself.

      • Show me the science.

      • I do show you and you don’t believe it. Your next step is to find it for yourself. Google is your friend.

      • Science is what is published in peer reviewed journals. I don’t think you understand that.

      • That’s why they have links to papers on SkS.

      • Well try copying them and making an actual point.

      • I showed the graphic of CO2 and sea level already. Do you want to see it again? You had no answer last time either.

      • I even found the study at the PNAS. The ebb and flow of ice sheets creates an internal feedback that changes albedo. Carbon dioxide levels are a biokinetic and chemical feedback. There are multiple factors.

        “The answer to this conundrum can be found in a novel reanalysis of the effects of decreasing atmospheric CO2 concentrations during an ice-age. Ice age CO2 reductions coincide with an increase in ice sheet extent and therefore an increase in global albedo, and this should result in further cooling of the climate. But what actually happens is that when CO2 reaches a minimum and albedo reaches a maximum, the world rapidly warms into an interglacial. A similar effect can be seen at the peak of an interglacial, where high CO2 and low albedo results in cooling. This counterintuitive response of the climate system also remains unexplained, and so a hitherto unaccounted for agent must exist that is strong enough to counter and reverse the classical feedback mechanisms.”

        There is a paradox at the heart of these cyclic transitions – but you have no doubt, no science and no poetry.

      • Diverting to how CO2 and H2O feedbacks help amplify dust effects in the Ice Ages is nothing to do with what happened before them. Even higher CO2 levels existed prior to the Ice Ages, and you seem not to know why those are connected.

      • As I said originally – conditions prior to the Quaternary are not an analogue for modern climate – quite obviously. Greenland moved north and uplifted. Ice on the Nordic seas varies with flow over the Greenland-Scotland ridge on 1500 year (+/- 500 years) cycles. Heat transport north varies with freshening and in the Atlantic bottom water formation zones The Antarctic has been frozen for 34 million years. At the estimated rate of Greenland mass loss it would take 12,000 years to melt. But you take the fun out of science.

      • Greenland is melting because 400 ppm does not support a glacier at that latitude, and with a doubling time of 10 years, it could contribute meters by 2100. It is past a tipping point, and that can mean exponential growth rates. There have been such rates per century before under weaker forcing changes.

      • Greenland would have moved about 50 km in the couple of million years it took its ice sheet to form. Whose theory is that which says continental drift caused it? Yours?

      • It is actually 6 degrees of latitude from tectonic plate movement – and 12 degrees from true north wander. So that’s a whopping 2000 kilometers closer to the pole?

        I have read the original source. See that’s how it is done.

      • Now it is even closer to the pole and melting. What happened? There’s clearly an important factor you are ignoring. Anyway at 25 km per million years, it would take 24 million years to move 6 degrees and 6 degrees is only a quarter of its extent. How does the whole thing freeze when it moves a small fraction of its extent? It’s the declining CO2 and its H2O feedback because Greenland wasn’t the only place that was cooling at that time.

      • There are also substantial increases in elevation. And what you are assuming a constant velocity and ignoring true north wander?

        The melting is thus far minor – 12,000 years to melt the lot – and may be cyclical. Even in the unlikely event that we don’t lose the natural warming you ignore so assifously – the anthropogenic CO2 will spike be over well before it becomes a problem.

        Get back to me in about a 1000 years.

      • It’s the warmest it has been and the farthest north at the same time. Bang goes your theory that you are clearly just making up as you go along. Not just Greenland, the whole Arctic area is warming, and you claim not to have even a clue why the most noticeable warming in the last century has happened there and now.

      • That temperature graph is the Arctic circle. It seems as warm in the 1940’s as now.

        “The anthropogenic component of the Arctic warming was estimated by subtracting the natural variability (solar variability, volcanic eruptions, ENSO, and AMO) from the observed Arctic temperature [Foster and Rahmstorf, 2011; Zhou and Tung, 2013]. We find the recent (1985–2012) rate of anthropogenic Arctic warming to be 0.31 K ± 0.02 K per decade. Since the Arctic has warmed in recent decades at the rate of about 0.64 K/decade, our results suggest that about half of the observed recent Arctic warming trend could be attributed to anthropogenic causes.”

        You talk and talk and are incapable of presenting any evidence for your assertions. You are utterly hopeless.

      • Have you now decided that GHGs are a big factor in Arctic warming after all? Even at only half they get 0.3 K per decade, which is as much as the global land warms. They don’t attribute as much to Arctic amplification as others do, but that is just because this is a curve-fitting exercise that is not using physically based coefficients.

      • Most of the early 20th century and half the late century warming will be lost this century. And the curve at least fits – unlike your temperature and CO2. It is in fact a ‘structural analysis’. “Although structural analysis cannot prove causation, it can suggest the most plausible set of factors that influence the observed variable. We apply structural model analysis to the annual mean Arctic surface air temperature from 1900 to 2012 to find the most effective set of predictors and to isolate the anthropogenic component of the recent Arctic warming by subtracting the effects of natural forcing and variability from the observed temperature. We find that anthropogenic greenhouse gases and aerosols radiative forcing and the Atlantic Multidecadal Oscillation internal mode dominate Arctic temperature variability. ” No mystery there.

      • This is your hope that the AMO is really a cycle and not just a data artifact that owes its last upswing to the accelerating GHG effect as correctly detrended AMOs would account for. If it is not detrended correctly it takes away from the GHG effect in their analysis.

      • Eh – the AMO is a secondary effect from changes in circulation induced by changes in the Northern Annular Mode – that with actual solar decline this century will cool northern reaches by a few degrees.

        The Pacific – not the {PDO) is the source of warming and cooling – however – with cloud changes anti-correlated with sea surface temperature dominating global cloud change (Clement et al 2009). Warming cloud feedbacks are piddling – 1W/(m2.K) at best (AR5 s7).

        Did Michael Mann just notice this?

        Nor is ‘springback’ all that likely I’m afraid. The 20th century saw a 1000 year peak in warm Pacific conditions.

        What caused this?

      • They did not include the Pacific. Why not? If they want the AMO, they have to separate it from the GHG signal first, otherwise they fool themselves and a few hapless readers. They had the GHG signal. Why not use it to help detrending anything else with a temperature dependence? Mann shows how. The first rule of these kinds of fits is to have independent factors to start with, not conflated ones.

      • Who didn’t include the Pacific? This is weirdness squared.

      • ENSO is not a long-term trend and won’t contribute, no PDO, PMO or long-term thingummy like AMO. Why not? How do they decide what to include or not?

      • Who is they? You’ve lost me – but the discussion passed the point of being worthwhile long ago anyway. It is just incomprehensible word salad by now.

      • Your Arctic curve-fitters. They had no long-term Pacific curve in their fitting parameter set, and you were saying the Pacific should be a bigger factor than AMO because of all the positive cloud feedback going on there. The ENSO index doesn’t count because it is dominated by short-term fluctuations.

      • “The set of explanatory variables used included radiative forcing by anthropogenic greenhouse gases (GHG), anthropogenic aerosols (AER), solar variability (SOL), volcanic aerosols (VOLC), and oceanic influences characterized by the El Niño–Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO). ”

        It is rather pointless because you don’t read any of the references. But what they found was that the AMO co-varied with Arctic temperature.

        It is the same reality that you assiduously ignore.

      • It also co-varied with global temperatures. Even the southern oceans alone.
        That could have been a big factor if they included it.

      • I have accidentally discovered how to start Youtube videos at any point. You will need to slide the control to the left to start at the beginning.

      • The question is posed without a shred of scientific evidence for any of it.

      • A question is not evidence. A question is a question, and you can divert from it if you want too.

      • Your question presumes things that are not in evidence. Mind you – I am still looking for actual scientific evidence. But if you want to say something – provide the evidence.

      • You confine your reading to Tsonis modeling papers, so you need to expand your reading a bit.

      • I link to and quote hundreds of scientists. You just refuse to read it.

      • Quote someone on sea levels in the early Miocene then when CO2 was at 400 ppm. That would be on topic and not a diversionary tactic like all this is.

      • That’s your assertion – prove it.

      • There was even a picture, several times now. What’s the point?

      • Actual and relevant science. And hopefully more than one reference.

      • That’s fine, you won’t believe sea levels were 20 m higher 20 million years ago, and that’s that. Nothing will convince you. Here’s another one for you to deny.

      • Jim D wrote, “So far you haven’t been able to dispute that Greenland has no ice above 400 ppm… What else do you need? Case closed.”

        Beware of spurious correlations. Greenland also had no cell phones when CO2 was at 500 ppmv. That doesn’t mean that 500 ppmv CO2 level is incompatible with cell phones.

        At the current rate of net ice loss, it would take 90 to 150 centuries for Greenland to lose its entire ice sheet. Compare that to an anthropogenic CO2 pulse which will last only a few centuries.

        Already, with CO2 at only 407 ppmv, biological and chemical “negative feedbacks” are removing about 16 Gt of CO2 each year — the equivalent of about 2.5 ppmv — and the higher levels go, the faster those mechanisms remove CO2 from the atmosphere. How long do you think CO2 levels can remain this high?

        Here are a couple of relevant papers:

      • Technology will change faster than fuel depletes.

      • Dave Burton, yes, you’re making the old “fossil fuels won’t even last till 2100” argument. All the more reason to get off them before those prices skyrocket through demand, if that is the case, right? To save any past 2100, for poor countries for example, requires large reductions in emission rates before 2100. Same goal, different reason.

      • Don Monfort

        When it becomes evident that fossil fuels are actually running out, rather than being projected to run out, they will be replaced by nuclear power. End of story.

      • Jim D wrote, “Greenland is melting because 400 ppm does not support a glacier at that latitude, and with a doubling time of 10 years, it could contribute meters by 2100. It is past a tipping point, and that can mean exponential growth rates.”

        That’s ridiculous, Jim. CO2 levels have been rising dramatically for 2/3 century, and if that were causing dramatic acceleration in Greenland ice mass loss it would be evident in sea-level measurements at places like Honolulu — which obviously hasn’t happened. What’s more, I just showed you that during the MWP Greenland was warmer than present, without contributing enough meltwater to the world’s oceans to be notable elsewhere in the world.

        Anytime a climate alarmist starts going on about “tipping points” and “exponential growth rates” it means they’ve abandoned science, and cannot be taken seriously.

        Jim D wrote, “Greenland would have moved about 50 km in the couple of million years it took its ice sheet to form.” But Robert replied, “It is actually 6 degrees of latitude from tectonic plate movement – and 12 degrees from true north wander. So that’s a whopping 2000 kilometers…” and he cited this (very interesting!) article.

        But y’all aren’t as far apart as you think, because Jim’s talking about 2 million years and Robert’s talking about 60 million years.

        This source says the plates move 1 to 10 cm/year:

        Call it 5 cm/yr = 0.05 m/yr.

        (2,000,000 yr) × (0.05 m/yr) / (1000 m/km) = 100 km

        which is not far from Jim’s 50 km figure.

