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.”
Let us see if we can help New York Times’ global warming reporter Justin Gillis out.
In his article yesterday about the upcoming Fifth Assessment Report of the U.N.’s Intergovernmental Panel on Climate Change (IPCC), Gillis laments that the IPCC seems to be tamping down some of the more alarmist scenarios when it comes to the projected rate of rise of global temperatures and sea level.
Concerning projections of sea level rise, Gillis bemoans that the IPCC looks like (the final version of the Summary for Policymakers of the new report isn’t scheduled for release until the end of the this month at the conclusion of an IPCC editorial meeting in Stockholm) it will discount the “outlier” estimates that the rise this century will exceed five feet. Gillis writes “The drafters of the report went with the lower numbers, choosing to treat the outlier science as not very credible.”
When it comes to how fast the global average temperature is projected to rise, Gillis rues the possibility that the IPCC will lower its assessed value of the climate sensitivity, writing “In this case, the drafters of the report lowered the bottom end in a range of temperatures for how much the earth could warm, treating the outlier science as credible.”
Gillis can’t wait for the explanation:
…[I]t would be nice to hear an explanation from the drafters of this coming report as to why they made decisions that effectively play up the low-end possibilities. But with the report still officially under wraps, they are not speaking publicly. We are thus left wondering whether it is a matter of pure professional judgment — or whether they have been cowed by the attacks of recent years.
Assuming these decisions withstand final review, it will be fascinating to hear the detailed explanations in Stockholm.
We’ll end the suspense for him.
The reason that the IPCC should discount the possibility that the sea level will rise more than three feet by the year 2100 is that such a possibility has largely been discredited in the scientific literature and well as simply by looking out the window (i.e., the observed rate of sea level rise is only about 1.25 inches per decade and there is A LOT of ice in Greenland and Antarctica that is not going anywhere fast).
And the reason that the IPCC should lower its estimates of the earth’s climate sensitivity (i.e., how much the earth’s average temperature rises as a result of a doubling of the atmospheric concentration of carbon dioxide) is that the overwhelming majority of the recent findings in the scientific literature show that the most likely value is far beneath what it was assessed at in previous IPCC reports. In fact, the new equilibrium climate sensitivity estimates are so low as to put the IPCC in a quandary—if they were to fully embrace the new findings, they would have to discredit all the future climate projections made in the new report as they were generated by climate models with and average climate sensitivity that is nearly 75 percent higher than the new findings suggest. So if anything, the IPCC will likely be too conservative in lowering its assessment of the climate sensitivity in the final version of its Fifth Assessment Report.
So, pure and simple, the reason that the IPCC should embrace estimates of a slower global temperature increase and a lower global sea level rise is because that is what the current science supports.
Gillis could have saved himself a lot of wondering (and ink) had he only been reading these pages!