Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”
The UN’s Intergovernmental Panel on Climate Change (IPCC) is set to release its Fifth Assessment Report (AR5) of the physical science of climate change at the conclusion on its editorial meeting in Stockholm scheduled from September 23-26th.
A version of its Summary for Policymakers (SPM)—perhaps the most influential portion of the report as it is the widest read—has been “leaked” to generate media interest in the upcoming release. It certainly has, but perhaps not in the manner intended. The leaked SPM has revealed a document so flawed and removed from current science that it has been described as not only being “obsolete on the day that it is released, but that it will be dead wrong as well” (okay, we wrote that).
In the Summary for Policymakers section of its Fourth Assessment Report (published in 2007) the IPCC had this to say about the rate of sea level rise:
Global average sea level rose at an average rate of 1.8 [1.3 to 2.3] mm per year over 1961-2003. The rate was faster over 1993 to 2003: about 3.1 [2.4 to 3.8] mm per year. Whether the faster rate for 1993 to 2003 reflects decadal variability or an increase in the longer-term trend is unclear.
Since then, we have highlighted numerous findings in the scientific literature that present strong evidence that the increase in the rate of sea level rise since 1993 is largely not an increase in the longer-term trend (or at least not from human-caused climate change which is the IPCC’s implication) and that the short-term rate of sea level rise has been slowing, and returning back towards the long-term average.
But the IPCC’s heart remains hardened.
The leaked version of the AR5 SPM includes this description of sea level rise:
It is very likely that the mean rate of global averaged sea level rise was 1.7 [1.5 to 1.9] mm yr–1 between 1901 and 2010 and 3.2 [2.8 to 3.6] mm yr–1 between 1993 and 2010. Tide-gauge and satellite altimeter data are consistent regarding the higher rate of the latter period. It is likely that similarly high rates occurred between 1920 and 1950.
Notice that they dropped any statement wondering whether the recent rate of rise was an increase in the longer-term trend or the result of short-term variability or other non- climate-change-related factors—even though the difference between these cases has implications for our understanding of sea level rise and how it may evolve into the future.
We repeat—recent scientific findings argue that rate of sea level rise since 1993 is little different than the long-term (20th century) rate of sea level rise once natural variability and non-climatic influences are accounted for.
Here are two papers demonstrating this fact.
The first was published by a research team led by Yoshide Wada and which we covered last summer. Wada and colleagues examined how much of an influence human pumping of groundwater for irrigation etc.—water which eventually finds its way into the global oceans—was having on the sea level. They found the impact to be quite significant, concluding:
[O]ur results compare well with independent estimates for the present groundwater depletion rates… and show that groundwater depletion is likely to be the major component of terrestrial contribution to sea-level change in the coming decades.
The data that they compiled on ground water depletion and surface impoundments (dams) show that for the period from 1993-2011, the net contribution (termed “dewatering” of the continents) has resulted in a sea level rise of about 0.44 mm/yr (+/- 0.1mm/yr)—and they predict this rate to increase by mid-century.
This 0.44 mm/yr (of the observed 3.2 mm/yr) of sea level rise since 1993 is not related to anthropogenic climate change as a result of greenhouse gas emissions.
A second relevant paper was published a few weeks ago. In this one, a team led by University of Colorado’s Ben Hamlington examined how large an influence multi-decadal natural oscillations of an important Pacific Ocean climate state—called the Pacific Decadal Oscillation (PDO)—has on global sea level. Since the PDO oscillation is pretty slow, approximately 60 years or so, the researchers note that it is “difficult to assess the contribution of decadal to multi-decadal climate signals to the global trend” using a record that only begins in 1993. By attempting to identify the influence of the PDO, Hamlington and colleagues could then estimate the PDO’s effect on the global mean sea level (GMSL) trend. They write:
We estimate the PDO contribution to the GMSL trend over the past twenty years to be approximately 0.49 ± 0.25 mm/year, and find that removing the PDO contribution reduces the acceleration in GMSL estimated over the past sixty years.
As the PDO is a natural phenomenon, that’s another 0.49 mm/yr (of the 3.2 mm/yr since 1993) not caused by anthropogenic greenhouse gas emissions.
A quick review of the math shows us that of the IPCC’s 3.2 mm/yr of sea level rise from 1993 only 2.27 mm/yr is left after accounting for natural oscillations in the Pacific and the “dewatering” of the continents.
Color us jaded, but 2.27 mm/yr doesn’t sound all that much different from the long-term 1.7 mm/yr, especially when the confidence intervals of the calculations are all included.
In other words, had the IPCC accurately reported the extant science on the factors behind the reported increase in the rate of sea level rise since 1993, the reader of the SPM would have been left with a much different impression of its evolution—one which the current situation is not that much different from the past (and to which we have largely adapted), instead of one in which the reader is left to think that anthropogenic climate change has resulted in a near doubling of the long-term rate of sea level rise.
Isn’t the IPCC supposed to be giving the best scientific explanation of what it taking place, not one which is colored by trying to support a fracturing consensus?
We think it is high time for the IPCC to end its charade (and save the global tax-payer huge sums of money in the process).
Hamlington, B.D.„ et al., 2013. Contribution of the Pacific Decadal Oscialltion to Global mean Sea Level. Geophysical Research Letters, doi: 10.1002/grl.50950.
Wada, Y., et al., 2012. Past and future contribution of global groundwater depletion to sea-level rise. Geophysical Research Letters, doi: 10.1029/2012GL051230