        Additionally, “true north” apparently currently drifts at an average rate of about 10 cm/year. So that could add another 200 km shift in 2 million years. (But it’s the mass shifts which trigger such movement, so more rapid mass changes [e.g., during glaciation / deglaciation cycles] could presumably cause more rapid drift of True North, right?)

        So the large change in Greenland’s distance from the north pole, that Robert mentioned, is presumably at least one of the reasons Greenland didn’t get an ice sheet until about 3 million years ago, and the few hundred km by which Greenland may have moved north since then just helps lock in the glaciation.

        However, IMO makes no sense to try to attribute Greenland’s ice sheet to just one factor, like CO2 level or continental drift. The truth is that we are clueless about many important variables which could have been very, very different that long ago.

        We don’t even know what caused the Roman Climate Optimum, the Dark Ages Cold Period, the Medieval Warm Period, The Little Ice Age, or the recovery from the LIA — all within the last 2300 years. Two million years is 870× that long.

        People’s minds aren’t good at groking extremely long periods of time. How about this: two million years is 8,264 times as long as the USA has existed as an independent country. Do you think we have any idea what the Sun has done, over that time span?

        We have good evidence that TSI doesn’t change much over periods of a few decades, even as solar cycles wane and wax in strength.

        Does that mean it doesn’t change over periods of a few centuries? Perhaps. But the evidence is certainly weaker.

        How about a few millenia? We really don’t have any way of knowing.

        How about a few tens of millenia? Seriously?? We have absolutely no clue!

        How about a few hundreds of millenia? Ditto, but 10× more so.

        How about thousands of millenia? You’ve got to be joking!

      • Jim D wrote, “It’s the warmest it has been and the farthest north at the same time.”

        Assuming you’re still talking about Greenland, did you miss the part about the Norse settlers there nine centuries ago growing barley — even though the growing season there is now too short to grow barley? Greenland has warmed a bit (and that’s a good thing!), but not enough to fully recover from LIA cooling.

        Greenland ice mass loss has been going on for a long time, almost certainly since recovery from the LIA began. Although direct measurements via satellite from which ice mass balance can be deduced don’t go back very far, we can tell from sea-level trends that Greenland ice mass loss cannot have appreciably accelerated in response to elevated CO2 levels over the last 2/3 century. If it had, then it would have caused sea-level rise at distant locations to accelerate significantly, and that hasn’t happened.

        Here’s a very high quality continuous 112-year mid-Pacific sea-level measurement record from a tectonically stable location, little affected by ENSO sloshes, juxtaposed with CO2. The CO2 trace obviously accelerated quite a bit in the 1950s and 1960s, but if anyone thinks he sees significant acceleration in the sea-level trace, he needs to get his eyes (or head) checked:

    • jimeichstedt

      What was the earth’s temp when carbon dioxide levels were last 400ppm? Earth’s temperature has been declining for 55 million years…

      • It was warmer than the Ice Ages which is why we didn’t have them back then. Now we are in a phase that permits Ice Ages, at least until recently when CO2 levels make Greenland melt again. I think Greenland is a tipping point for the skeptics, so they are paying close attention to its trend. As it melts away, so does their skepticism.

  6. JC query: any additional recent papers? I would be most interested to know if any of this is being factored in to the attribution of ice sheet contribution recent sea level rise.

    The first physical evidence of subglacial volcanism under the West Antarctic Ice Sheet


    The West Antarctic ice sheet (WAIS) is highly vulnerable to collapsing because of increased ocean and surface temperatures. New evidence from ice core tephra shows that subglacial volcanism can breach the surface of the ice sheet and may pose a great threat to WAIS stability. Micro-CT analyses on englacial ice core tephra along with detailed shard morphology characterization and geochemical analysis suggest that two tephra layers were derived from subglacial to emergent volcanism that erupted through the WAIS. These tephra were erupted though the center of the ice sheet, deposited near WAIS Divide and preserved in the WDC06A ice core. The sources of these tephra layers were likely to be nearby subglacial volcanoes, Mt. Resnik, Mt. Thiel, and/or Mt. Casertz. A widespread increase in ice loss from WAIS could trigger positive feedback by decreasing ice mass and increasing decompression melting under the WAIS, increasing volcanism. Both tephra were erupted during the last glacial period and a widespread increase in subglacial volcanism in the future could have a considerable effect on the stability of the WAIS and resulting sea level rise.

    • David L. Hagen

      Why do climate change scenarios return to coal?
      Justin Ritchie, Hadi Dowlatabadi, Energy 140 (2017) 1276e1291

      The following article conducts a meta-analysis to systematically investigate why Representative Concentration Pathways (RCPs) in the Fifth IPCC Assessment are illustrated with energy system reference cases dominated by coal. These scenarios of 21st-century climate change span many decades, requiring a consideration of potential developments in future society, technology, and energy systems. To understand possibilities for energy resources in this context, the research community draws from Rogner (1997) which proposes a theory of learning-by-extracting (LBE). The LBE hypothesis conceptualizes total geologic occurrences of oil, gas, and coal with a learning model of productivity that has yet to be empirically assessed. This paper finds climate change scenarios anticipate a transition toward coal because of systematic errors in fossil production outlooks based on total geologic assessments like the LBE model. Such blind spots have distorted uncertainty ranges for long-run primary energy since the 1970s and continue to influence the levels of future climate change selected for the SSP-RCP scenario framework. Accounting for this bias indicates RCP8.5 and other ‘business-as-usual scenarios’ consistent with high CO2 forcing from vast future coal combustion are exceptionally unlikely. Therefore, SSP5-RCP8.5 should not be a priority for future scientific research or a benchmark for policy studies. © 2017 Elsevier Ltd. All rights reserved.

  7. “The bottom line is that the sea level rise will continue to rise in the 21st century, probably at a rate more than 8 inches observed in the 21st century”
    Surely you meant “observed in the 20th century”.
    Great read, this is a very useful, informative piece, thank you. Some of my friends/colleagues in the oil/gas engineering field have still not read/studied the latest IPCC report(s)

  8. With a range of possible values growing to 4 W/m2 by 2100, future emissions are the biggest single factor in climate uncertainty, and this is the only one that is up to us.

    • Emissions are much more likely to peak within decades with a broad mix of emergent technologies across sectors and gases – including modular nuclear and improvements in land management. A much swifter decline than RCP 2.6 thereafter is in keeping with the creative destruction dynamic of capitalism.

      The planet tends vigorously to maximum entropy at energy equilibrium at toa. The most significant planetary response to mooted forcing is exponentially (x^4) negative. Radiative imbalances decline exponentially. The most significant source of radiative imbalances in the satellite era are caused by cloud changes associated with changes in ocean and atmosphere circulation. These give changes in the planet’s energy budget much larger than the total mooted anthropogenic forcing – let alone what remains after the planet responds.

  9. Reblogged this on Climate Collections.

  10. Adding to uncertainty this paper identifies a process whereby meltwater fills up pores in the Greenland Ice Sheet altering the mass reaching the ocean.

    This is one of 2 papers forcing on the complexity of projecting contributions to SLR from the Ice Sheet.

  11. I assess great bodies of water and their levels by sitting on the shore, watching, watching for a long time. The highest water levels have been at the Bay of Fundy, told to me to be 56 feet from high tide to ebb flow. More than 1000 miles South, in the middle of the Florida Keys archipelago, near Marathon, the water on a still moonlight night moves imperceptibly. Only the unveiling of a tuft of seagrass marks the tidal flow.

    It seems to me that people have adapted to such water levels rise and fall, settling where, on average, they can live, love and let live, mostly without getting their feet wet. And, at times, when the rains cascade down or the winds blow, people scurry to high ground and wait until water levels return to what they recently had been.

    Of course, if one were really distraught by all the news of calamity by sea level rise, why not book passage on one of the 5,000+ passenger cruise liners. On such, one can ride the impending rising tides with one of those umbrella topped tropical drinks in hand while listening to Jimmy Buffett waft the air. Such ships are relatively shallow draft and can navigate estuaries if needed. Convenient for changing ports of call.

  12. Net retreat of Antarctic glacier grounding lines


    Grounding lines are a key indicator of ice-sheet instability, because changes in their position reflect imbalance with the surrounding ocean and affect the flow of inland ice. Although the grounding lines of several Antarctic glaciers have retreated rapidly due to ocean-driven melting, records are too scarce to assess the scale of the imbalance. Here, we combine satellite altimeter observations of ice-elevation change and measurements of ice geometry to track grounding-line movement around the entire continent, tripling the coverage of previous surveys. Between 2010 and 2016, 22%, 3% and 10% of surveyed grounding lines in West Antarctica, East Antarctica and at the Antarctic Peninsula retreated at rates faster than 25 m yr−1 (the typical pace since the Last Glacial Maximum) and the continent has lost 1,463 km2 ± 791 km2 of grounded-ice area. Although by far the fastest rates of retreat occurred in the Amundsen Sea sector, we show that the Pine Island Glacier grounding line has stabilized, probably as a consequence of abated ocean forcing. On average, Antarctica’s fast-flowing ice streams retreat by 110 metres per metre of ice thinning.

    • Too bad pay walled. Would have been interesting read. “Abated ocean forcing” something I would have liked more details on since warm water is public enemy number 1.

  13. Here’s a graph of measured sea-level at San Francisco (in blue), with a quadratic regression (calculated starting from the month after the 1906 earthquake, to avoid questionable data) through January, 2018, and extrapolated to 2100, juxtaposed with CO2 (in green):

    Here’s an enlarged, interactive version of the same graph:

    The red line is the linear trend; the solid orange line is the quadratic trend, and the dotted orange lines are the 95% confidence interval for the quadratic trend.

    As you can see, the rate of sea-level rise has not increased. The quadratic regression calculates an acceleration of −0.00296 ±0.01385 mm/yr². (The minus sign means deceleration, but it isn’t statistically significant.)

    There has been no acceleration at all in the rate of sea-level rise at San Francisco since the 1906 earthquake.

    That’s that’s perfectly typical for coastal sea-level measurements. Most show no significant acceleration since the 1920s or even earlier. Here are a couple of other sites with particularly high quality measurement records:

    In fact, in some places sea-level isn’t rising at all. The global average rate of sea-level rise is so slow that in many locations it is exceeded by local vertical land motion. That’s the case at Stockholm, Sweden, where accelerated sea-level rise would be beneficial, because it would reduce their expenses for dredging. Unfortunately for Stockholm, the rate of sea-level fall is not noticeably decreasing:

    At most measurement sites, sea-level is rising no faster now, with CO2 above 400 ppmv, than it was nine decades ago or more, with CO2 level 100 ppmv lower, and the average rate is only about 1½ mm/year (6 inches/century).

    Climate activists typically ignore that fact, and cite higher rates of sea-level rise, from satellite altimetry measurements. But satellite altimetry measurement records are much lower quality and shorter duration than coastal tide-gauge measurements, and they cannot measure sea-level at the coasts (the only place where sea-level matters). Citing only satellite altimetry measurements and ignoring the vastly superior coastal sea-level measurement record is the worst form of cherry-picking: it’s picking the rotten, wormy cherries in preference to the best ones.

    Since precise measurements of CO2 began in 1958, CO2 levels have risen every year year for fifty-nine consecutive years, from 315 ppmv in 1958 to 407 ppmv now, totaling a 29% increase, with no detectable effect on the rate of sea-level rise.

    That is iron-clad, indisputable proof that CO2 emissions do not significantly effect sea-level.

    That fact is surprising to many people, because they think that warming “simply must” cause accelerated sea-level rise, and the Earth’s climate has certainly warmed over the last century. Their confusion is usually because they’re only aware of three climate-related factors which affect sea-level: melting, glacier calving, and thermal expansion.

    In fact, those aren’t even the most important.

    There are at least eight factors which significantly affect global sea-level:

    1. snowfall
    2. sublimation of grounded ice
    3. melting of grounded ice
    4. glacier calving
    5. thermosteric changes (thermal expansion)
    6. vertical land movement, including post-glacial sinking of the ocean floor
    7. groundwater extraction
    8. water sequestration behind dams and in natural lakes

    #5 on that list (thermosteric change / thermal expansion) is a special case, because thermal expansion of water in the upper layer of the open ocean (which is where most ocean warming occurs) causes strictly-local sea-level rise, only. Because gravity balances mass, not volume, such “sea-level rise” causes no net lateral flows of water, and doesn’t affect sea-level elsewhere. Thermal expansion in the upper layer of the open ocean causes sea-level rise which affects satellite altimetry measurements, but does not affect coastal sea-level.

    #7, groundwater extration, is anthropogenic, but not climate related. It increases the rate of sea-level rise, and should be expected to cause a slight acceleration in sea-level rise, because rates of groundwater extraction are believed to be increasing.

    #8, water sequestration in reservoirs and lakes, is also mostly anthropogenic, but it reduces the rate of sea-level rise. However, it also should be expected to cause a slight acceleration in sea-level rise, because most of the big dams were built and filled in the mid-20th century, and the rate of water sequestration has declined since then, but dam-building obviously is not climate-related.

    #1 through #4 are the four factors which affect ice sheet mass balance in Greenland and Antarctica: snowfall, sublimation, melting, and glacier calving. The most important of those factors is snowfall. (If anyone reading this didn’t know that, it is probably because the sources you read only mention factors that cause ice mass loss, which means that you’ve been reading propaganda, rather than unbiased science.)

    In both Greenland and Antarctica, snowfall is the most important of those four factors. In fact, in Antarctica, snowfall accumulation is approximately equal to the sum of the other three factors.

    The magnitude and importance of snowfall on ice sheet mass balance (and thus sea-level) is illustrated by the story of Glacier Girl.

    She’s a WWII Lockheed P-38 Lightning which was extracted in pieces from beneath 268 feet of accumulated ice and snow (mostly ice), fifty years after she made an emergency landing on the Greenland Ice Sheet.

    Do the arithmetic and you’ll calculate an astonishing number: more than 5 feet of ice per year, which is equivalent to more than seventy feet of annual snowfall!

    That ice and snow represents evaporated water, mostly from the Arctic and North Atlantic Oceans, which then fell as ocean-effect snow on the Greenland Ice Sheet.

    The story of Glacier Girl is fascinating. You can read more about it here:
    and here:

    So, the key question is: what happens to snowfall in a warming climate?

    The answer is that it increases, for two reasons.

    First, it increases simply because warmer air holds more moisture. Every meteorologist knows that the biggest snowfalls occur when the temperature is not too far below freezing.

    Second, a warmer climate should reduce sea-ice extent, increasing evaporation from the Arctic, North Atlantic, and Southern Oceans, and thereby increasing Lake/Ocean-Effect Snowfall (LOES) downwind. (Ice-covered water does not produce LOES.)

    When additional snow falls on ice sheets and glaciers, in adds to ice mass accumulation and subtracts from sea-level.

    Warmer temperatures do not necessarily melt ice sheets and raise sea-level. Where ice sheets or glaciers are near 0°C, or the ice is grounded below the ocean’s waterline, warmer temperatures can, indeed, accelerate melting. But most of Antarctica averages more than 40° below zero, so it is in no danger of melting from a few degrees of warming. Only in southern Greenland, on the Antarctic Peninsula, and where ice sheets are grounded below sea-level and in contact with the ocean, is significant melting even plausible.

    So, we know that in a warming climate there are some factors which increase sea-level, and other factors which reduce sea-level. There’s no fundamental reason to suppose that either of those will dominate the other by a large margin.

    We can, however, draw upon the historical record, to gain insight. At the best tectonically stable locations, sea-level has been rising at about 1½ mm/year (6 inches per century) since the 1920s or before, with no sign of significant acceleration due to rising CO2 levels. At San Francisco, sea-level rise is just slightly more rapid, at 2.0 mm/year (8 inches per century), but, again, with no sign of acceleration.

    So the best estimate of sea-level rise at San Francisco by 2100 is simply a linear extrapolation of the current linear sea-level trend: 2.00 mm/yr × 82 years / 25.4 mm/inch = 6.5 inches.

    For planning purposes, it might be wise to use the upper end of the 95% confidence interval.
    Using the linear trend, that would be (2.00 + 0.20) mm/yr × 82 years / 25.4 mm/inch = 7.1 inches.
    Using the upper quadratic regression confidence interval, it’s 0.276 meters = 10.9 inches.

    None of those numbers are frightening, and none of them can be blamed on the oil companies.

    Unfortunately, we live in an extremely unscientific age, in which the chattering classes take seriously nonsense like “science without intersectional feminism is white supremacy,” “science is a social construct rooted in colonialism” and “assemblage criticism of argument expressions within a post-dialectical framework,” and such gibberish is sometimes even taught in the universities. I hope Judge Alsup (the judge presiding over the San Francisco & Oakland lawsuits against the oil companies) has not been poisoned by such mind pollution.

    • Thanks for this analysis. Part VII will be coastal US sea level rise

      • Robert I. Ellison wrote, “Mass loss is the net of snowfall and melt.”

        …plus sublimation and glacier calving.

        In both Greenland and Antarctica, ice accretion from snowfall exceeds ice loss from melting. But Greenland is still experiencing a slight net loss of ice each year, because of glacier calving, says DMI.

        Those two graphs are misleading, too. They’re from the “land ice” page on JPL’s notoriously politicized “climate vital signs” site, run by their “Earth Science Communications Team,” which consistently cherry-picks data and studies to exaggerate the negative effects of climate change, and never gives needed context which would show that the effects are negligible.

        For instance, DMI estimates that Greenland loses only about 200 Gt of ice in an average year, but that JPL “vital signs” graph shows nearly 300, and doesn’t mention that even that larger number is the equivalent of only about 3¼ inches of sea-level rise per century.

        Likewise, that JPL “vital signs” page shows Antarctica losing 127 Gt of ice per year, and never mentions that even some of NASA’s own studies show Antarctica gaining, rather than losing, ice, nor that 127 Gt/year of ice would cause only 1.4 inches of sea-level rise per century.

        Based on ICESat and ERS Zwally et al (2015) found Antarctica is gaining ice (also albeit at a glacially show rate). Here’s an article about it:
        Here’s the paper:

        Based on CryoSat, McMillan (2014) found Antarctica is losing 79 to 241 Gt/yr of ice, though that was based on only 3 years of data.

        Based on GRACE, Shepherd (2012) concluded that Antarctica ice mass change since 1992 has averaged -71 ±83 Gt/yr, which means they couldn’t tell whether it’s actually gaining or losing ice mass.

        Based on ICESat, Zwally (2012) found that Antarctica is gaining ice mass: +27 to +59 Gt/yr (averaged over five years), or +70 to +170 Gt/yr (averaged over 19 years). Here’s a presentation about it:

        The range from those various studies, with error bars, is from +170 Gt/yr to -241 Gt/yr, which is equivalent to just -0.47 to +0.67 mm/yr sea-level change, i.e., less than 3 inches of sea-level change per century.

        In other words, though we don’t know with certainty whether Antarctica is gaining or losing ice, we do know that the rate, either way, is very slow, and much slower than common coastal processes like erosion and sedimentation.

        But you’ll never learn that from the JPL Earth Science Communication Team. In extremely tiny print, they give absurdly tiny uncertainty intervals, and their graphs, based solely on GRACE, don’t show uncertainty intervals at all.

        What’s more, GRACE (may it Rest In Peace) didn’t measure ice. It measured only gravity.

        When magma shifts as the Earth’s crust rises or sinks, perhaps due to changes in the loads upon it, if affects the Earth’s gravity field just like ice accumulating or diminishing does. GRACE can’t tell the difference.

        So the GRACE-based studies must adjust their gravity measurements to account for PGR.

        Unfortunately, PGR is not reliably measurable. So they use model-derived estimates of what they think PGR probably should be.

        And, guess what? GRACE did not measure a declining Antarctic gravity field, from diminishing ice mass. It actually measured a (slightly) increasing gravity field. All of the ice mass loss “measured” by the GRACE studies was actually due to the calculated PGR adjustments.

        (“It’s models all the way down.”)

        BTW, did you notice that the two graphs both show “Rate of Change” at the tops? Well, the JPL Earth Science Propaganda Team also has a similar-looking page on sea-level, here:

        That one also has two very similar-looking graphs, but there’s a difference. On the sea-level page they only show a “Rate of Change” above the top graph. Extra credit if you can figure out why.

      • I deliberately ignored ablation and calving – as more minor processes.

        “In Greenland, the great melt is on. The decline of Greenland’s ice sheet is a familiar story, but until recently, massive calving glaciers that carry ice from the interior and crumble into the sea got most of the attention. Between 2000 and 2008, such “dynamic” changes accounted for about as much mass loss as surface melting and shifts in snowfall. But the balance tipped dramatically between 2011 and 2014, when satellite data and modeling suggested that 70% of the annual 269 billion tons of snow and ice shed by Greenland was lost through surface melt, not calving. The accelerating surface melt has doubled Greenland’s contribution to global sea level rise since 1992–2011, to 0.74 mm per year.”

        You will have to excuse the gushing prose.

        Tom and Jerry will be sorely missed – but long live GRACE-FO.

        The instruments precisely measure the distance between them changes in which occur with changes in Earth mass below. In hydrology they provide unheralded opportunities for water resource management. For ice sheets – with non-trivial PGR calculations – the results are about right.

      • Robert I. Ellison cited a 2017 Sciencemag article entitled, The great Greenland meltdown.”

        “News” stories aren’t always all that “new,” and Science Magazine has become shockingly politicized and unreliable. That Feb. 23, 2017 article appears to have been written the previous summer.

        By the time the ScienceMag article came out, the Greenland ice sheet mass balance had been running way above average for over four months.

        Here’s an article from DMI about the surprisingly high ice mass balance in Greenland for the 2016-2017 “glaciological year” (September-August):

        Here’s JPL’s attempt to “spin” it:
        The JPL article concludes:

        “if the Greenland Ice Sheet could put on 44 billions tons of ice each year going forward, it would take 82 years to get back to its 2002 self.”

        That “About Earth Only” (Art Mark) video is “fake news,” too. According to the DMI, the Greenland Ice sheet is losing an average of only about 200 Gt of ice per year. (Other estimates vary, but range up to about 300 Gt/year.) Contrary to that propaganda video, that is not enough to make global sea-level “1 to 4 feet higher by 2100.” 200 Gt/year is only enough to make global sea-level 1.8 inches higher by 2100.

      • Science Mag. produced a nice graphic of ice melt processes and it seems to be substantially right in nominating melt as the dominant process in Greenland mass loss. It’s not all that meaningful a quibble from Dave – and ones year’s variability does not a dynamic make.

        “Since at least 2002, the total mass budget has been substantially negative (on average from 2002 onwards it has lost -200 to -300 Gt per year). This year, thanks partly to ex-hurricane Nicole’s snow and partly to the relatively low amounts of melt in the summer, we estimate the total mass budget to be close to zero and possibly even positive. Greenland on average loses around 500 Gt of ice each year from calving and submarine melt processes. If we subtract this from our figure of 544 Gt for the SMB it would suggest Greenland gained a small amount of ice this year. However, compared to the approximately 3600 Gt of ice, corresponding to 1cm of global average sea level rise that Greenland has lost since 2002 this year’s slightly positive balance does not add much extra.”

        From Dave Buton’s link. The rate of loss from NASA’s sea level portal is 286 +/- 21 Gt/yr. This is within the bounds of estimates – and Tom and Jerry had an unrivaled precision. GRACE-FO will be even better.

    • Daveburton
      Thank you for this informative comment. However, the remark on your #5, the thermal expansion, is wrong. Gravity does not “balance mass”. The main change with height of the local gravity potential comes from the 1/R dependence of the contribution from the bulk of the Earth’s mass, where R is the distance to the Earth’s center. Imagine that suddenly the density of water were reduced by a factor 2. Locally, the sea level would rise by up to 10 km without lateral flow. Do you really believe that this situation would be stable?

      • [Sorry about the botched </a> tag… trying again… Dr. Curry, you can delete the botched one, if you wish!]

        I wrote, “#5 on that list (thermosteric change / thermal expansion) is a special case, because thermal expansion of water in the upper layer of the open ocean (which is where most ocean warming occurs) causes strictly-local sea-level rise, only. Because gravity balances mass, not volume, such “sea-level rise” causes no net lateral flows of water, and doesn’t affect sea-level elsewhere…”

        jens ulrik andersen replied, [that] is wrong. Gravity does not “balance mass”. … Imagine that suddenly the density of water were reduced by a factor 2. Locally, the sea level would rise by up to 10 km without lateral flow. Do you really believe that this situation would be stable?”

        Jens, the key word is “net.” That situation would cause no net lateral flow, and would not affect sea-level beyond the boundaries of the area where density was reduced.

        What would happen is a circular flow at the boundaries, with surface water flowing away from the elevated area of reduced density, and exactly the same mass of higher-density water flowing into the area of reduced density, at depth. The net effect is a gradual spreading of the area of reduced density, but no effect on sea-level beyond where that spreading occurs.

        In the real world, of course, water density does not get reduced that much, but if an area of ocean surface water warms by about 3°C, its density will be reduced by about 0.1%, and it will, indeed, bulge up proportionately.

        If there were a barrier to prevent flow between the two areas, it would be perfectly stable with the low-density liquid’s surface higher than the high-density liquid’s surface, as in this demonstration:

        Alternately, if the low-density water is frozen, that will also prevent flow between the two areas, just as effectively.

        OTOH, if there’s no barrier, and the water is liquid, then along the boundaries of the warm (low-density) section there will be a slight more-or-less rotational flow, a mixing action between the warm and cold waters. The warmer water flows away from the warm section at the surface, and the cooler, denser return flow is toward the warm section farther down. That slight rotational flow works to gradually spread the warm spot (as does normal ocean wind and wave action), but the flows to and from the warm section are balanced, so there’s still no net flow of water away from the warm spot, and no effect on sea-level at distant harbors. Sea-level is affected only where the water is warmer.

        The spreading action is gradual, though. If your warm spot is 1/3 the size of the Indian Ocean, the temperature-driven flows at its boundary have negligible effect on the size of the warm spot, over a reasonable amount of time.

        If you somehow had a transient condition in which warm water was side-by-side with cold water, yet their surfaces were at the same height, what do you think would happen? The answer is that the force of gravity would be greater on the denser cold water, than on the less-dense warm water. That would cause the cold water surface to sink, and the warm water surface to rise, until the force of gravity was equalized between them, thus creating the warm bulge.

        So if you warm a section of the ocean, it will rise up, in place, just as happens if you freeze a section of it. The lower the density is the higher the sea-level will be, but only where the water warms. The water doesn’t affect sea-level far away, because there is no net lateral flow of water away from the “bump.”

        It’s not hard to calculate the surface height differences. The difference in depths is proportional to the difference in density.

        For example, suppose that an few million square-mile section of surface water in the Indian Ocean, 100 meters deep, were heated until its average density was 0.1% lower than the density of the surrounding ocean water. (It would need to be about 3°C warmer, on average, than the surrounding water.) All other factors being equal, that warmer water would rise up 100 meters / 0.1% = 10 cm.

        Gravity balances mass, not volume, so the force of gravity on the warm water would be exactly the same as on surrounding denser water, so there would be no net lateral flow as a result of the expansion of the warm water, and the surface height in the warm patch would remain ≈10 cm higher than the surrounding ocean as long as the water remained ≈3°C warmer than the surrounding cooler part of the ocean.

        At the boundaries, there would be a slight rotational flow working to gradually spread the warm spot, but the sea surface heights would not equalize before the temperatures equilized.

      • Daveburton, the reply link is missing on your response so I write a response to my own comment.

        Your long response has not convinced me of your claim that a thermal expansion of the ocean will not be felt at the coast but only in regions with large depth. For example, the analogy to the equilibrium between columns of different density is false since here the condition for equilibrium is equal pressure at the bottom. For the warming sea the condition is constant gravitational potential at the surface. This implies that there will be a net lateral flow from regions with warming and expanding water. Let me show this by a simple calculation.

        Assume that in an area with depth d there is an average change drho of the density rho and hence – without lateral flow – a rise h~(drho/rho)d of the sea level. For initial perfect spherical symmetry of the Earth, with radius R and mass M, the corresponding change of the surface gravitational potential is dV=kappa h(M/R^2), where kappa is the gravitational constant. The symmetry is broken by the local expansion of the water but this does not change the result. If the lateral dimension of the heated area is large compared with the depth d, the expanding water may be approximated by a number of thin, planar layers parallel to the surface, and the force from such a layer is independent of the distance from the plane (as the electrostatic force in a parallel plate capacitor). The work performed by the forces from the layers during the motion h of the unit mass at the surface is therefore the same as for the same motion without expansion of the water.

        So there must be net lateral flow of water to restore the equilibrium. There will remain a small bulge of water above the hot area but the height of the bulge will be vastly smaller than the value h given above, by a factor of order d/R. To a good approximation, the rise of the sea level due to thermal expansion will be the same at the harbors as in the middle of the ocean.

      • jens, that is incorrect. If your layers are not thicker in the low-density section than in the high-density section, then the force of gravity will be less on the low-density layers, resulting in less water pressure beneath them. That will cause water from the colder, high-density region, which is at higher pressure, to move into the lower-pressure warm section, lifting the sea surface until the pressures are equalized.

        Do you understand that the pressure beneath a layer of water is determined by the weight of the water above it?

        Consider a “flat” region of the ocean (well, actually, part of a sphere, with the center of the sphere being the center of the Earth). Let us stipulate that, initially, the entire region of ocean has exactly the same temperature profile, and there are no waves or currents.

        Let R be the distance between from the center of the earth to a point which is nominally 100 meters below the surface of the ocean.

        The surface of the sea is at R+100 meters from the center of the Earth.

        Now , warm the top 100 meters of that section of ocean by enough to decrease its density by 0.1% (about 3°C). That section becomes 0.1% thicker, raising sea-level there by 10 cm, becoming R+100.1 meters.

        Now, you imagine that the raised warm water at the surface will “run downhill,” lowering sea-level in the raised section. That’s partially true, but you cannot ignore what happens below the surface. That lateral surface flow away from the warm area reduces the thickness of the warm section of water, and thereby reduces the water pressure beneath the warm layer, at 100 meters depth, and increases the cold water pressure adjacent to it. That causes colder water from adjacent to the warm region to flow into the warm region, until the pressures are equalized, meaning that the weight of the water above is equal.

        You can’t have less water weight in the warm section than in the adjacent cold section without causing water to flow from the cold section into the warm section, to equalize the water pressures. Until the weight of the water above the warm section is equal to the weight of the water above the cold section, the higher pressure at level R in the cold section, and the lower pressure at level R in the warm section, will cause water to flow from high pressure to low, i.e., from cold section to warm section.

        That means warming a region of the surface of the ocean causes no net lateral flow of water. There is a bit of current from warm to cold at the boundary between them at the surface, balanced by an exactly equal flow from cold to warm at depth. All that circular flow does is slowly spread the boundary between warm and cold sections. There can be no net flow either away from or into the warm section, and thus zero effect on distant harbors.

      • Daveburton
        you are confusing two different instabilities. In equilibrium both the gravity potential at the surface must be constant and the vertical profile of density must be the same. Differences in the vertical density profile will, as you say, give rise to rotational flow. Deep water will flow from regions with high pressure to regions with low (warmer water above). This will raise the surface in the warmer region and water will flow out of this region near the surface to maintain a constant gravity potential.

        To avoid this confusion consider a situation with the same warming as a function of depth everywhere. There is then no instability of the first kind, leading to rotational flow, but the increase in sea level due to the expansion will be larger in the deeper sea, leading to a net flow of water from deeper to shallower regions and establishing close to the same rise of the sea level everywhere.

      • jens wrote, “you are confusing two different instabilities. In equilibrium both the gravity potential at the surface must be constant and the vertical profile of density must be the same.”

        “Equilibrium” is when there’s no temperature difference (no more warm and cold sections, just tepid everywhere). As I wrote above, “sea surface heights would not equalize before the temperatures equalized.”

        Until then, as I wrote above, “the difference in depths is proportional to the difference in density.” The warm bulge will not sink as long as the warm area remains warmer than the rest of the ocean.

        Thermal expansion of water in the upper layer of the open ocean (which is where most ocean warming occurs) causes strictly-local sea-level rise. Such sea-level rise occurs only where the water warms. Such localized sea-level rise affects the satellite altimetry measurements, but it does not affect sea-level elsewhere, because gravity balances mass, not volume.

        jens continued, “consider a situation with the same warming as a function of depth everywhere… the increase in sea level due to the expansion will be larger in the deeper sea, leading to a net flow of water from deeper to shallower regions…”

        That’s why I wrote “in the upper layer” of the open ocean.

        If water at the bottom of the ocean expands, it has an effect similar to raising the ocean floor, which raises sea-level everywhere.

        However, in practice, there’s not much of that. Most ocean warming is surface warming.

        Even in the very long term that is likely to remain the case, thanks to natural thermostat mechanisms.

        As the “Atlantic conveyor” carries warm surface water north, evaporation removes heat from the ocean and carries it up to the clouds. The warmer the water is, the faster the heat is removed from it (negative feedback).

        Additionally, near Greenland, where the cooled water finally sinks to the ocean depths and begins its long return voyage south, a warmer climate causes reduced sea ice coverage, which accelerates evaporative cooling of the water (more negative feedback). (It also increases ocean-effect snowfall on the Greenland ice sheet, offsetting meltwater losses.)

        So “global warming” won’t warm the ocean depths very much. In fact, until Josh Willis “fixed” it, the Argo data showed no deep ocean warming, at all. (Like everyone else, scientists are often very good at finding what they’re looking for, and not very good at finding what they aren’t looking for.)

    • Dave Burton – thanks for understandable, plain English discussion.

    • Australia has eight locations with at least 50 years of sea-level measurements, which NOAA has analyzed. In the following table, all the figures are from NOAA, except Sydney:

      Cst-Stn  PSMSL   Station name               Start   #years  Trend     CI
      -------  -----   -----------------------   -------  ------  -----    ----
      680-140   196    Sydney, Fort Denison 2    1886.96  129.08   1.16    0.17
      680-471   111    Fremantle                 1897.04  119.00   1.70    0.25
      680-051   637    Townsville I              1959.04   57.00   1.91    0.38
      680-073  1154    Bundaberg, Burnett Heads  1966.12   49.92   1.37    0.51
      680-078   822    Brisbane (W. Inner Bar)   1966.12   49.92   0.89    0.62
      680-021  1157    Weipa                     1966.04   50.00   3.52    1.30
      680-479  1115    Carnarvon                 1965.87   50.17   2.91    1.47
      680-494   189    Port Hedland              1966.04   50.00   2.26    1.59

      Note: Sydney’s linear trend is calculated starting in 1931 (1930 + a gap in the data). If the full record is used (as NOAA did in their analysis), a smaller SLR trend is found, because there was a slight acceleration in rate in the 1920s.

      The average rate at the eight locations is 1.97 mm/year (8 inches per century). The highest rate is 3.5 +/- 1.3 mm/year, at Weipa. Click on any station number to view the graphs, etc., including links to the NOAA and PSMSL pages.

      None of the eight locations has a measured sea-level trend in the 4.4 to 6.4 mm/yr range, though the high end of Weipa’s 95% CI does barely make it into that range.

    • Clutch 2017 and pray for it to come back to life.

      • Instead of preaching at us no-account incorrigible deniers, the time and efforts of our resident nagging alarmists might be better spent haranguing the do-nothing signatories of the Paris Non-Binding Pretend Accordian.

        I would be happy to sign a non-binding pledge to limit the temperature increase to 1.5 °C above pre-industrial levels, if you all would go away. Aw shucks, I’d be willing to go as low as .7 °C. (I hope I haven’t given away my negotiating position).

  14. “What is needed, then, is to add some “freeboard” to policies and practices already in play, or that should be in play, to account for the negative effects likely to be associated with climate change and/or population growth. Even if coastal populations do not add the needed freeboard to those things they need to do to adapt to the current rigors of coastal living, this much is clear: if they simply put into place those policies and practices currently advocated by leading hazard management practitioners, they will have taken giant steps toward adapting to future changes brought about both climate change and population growth.”

    There are a plethora of techniques for building both societal and environmental resilience on coasts. A foot or two of freeboard above the most extreme event makes little difference to coastal engineering.

  15. Issues.
    1. “A key issue is the uncertainty of sensitivity of climate models to CO2. The equilibrium climate sensitivity is a measure of the climate system response to sustained radiative forcing defined as the amount of warming in response to a doubling of atmospheric CO2 define.”

    “These simulations are coordinated by the CMIP (Coupled Model Intercomparison Project),”

    “The average value of equilibrium climate sensitivity for climate models used in the 21st century projections is 3.2oC, with a range 2.08 to 4.67oC. [AR5 WG1 Chapter 12, Box 12.2]”

    There is no uncertainty at all with climate models once they have been run for a number of years. Say 18 years for example 2000 – 2017. Every one of these models has a known emergent ECS [see last comment]. The key issue is the unreasonably high ECS emerging from these models which forces them to run high.

  16. Issues.
    2. “the projections out to 2100 that use climate models that do not include the lower values of climate sensitivity that would produce warming that is substantially smaller than the climate model values.”
    ” recent rates in the observational record (e.g., ~0.26°C per decade for 1984–1998 and ~0.04°C per decade for hiatus period 1998–2012).”
    I.e. 0.11 C per decade.
    “The CMIP5 5 to 95% ranges for GMST (global mean surface temperature) trends in the period 2012–2035 are 0.11°C to 0.41°C per decade.”
    At least they include the average for the last 40 years as the lower bound, very humorous.

  17. Issues.
    3. “Most of the extra ice during glacial times existed in North America and northwestern Eurasia. These ice sheets were highly sensitive to climate change, as witnessed by the fact that they existed during ice ages and were almost entirely absent during interglacials. Both the size and sensitivity of these glacial ice masses would have been conducive to high deglacial rates of SLR”
    When we have presumably only a 10th of the glacial ice [Northern] and presumably a similar figure down south it seems amazing to see dire predictions when all the heavy melting and sea level rise was done milleniae ago. Not only is there only an ice cube left to melt in comparison, the top of the bath tub has enlarged in surface area and volume.
    There is no way that what is left can ever contribute to any significant SLR.
    There is an upper limit if it all melted, it slows down as we get closer, not accelerates.

  18. Pingback: Something for the weekend #7 – 2020: Tracking Optimism

  19. The thing that amuses me is the amount of work that has gone into producing probability distributions for sea level rise within RCPs, and the total resistance to trying to assess the probability distributions across concentration pathways.

    Table 2 is actually useless for decision making since the reported probabilities tell us very little. The charitable view is that climate scientists view the problem of assigning probabilities to the assumptions underpinning pathways as outside their domain of competence. But they are well within the competence of others and I’m sure affected communities would welcome the assessment.

    One specific example is that Antarctica sea ice studies are largely predicated on RCP8.5. The prognostications may increase the consequences of extreme concentration pathways, but it remains pretty unlikely.

  20. Pingback: PICTORIAL Guide To Sea-Level Rise Alarmism And Observed Reality | Climatism

  21. This paper discusses the potential impacts of tropical Pacific circulation variability on West Antarctica ice shelves. Due to bathymetry this region may be uniquely set up to be influenced by changes in the depth of the thermocline of local waters. Figure 5 depicts such variability at depth.

    • This paper has a map with temperature variability of waters along the shores of Antarctica. Ties in with other papers depicting changes in depth of thermocline on multiple time scales. Obvious correlation with unstable glaciers and ice shelves.

      • Coauthor. Try to keep up.

      • My link is more recent. I already provided a similar link by other authors months ago. I provide this information for your comrades who are either oblivious to or willingly ignorant of all evidence which screams natural variability. Just as they want to ignore the possible role of geothermal activity in West Antarctica and Greenland. Even now, most analyses and models ignore recent findings that geothermal flux is higher than previously thought in both West Antarctica and Greenland. Studies already mentioned by Judith and myself also show links to warm water in Greenland fjords affecting marine terminating glaciers and geothermal flux in West Antarctica exhibiting temporal variability. These are major findings since this adds to the level of uncertainty if the focus has been on only AGW as having a role of thinning glaciers and ice shelves.

        It now should be obvious why the West Antarctica glaciers and Ice Sheet are inherently unstable. When ice sits in water atop volcanic geology, weird things happen. Of course, reading only the complicit MSM, one would never understand the complexity of all factors involved.

      • Nobody is ignorant of NV. It is you guys who hide from the warm phase of NV, and pray for the cool phase. You’ve politicized NV.

      • AMO gawd in heaven, please come and slow down the rate of 21st-century SLR.

      • If anyone longs for the emotional support of clinging to some blue but Tiffanys is out of their price range, they could always whip out one of these maps. Just like diamonds, they could be forever.

    • If you had followed E Steig, you would already know this.

  22. Connection of sea level and groundwater missing link in climate response

    “When sea level falls, ground water levels increase,” said Li. “We find that lakes increase biodiversity of pollen, and other species that liked those ecosystems flourished. When lakes decrease, the diversity of pollens and species decreases.”

    • Sedimentary noise and sea levels linked to land–ocean water exchange and obliquity forcing

      Sea-level rise is one of the most serious impacts of present-day climate change. In the Intergovernmental Panel on Climate Change (IPCC) assessment report, rising global sea level has been primarily linked to two factors related to global warming: land ice melting and the thermal expansion of sea-water48. The importance of groundwater fluctuations may be underestimated in long-term projections of global sea-level change due to lack of data or understanding of land–ocean water balance dynamics. The present-day volume of groundwater storage is equivalent to a sea-level differential of approximately 320–330 m35,36. Thus, as present-day Earth continues toward both warmer climate and lower obliquity angles, changes in continental aquifers should be reassessed for their contribution to global sea-level variations in long-term future projections.

  23. Regarding the phrase: “whereas the projections out to 2100 that use climate models that do not include the lower values of climate sensitivity that would produce warming that is substantially smaller than the climate model values.”

    That’s four “that”s in once sentence and it makes the sentence almost impossible to parse.
    Do you mean that there are projections out to 2100 that do NOT use climate models but you only wish to speak of the subset of projections those that do use climate models?
    Or of the subset of climate models that use higher values of climate sensitivity?

    • Don Monfort

      Until something better comes along, try it like this:
      “whereas the projections out to 2100 using climate models that do not include the lower values of climate sensitivity would not produce warming that is substantially smaller than the climate model values.”

      • Don Monfort

        If that is still many thats for you:

        “whereas the projections out to 2100 using climate models that do not include the lower values of climate sensitivity would not produce warming substantially smaller than the climate model values.”

        Let me know. I can get rid of the other that, if it helps.

  24. Any scenario using RCP 8.5 is a crock. BAU is something between 4.5 and 6, comparable to A1b in AR4. Any scenario based on CMIP5 is also a crock, for two reasons: all but INM-CM4 are provably running hot, and Observational ECS is about half of the 3.2 model average. Any scenario claiming future SLR acceleration has to do two things: explain the absence of acceleration so far, and the future mechanism producing it in the future. Greenland wont do as it is bowl shaped and has to melt, not calve. East Antarctica is stable/ gaining. So that leaves WAIS. But the Ronne and Ross are stable. Stuff related to subglacial volcanism like PIG in the Amundsen embayment are too small. Only by absurd assumptions about entire catchment basins lead to future acceleration. See guest posts Tipping Points and Totten Glacier for details and examples.

    • Curious George

      It is depressing to see so many highly qualified people to engage in a theoretically impossible task of determining a second derivative of a short noisy sequence. On the other hand, taxpayers pay them well for this “research”.

  25. La Niña death throes:

    Longest departure above trend in the satellite era gets its ticket punch for another season, maybe year end:

    • Alternative Nina death throes

      How’s this for an early Christmas present?
      By Christmas, we’ll still be in La Nina.

    • JCH: Longest departure above trend in the satellite era gets its ticket punch for another season, maybe year end:

      With the ups and downs since 2010, this is a bad time for forecasting.

      • Never admit there is positive phase of natural variability. The cooling is always right around the corner.

      • JCH: Never admit there is positive phase of natural variability. The cooling is always right around the corner.

        So you think short-term oscillations are a good prognostic indicator?

      • JCH’s helpful graphs seem to be auto-refreshing ones.
        It’s notable that the Nino 1+2 region is levelling off, there are signs of renewed upwelling off Peru.

      • 1900 to1990 – ~1.1 mm/ yr
        1993 – ~2.0 mm/yr
        1993 – present – 3.3 mm/yr
        last 10 years – 4.29 mm/yr
        last 5 years – 4.73 mm/yr

        up, up, uP, UP, and we have takeoff. Or, it’s the (or not): Part VI happening trench for dead enders.

      • jch

        with your post at 11.18 you have mixed early last century oranges with 21st century lemons.

        Can you please show your sources, so we can check the accuracy of your fruit supplier


      • The only place it is up, up, up, up is on somebody’s Texas Instrument hand held calculator.

        When it storms the beaches, there will be a case to be made.

        I’m not holding my breath.

      • Sources: Professor Curry’s article uses all of the same sources for 20th-century SLR.

        For satellite-era, I use AVISO.

      • The Hay paper provided nice optics for the MSM. The charts for both Fremantle and NYC depict breathtaking increases leading up to 2010 at which point the data end. The reality is that after 2010 the NOAA charts drop like rocks to 2016 and 2017.

        But what the hey, when authors need chiropractors because of their statistical contortions to get a pre-determined result of reducing the pre-1990 rise, pretty pictures do a terrific job of diverting attention.

      • JCH wrote, “For satellite-era, I use AVISO.”

        AVISO no longer produces graphs of sea-level.

        Their web site used to be able to produce graphs of sea-level measurements from satellite altimetry, but they removed that feature last year. Now they only produce graphs which are mislabeled “mean sea level,” but are actually graphs of what they think mean sea-level would be, were it not for isostatic sinking of the ocean floor (in response to the last deglaciation, circa 13,000 BC to 5,000 BC).

        I complained to them about that downgrade of their web site, to no avail. Here’s the email conversation:

        ——————- Begin message ——————-
        From: David Burton
        Date: Wed, 8 Nov 2017 03:19:19 -0500
        To: AVISO <>


        In the old version it was possible to show sea-level trends with or without Peltier’s 0.3 mm/yr GIA adjustment (like this), but in the new version this does not seem to be possible. Could you please restore this capability?

        When the GIA adjustment is added, the result is not the actual sea-level trend. Rather, it is an estimate of what the sea-level trend would have been were it not for the fact that the ocean floor is still slowly sinking under the weight of the meltwater from the last major deglaciation, circa 7K years ago. I would like to be able to produce graphs of the actual sea-level trend.

        Thank you,
        ——————- End message ——————-

        ——————- Begin message ——————-
        De : AVISO <>
        Reçu : Fri, 17 Nov 2017 09:35:16 +0100
        À : Burton, David

        Dear Dave,

        indeed on the site we have decided to distribute to the users the “oceanic climate indicator” which is the mean sea level corrected for the GIA. This decision in order to be consistent with what we do usually: it’s for example similar to compute the altimeter sea surface height taking into account the tides , or all other oceanic or atmospheric signal and the SSH is thus also not the “true” sea level. So I’m afraid you will have to decrorrect yourself the GIA correction:

        The value we take into account for the computaion of GIA is -0.3 mm/year, so the value of the trend will be: MSL_trend=MSL_trend_from_file – 0.3

        best regards

        Françoise Mertz

        Aviso User Services
        ——————- End message ——————-

        ——————- Begin message ——————-
        From: David Burton
        Date: Fri, 17 Nov 2017 09:54:37 -0500
        To: AVISO <>

        Thank you for your reply, Françoise.

        Please, at least correct the labels on your graphs. Contrary to their labels, those graphs are not “Mean Sea Level from Altimetry,” and should not be labeled as such. They should be labeled what they are: “Mean Sea Level from Altimetry plus GIA.”

        People who look at graphs of sea-level expect them to be useful for projecting actual sea-level rise (or fall, in some places). When you add a “fudge factor” like Prof. Peltier’s estimate of PGR effects, you are attempting to produce a graph which includes just some of the components of the sea-level trend, and omits others. That is useful for some purposes, but it is is not in any sense “mean sea level.”

        It is not in any sense “measured,” either! Professor Peltier’s 0.3 mm/yr GIA estimate is purely model-derived. It is unmeasurable, and unverifiable.

        Prof. Peltier’s GIA estimate doesn’t include any uncertainty estimate, either, so when it is added to any other quantity it is impossible to correctly deduce error margins for the sum.

        I suggest that you produce graphs of actual, measured sea-level trend, which include all components of that trend, and so have not been adjusted upward by 0.3 mm/yr GIA estimate.

        If you wish to also produce graphs which break that trend down into best estimates of its various components, that could also be useful for some users of your products. Such components would include major factors like steric change, grounded ice mass balance change, and PGR, and perhaps also minor factors like groundwater extraction, and dam/lake/river impoundment. (But I strongly recommend that you include error/uncertainty margins for those components, as well, and reference sources for the various estimates!)

        It is deceptive to decompose the sea-level trend into estimates of its components, and then graph just some of those components (the ones which contribute to a positive trend), and omit the main negative component, which reduces actual sea-level, and mislabel the result “mean sea level.” Doing so invites criticism that you’ve put a thumb on the scale, to exaggerate sea-level rise — which is, indeed, the effect, if not the intent, of what Aviso is now doing.

        Warmest regards,
        ——————- End message ——————-

        ——————- Begin message ——————-
        De : AVISO <>
        Reçu : Fri, 29 Dec 2017 14:17:47 +0100
        À : Burton, David

        Dear David,

        you will find herafter an answer of our experts:

        Though we understand your remark concerning the definition of Mean Sea Level, this is not the definition of the ocean surface topography science community. The objective of the AVISO indicator (and many other processing groups such as Colorado University) is to provide the mean sea level variations in order to understand the evolutions of oceanic volume change. Thus, we correct for PGR, polar tide, earth tide, load tide… because the movements of the terrestrial crust are not the focus of this indicator. These corrections are all listed with corresponding references. We do include the corresponding uncertainties in our total uncertainty assessment of 0.5 mm/yr (PGR participates by 0.05mm/yr at 90% CL). However, we will make it clearer on the website (though not in this label) that the PGR correction is applied and how to remove it.

        Best wishes for the new year
        Aviso User Services
        ——————- End message ——————-

      • it’s for example similar to compute the altimeter sea surface height taking into account the tides , or all other oceanic or atmospheric signal and the SSH is thus also not the “true” sea level. So I’m afraid you will have to decrorrect yourself the GIA correction:

        The value we take into account for the computaion of GIA is -0.3 mm/year, so the value of the trend will be: MSL_trend=MSL_trend_from_file – 0.3

        Decorrect it yourself. Too funny.

      • nobodysknowledge

        Thank you for this clarification Dave Burton. I have sometimes found it difficult to understand what is meant with sea level rise. What about calling the MSL trend Fake SLR or FSLR and the other measures True SLR to know the difference. Another problem is that the Peltier GIA adjustment probably is too high, according to some other estimates.

      • nobodysknowledge

        Let`s hear geoscientist Thomas Frederikse from the Delft University of Technology in the Netherlands about the sinking ocean floor. “The implications, according to Frederikse and his team, is that as the ocean bottom subsides elastically, the actual increasing volume of the ocean – called barystatic sea level rise – is masked from measurements based on satellite observations.”
        And further: “For roughly the last two decades (the period 1993–2014), the team calculates the increase of the total ocean load has pushed the seabed down by about 0.13 mm (0.005 inches) per year, or around 2.5 mm (almost 1/10th of an inch) in total for the period.”
        Under half of what Peltier, and other sea level gurus want us to believe.

      • nobodysknowledge

        Comment to an article in Geophysical Research Letters 2017:
        Ocean Bottom Deformation Due To Present-DayMass Redistribution and Its Impacton Sea Level Observations.
        Thomas Frederikse,RiccardoE.M. Riva, and Matt A. King

      • Thanks, nobodysknowledge, for pointing me to the Frederikse paper.

        FSLR (Fake SLR) seems like a good name for SLR+GIA, to me. 😉

        Adding model-derived GIA to the global sea-level trend is useful for some purposes, but the sum is not “sea-level rise.” Rather, it is an estimate of what the rate of sea-level rise would be were it not for post-glacial sinking of the ocean floor. In the words of Greg Goodman, “it… means their “mean sea level” is now floating, phantom like, above the waves.”

        Frederikse distinguishes the two more tactfully, by calling Real SLR “geocentric sea level rise” and Fake SLR “barystatic sea level rise.”

        But his 0.13 mm/yr figure is not an estimate of GIA. Rather, he is claiming an additional sinking of the ocean floor, in response to recent sea-level rise, which he thinks should also be added to measurements, to better estimate barystatic (fake) sea level rise.

        On page 7 he says his adjustment is in addition to “the viscoelastic response to ice mass changes in the past (GIA), which is in the order of −0.15 to −0.4 mm/yr (Tamisiea, 2011).”

      • nobodysknowledge

        Thank you for another clarification Dave B.
        This becomes almost unbelievable. According to Thomas Frederikse et al the ocean floor has subsided by 2,5 mm over 12 years because of the gradual extra load of about 30 cm water the last 250 years.

    • Must he do this dozens of times a day?

      The MEI stands at -0.73 for Jan/Feb 2018. Claus Wolter at NOAA categorizes conditions in early 2017 as a short lived El Niño – what JCH calls a La Niña. It was a La Niña Modoki – a short lived phenomenon seen as a cool pool in the central Pacific and double Walker Cells driving warm water onto both east and west margins. We shall see where the MEI goes next.

      This time of year is when ENSO changes – and predictability is especially difficult. To base prognostication on 7 day changes in weather at the ocean surface is beyond absurdity. The Pacific remains in the canonical La Niña state with elevated water levels in the west and lower levels in the east along the equator.

      Cool sea surface temperature anomalies – over considerably longer than 7 days – can be seen in the east and warm in the west.

      A near real time super computer visualization of surface pressure and winds likewise show the La Niña pattern of low pressure in the west and high pressure in the east – driving east-west Walker Circulation in the atmosphere. The SOI is positive – which is a harbinger of La Niña.

      The southern and northern annular modes (SAM and NAM) are both negative and that will spin up sub-polar ocean gyres in both hemispheres – enhancing upwelling and cooler sea surfaces in both the north and south Pacific. SAM and Nam seem modulated by solar activity but there is no simple cause and effect.

      This is an intellectual exercise I have been at for a very long time. We shall see who is right. But even if I am wrong – there is still no rational comparison to be made between at attempt to understand physical mechanisms in the system and examining 7 day old entrails.

      He has taken to tediously accusing us of neglecting the warming phases of natural variability. It is odd because the hiatus did not emerge out of nowhere. It followed a natural contribution to warming from 1976 to 1998. When considered over the 20th century – and several natural oscillations – the trend of anthropogenic warming is at most 0.1 degree C/decade. It puts ECS and the 2 degree target in a different light. I doubt that trend will continue in the 21st century.

  26. Dr Curry, Thank you again for this series of essays.

    • afonzarelli


      And we hope your therapy with your arm is coming along (’cause dat’s a whole lotta typin’… ☺)

  27. When talking about Climate Change, Risk, Uncertainty and the Burden of Proof, sometimes our best adaptation strategy may be to do nothing but, having ‘the courage to do nothing’ (what Lord Monckton says is our wisest course), is difficult for those who are paid to look useful. I think you can say the same thing about sea level change. However, if you live in California, exploring options when it comes to assuring plentiful supplies of fresh water isn’t something that you should put off until 10 years into a drought or think you can solve by telling citizens, ‘if it’s yellow, let it mellow’ and to let their lawns die.

  28. Judith

    An interesting article. Thank you.

    When someone averages out the gdp of the world there will be many countries below and above that average and the measures the countries in each group will need to take will be irrelevant to those in the other group and different between themselves.

    When I average rainfall throughout the world, those in Saharan countries or the tropics won’t recognise the values attributed to them.

    The same with temperatures, whereby averaging out misses the nuances of the many different climates that Marcel Leroux recognised decades ago.

    So this globalisation of figures in order to arrive at an ‘average’ means nothing to those presented with data that does not reflect their local circumstances.

    Consequently the most significant portion of this study is within the first few lines;

    “Observed sea level rise over the last century has averaged about 8 inches, although local values may be substantially more or less based on local vertical land motion, land use, regional ocean circulations and tidal variations.

    And this piece later on;

    “Sea level changes on Earth cannot be treated as occurring in a rigid ocean basin. Tectonics, dynamic topography, sediment compaction, prograding delta build up, ocean floor height change sub-marine mass avalanche. and melting ice all trigger variations in the configuration of the basin and ultimately impact sea level. While some of these processes operate at very slow time scales others do not and may have substantial impact on local sea level at least. Surely such changes are as ‘possible’ as a collapse of the West Antarctic ice sheet in the 21st century.”

    To truly get a handle on what is or is not happening, the ‘average’ means nothing as it is being confounded in virtually every coast line in the world by the local factors. There’s no point building a large sea wall to protect the coast line if the land locally is rising rapidly, or to build something sub standard and low if the land is falling rapidly

    To get a true picture of the overall sea level rise situation the individual circumstances of a scientifically valid number of locations representing the various ‘confounding’ factors need to be examined and not just concentrate on those where sea level change is very real but the reasons for it not properly outlined.

    Rising sea due to mans activity? A continuation of a centuries long trend? Earth sinking or rising? land use, ocean circulation, tidal variations, predominant wind directions?

    So let’s have sufficient detailed and representative studies looking at like for like circumstances of local situations, whilst bearing in mind the fluidity of the sea and the dynamic nature of it, that study needs to look back centuries, not just the satellite era.

    The study needs to look at all circumstances and be as detailed as the extremely thorough investigation of the circumstances surrounding an investigation-funded by the EU-of seven historic European temperature records under the ‘improve’ project.

    This examined the different observers and their methods, the effects of changing instruments, The growth of trees, and the cutting down of them, the erection or demolition of nearby buildings, the moving of operations from one site to another, the fact that records were often not written up for weeks.

    In the early days thermometers were often set on balconies or placed indoors. The study looked at the balconies-which were often removed, changed in height or built with different materials, and the internal temperature altered when new doors -with and without key holes- (introducing cold draughts) were put in place. Real scientific investigation in action

    Sea level change and the speed at which it is happening (or not) has become the simplification and globalisation of what is essentially a local and often complex set of factors. Averaging this all out does not tell us very much


    • If one wants to hide in lalaland, then the global rate of sea level rise does not tell you very much. If I want to know about the reality of Galveston, my local, I have to know about the situations in every ice sheet and ocean basin and every shoreline and watershed, etc. on the globe. That is how the global average is built.

      The rejection here of the VLM paper is just another case in point. According to the chickens in their hiding places, the science was insufficient because VLM was not appropriately addressed. A science team followed up on improvements in VLM and demonstrated that the tide gauges (the data for which is the work of Simon Holgate) and the satellites are in agreement on the global average, and the response is always to figure out a hole into which to hide. But Sydney! That is the point of CargoCult Etc.; to figure out ‘it’s not happening” places to hide. It’s genuinely hilarious to watch.

      • JCH

        You also learn from History. I have this rather old Book ‘The Elements rage’ On Page 17 is an excellent photo of the Galveston sea wall. Galveston has certain problems and lumping it in with an area of coastline where the sea is receding as the land is rising is truly la la land.

        Each place is unique and has different problems. How does it help to pretend that all the world is the same?


      • You add up each place, you get the global average.

        I have zero doubt that the first mention here at CargoCult Etc. of the Galveston seawall, and its history, was made by me. The seawall was first proposed after a town on the gulf disappeared in a hurricane. The city fathers of Galveston rejected building a seawall. At the time, Galveston was the Wall Street of the South: a spectacularly wealthy banking and shipping boomtown. The storm was a terrible natural disaster, and the city never recovered. But they did immediately set about building their seawall. Too late. If anybody wants to know what a 19th-century boomtown looked like, go to Galveston. The big brick buildings survived the storm, and the place has not experienced much of the 20th and 21st centuries. They happened ~35 miles up the road in Houston, which stole the wounded Galveston’s financial thunder.

      • If you live in Galveston, the global rate of sea level rise does not tell you very much. Most of Galveston’s sea-level rise is due to subsidence.

      • The long‐term rate of subsidence for Grand Isle and Galveston were determined to be 7.59 ± 0.23 mm yr−1 and 4.71 ± 0.21 mm/yr respectively. These new subsidence records can be viewed in a number of different ways. The inferred Grand Isle subsidence curve appears to experience three distinct phases. Phase 1 lasts from 1948 to 1958 and has a trend of 3.16 ± 1.0 mm yr−1. Phase 2 lasts from 1958 to 1991, and has a trend of 9.82 ± 0.33 mm yr−1, while phase 3 lasts from 1992–2006 and has a rate of 1.04 ± 0.97 mm yr−1. Galveston too can be broken into three similar sections with rates that are 2.55 mm yr−1 ± 2.15 for 1947–1958, 6.18 ± 0.34 mm yr−1 for 1959–1991 and −1.99 ± 1.41 mm yr−1 for 1992–2006.

        Galveston has red tape on groundwater mining. They started red tape on groundwater mining sometimes the 1990s.

      • Jch

        How long will it take to replenish the water that had been extracted?

        Does the land then stabilise or expand?


      • You would have to ask a competent hydrologist/geologist!!

        But I think it depends on the local formations and the timeframe. To the east and west of Galveston there is a lot of new construction, and I believe there is still subsidence occurring, but it appears the old city, which is where that tide gauge is located, is at least stabilized, which is why they, Galveston County introduced all that nasty red tape on drilling wells.

        Houston is, of course, not on the coast, so the subsidence up there is up there. Houston doesn’t believe in red tape. It’s creating an inland bowl.

      • Jch

        I found this article

        It seems to suggest that stopping the groundwater depletion can halt subsidence and that putting water back might help to plump it back up but not if it is compacted clay.

        Mind you, with the vast amounts of humans now, many living on the coast, it seems likely that subsidence will only increase in future


      • Tony

        There is a meme on the inelasticity of consolidated clay that is not strictly true. Here’s a ‘classic’ text.

        “Grim (1962) distinguished two hydration processes in clay soils, namely, intercrystalline and intracrystalline swelling. Intercrystalline swelling takes place when the uptake of moisture is restricted to the external crystal surfaces and void spaces between crystals. Such swelling may occur in all materials but it is most significant in fine grained ones, particularly clays. In relatively dry clays the particles are held together by relict water under tension from capillary forces. On wetting these forces are relaxed and the material expands. Such swelling occurs in any type of clay, irrespective of mineralogical composition, although
        the amount of swelling depends on a number of factors including mineral species and the type and concentration of cations present in the porewater.”

        Intracrystalline swelling is a property of expansive soils in which saturation increases the depth of water absorbed between and around particles. It can be important in some regions.

        The soil matrix is known as the skeleton. And in increase in pore water pressure will cause the bones to expand and the time it takes depends on the head and pore size and connectivity.

      • Almost every major river delta region is eroding away and CO2 has nothing to do with it.
        “Scientists have discovered that the seafloor from the Mississippi River Delta to the Gulf of Mexico is eroding like the land loss that is occurring on the Louisiana coast.”
        “The scientists used historic nautical charts, data from academic research and the oil and gas industry as well as National Oceanic and Atmospheric Administration underwater mapping data collected from 1764 to 2009…
        Given the similarities between the Mississippi River Delta and river systems worldwide, we expect other major delta systems are entering decline. This has implications for delta ecosystems and biological, geological and chemical processes worldwide.”

        Don’t worry about sea levels when the bigger problem will be algae, anoxia and chemical/plastic pollution.

      • Robert

        Thanks for the information


  29. dennisambler

    “rather you might avoid building new major infrastructure (e.g. an airport) in coastal areas that could be impacted by such a worst-case sea level rise.”

    As with the Maldives?

    “The AR5 then makes the following projection, based on expert judgment:”

    In 1999, there was a series of seminars in Europe focusing on “Uncertainty in Climate Models”, known as the ECLAT series, “Representing Uncertainty in Climate Change Scenarios and Impact Studies” published by the Climatic Research Unit, University of East Anglia.

    “Projecting the future state(s) of the world with respect to demographic, economic, social, and technological developments at a time scale consistent with climate change projections is a daunting task, some even consider as straightforward impossible.

    Over a century time scale, current states and trends simply cannot be extrapolated. The only certainty is that the future will not be just more of the same of today, but will entail numerous surprises, novelties and discontinuities.

    “The probability of occurrence of long-term trends is inversely proportional to the ‘expert’ consensus.”

  30. In a Los Angeles Times editorial published in Sunday’s paper, editorial writer Scott Martelle writing about the paper’s demand that Scott Pruitt be fired because he doesn’t understand science, claims that, “As many as 20 million Americans could become climate refugees by the end of the decade,” mainly because of sea level rise. That’s roughly one year and 9 months away.

    He references a July 2015 study published in the Proceedings of the National Academy of Science, but it’s actually talking about over a long term – like 2,000 years . . their worst case scenario if a number of things occur – inc the complete collapse of WAIS. So far they are standing their ground – and have refused to issue a correction.

    How strong must a newspaper’s [4th largest circulation in US] hatred be to act out in such an unprofessional manner?

    • Today I read a 2016 report by the European Environmental Agency discussing Greenland losing its ice. It spoke of tens of millennia. That, is a very long time.

      The MSM never talk about any of these catastrophic predictions in such terms. I used to think it was out of ignorance. Not so anymore.

  31. Judith,

    Thanks for this interesting post. Just to provide some perspective on the policy relevance of projected sea level rise from 2000 to 2100, the economic impact is trivially small.

    FUND3.9 projects the global economic impact of sea level rise from 2000 to 2100, for ECS=3.0C and all other inputs as per IPCC AR5, is 0.1% of GDP.

    Sea level rise is effectively irrelevant for rational policy analysis.

  32. That should be -0.1% of global GDP

  33. Vertical land motion controls regional sea level rise patterns on the United States east coast since 1900

    Understanding observed spatial variations in centennial relative sea level trends on the United States east coast has important scientific and societal applications. Past studies based on models and proxies variously suggest roles for crustal displacement, ocean dynamics, and melting of the Greenland ice sheet. Here we perform joint Bayesian inference on regional relative sea level, vertical land motion, and absolute sea level fields based on tide gauge records and GPS data. Posterior solutions show that regional vertical land motion explains most (80% median estimate) of the spatial variance in the large-scale relative sea level trend field on the east coast over 1900-2016. The posterior estimate for coastal absolute sea level rise is remarkably spatially uniform compared to previous studies, with a spatial average of 1.4-2.3 mm/yr (95% credible interval). Results corroborate glacial isostatic adjustment models and reveal that meaningful long-period, large-scale vertical velocity signals can be extracted from short GPS records.

  34. Could there be an El Niño by December? Depends, but the thing one finds in a hurricane forecast.

  35. Here in the Netherlands we were scared by Stefan Rahmstorf who threatened that the West Antarctic Ice Sheet would completely slide into the ocean by the end of the century.

  36. nobodysknowledge

    Thank you for balanced and enlighteing posts JC. I think you have to decompose the sea level rise into the sea level budget components to say something meaningful of projections. In addition it will be important to have a clear definiton of sea level rise. Perhaps is the term geosentric sea level rise the best term to use, as different from relative sea level rise and from MSL or GMSL trend (which I call Fake Sea Level Rise as GIA is added).
    This is the differenciation of Fredriksee et al, 2017.”Sea level changes are generally expressed in two distinct reference frames: either relative to the local oceanfloor (relative sea level change) or relative to the Earth’s center of mass (geocentric or absolute sea levelchange). Global mean sea level (GMSL) changes due to mass redistribution are called barystatic changes.These barystatic changes are defined as the total volume change of the ocean, divided by the ocean surfacearea.”

    Another point: I think the collapse of western antarctic ice sheet from geothermic activity is rather unrealistic. Volcanic and other geothermic activity has only local impact when it happens in Iceland.

    • Adding GIA makes it less “fake”. That is why they add it. Fredrikse et al, 2017 is advocating also adding seafloor subsidence as it not being included in geocentric results in an underestimation of SLR acceleration, which is what policy makers need to know from sea level science: the complete picture.

      Now comes the advocating of hiding from the complete picture.

  37. We are still waiting for the dreaded accelleration in the Netherlands

    • Frederikse is from the Netherlands.

      A Consistent Sea-Level Reconstruction and Its Budget on Basin and Global Scales over 1958–2014 – Thomas Frederikse


      Different sea level reconstructions show a spread in sea level rise over the last six decades and it is not yet certain whether the sum of contributors explains the reconstructed rise. Possible causes for this spread are, among others, vertical land motion at tide-gauge locations and the sparse sampling of the spatially variable ocean. To assess these open questions, reconstructed sea level and the role of the contributors are investigated on a local, basin, and global scale. High-latitude seas are excluded. Tide-gauge records are combined with observations of vertical land motion, independent estimates of ice-mass loss, terrestrial water storage, and barotropic atmospheric forcing in a self-consistent framework to reconstruct sea level changes on basin and global scales, which are compared to the estimated sum of contributing processes. For the first time, it is shown that for most basins the reconstructed sea level trend and acceleration can be explained by the sum of contributors, as well as a large part of the decadal variability. The sparsely sampled South Atlantic Ocean forms an exception. The global-mean sea level reconstruction shows a trend of 1.5 ± 0.2 mm yr−1 over 1958–2014 (1σ), compared to 1.3 ± 0.1 mm yr−1 for the sum of contributors. Over the same period, the reconstruction shows a positive acceleration of 0.07 ± 0.02 mm yr−2, which is also in agreement with the sum of contributors, which shows an acceleration of 0.07 ± 0.01 mm yr−2. Since 1993, both reconstructed sea level and the sum of contributors show good agreement with altimetry estimates.

  38. The accelleration is in the models not in the observations.

    • For one, he’s using the PSMSL tide-gauge data. Skeptic-approved Holgate observation data. So right off the bat, you’re wrong.

      • jch

        I seem to remember that when I posted data from Holgate- derived from email conversations with him- you expressed scepticism about his knowledge on the subject of sea level change.

        So now you approve of him?


      • Well, as I understand it, he has improved the PSMSL dataset, and in doing so has rendered some of his earlier work to no longer be correct.

  39. A general question to anyone

    Of the four serious winter storms we have had here causing damage to sea walls and the railway line on top of the sea wall, all occurred at the peak of high tide. 1 of them a ‘normal’ high tide and three at a ‘super tide’;

    Is there any known connection to peak storm and peak high tide?

    If any of the storms had occurred a few hours earlier or later there would have been little damage.

    (high tides here range up to around 5.20m and a low tide is typically half a metre, so up to 5 metres difference.)


  40. Don Monfort,
    “whereas the projections out to 2100 using climate models that do not include the lower values of climate sensitivity would not produce warming substantially smaller than the climate model values.”

    Better on some regards. It’s missing a critical piece of information in the last 3 words.
    It seems the sentence compares two sets of climate model outputs.
    But what climate models produce the “values” referred to in the phrase “climate model values”.

    If I understand this correctly climate models that do not include the lower values of climate sensitivity would produce/predict more warming than models based on lower values of climate sensitivity. Yes?
    Thus the subset of models based on higher climate sensitivity values would be expected to “produce more warming” (but perhaps not substantially larger) than a general ensemble of climate models that use a mix of climate sensitivities (higher and lower). Yes?

    I had assumed that a climate model only uses one climate sensitivity value at a time. Does the phrase “include the lower values of climate sensitivity” mean a ensemble of climate model runs each using a different value for climate sensitivity? That is, same model varying only the climate sensitivity value.

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  43. (Coming in late) “The ‘likely range’ is consistent with the terms used by the IPCC meaning that it has about a 2-in-3 chance of containing the correct value.” As I’ve said before, in economic models, anything without a 95% probability would be rejected. 98% probability would be regarded as likely representing the true situation. In comparing the possible outcomes of alternative policies, impacts beyond ten years would generally be disregarded due to uncertainty and because of the discount rates used. As for 100 years hence – well, who would be stupid enough to try to project that far in our highly uncertain and always changing world?

    In my experience as a government economic policy adviser, no one would dream of putting forward a proposal on the basis of a two-in-three probability. That’s almost in the range of tossing a coin. Skip the fancy models and flip a coin.

  44. An informal and intuitive approach to SLR and its acceleration:

    1) SLR is currently rising at a rate of 1 inch/decade. The average rate of SLR was about 3/4 inch/decade. Not much has changed.

    2) If SLR accelerated at 1 inch/decade/decade, total SLR would be 37-45 inches after 8-9 decades. We clearly haven’t been experiencing the acceleration needed to reach the most alarming levels of SLR (1 m or more)
    in the past few decades.

    3) By the end of the century, an acceleration of 1 inch/decade/decade would produce about 8 inches of linear sea level rise and 4X as much (32 inches) of accelerated rise.

    4) Why can’t we wait until SLR has accelerated to at least 2 inches/decade before considering extreme scenarios. If alarming levels of acceleration do develop, we will have more than half a century to prepare (or mitigate through geo-engineering and possibly emissions reductions.)

    5) After repeated re-analysis of the earliest satellite altimetry data, Nerem (2018) reported statistically significant acceleration of SLR: 0.084 +/- 0.025 mm/yr/yr. That is 1/3 of an inch/decade/decade. That would produce about 12 inches of accelerated SLR and 20 inches overall. That is right in the middle of the IPCC’s central estimate for RCP6.0 for the end of the century,

    6) There are about 3 decades to 2050, with 1/3, 2/3, and 3/3 inches of additional SLR – 2 inches on top of a linear rise amounting to 3 inches.

    IMO, a good chunk of the GIS may be already doomed. However doom isn’t on track to arrive this century.

    • 1900 to 1990 – 1.2 mm/yr
      1993 – ~2.0 mm/yr: +1.67% in ~93 years
      1993 to present – 3.3 mm/yr: +1.65% in ~25 years
      last 10 years – 4.29 mm/yr: +1.3% in ~10 years
      last 5 years – 4.73 mm/yr: +1.1% in ~5 years

      There is no track. To date, since 1900, there has not been a dynamic collapse of an ice sheet. It’s a nonlinear system.

      But by all means, pray for the negative phase of the AMO.

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  47. The up/down/”back” radiation greenhouse gas energy loop of the radiative greenhouse effect theory is pencil on paper, a spreadsheet cell, a “what if” scenario and NOT a physical reality.

    Without this GHG energy loop, radiative greenhouse theory collapses.

    Without RGHE theory, man-caused climate change does not exist.

    And with a snap of the fingers and “Presto!!” the bazillion dollar global climate change fantasy is suddenly unemployed.

    Must be why nobody wants to talk about this possibility, not newsworthy enough.

  48. Pingback: TOP 10 Climate Change Alarmist Myths Unearthed : # 2 SEA LEVEL RISE | Climatism