IPCC Report to be Closely Watched on Climate Sensitivity, Sea-Level Rise

Part of the much-anticipated IPCC Fifth Assessment Report are to be officially released in late September, with much interest certain to focus on the approach to climate sensitivity and projected sea-level rise increases.

With the first official release of the IPCC Fifth Assessment Report expected on Friday, September 27, print and broadcast media across the U.S. have begun reporting on widely available working drafts of the Working Group I report, evaluating the scientific literature on the physical science behind climate change.

Initial reports on the draft indicate increasing confidence behind the underlying science and behind a substantial human role in warming, primarily as a result of burning fossil fuels. That’s unlikely to come as a surprise to many who have regularly reviewed the peer-reviewed literature on the issue over recent years.

Using its established metrics for showing degrees of confidence, it appears the final report will increase the level of confidence concerning a human impact from 90 percent to 95 percent. The IPCC report at this point is likely also to reflect a downward revision in climate sensitivity but heightened concerns about risks of greater sea-level rise and threats to coastal communities.

New York Times reporter Justin Gillis’s August 19 front-page piece on a leaked version of the draft report noted continued difficulties in making reliable forecasts of likely climate change impacts at the local level, leaving governments and businesses “fumbling in the dark as they try to plan ahead.”

On the closely-watched issue of whether the global climate may be less sensitive to a doubling of carbon dioxide concentrations than earlier projected, Gillis wrote that the new draft “says the rise could be as low as 2.7 degrees F,” as opposed to the low-end projection of 3.6 degrees F in the 2007 Fourth Assessment Report. “But the draft says only that the low number is possible, not that it is likely,” Gillis reported, adding: “Many climate scientists see only a remote chance that the warming will be that low, with the published evidence suggesting that an increase above 5 degrees F is more likely if carbon dioxide doubles.”

Another issue certain to draw close attention in the new report will involve treatment of sea-level rise, in part because many believe sea-level rise projections in the previous assessment report had been overly conservative. Under the “most optimistic” scenario, Gillis reported, the draft projects that sea level could rise by only about 10 inches by 2100. But “at the other extreme,” with emissions continuing to swiftly increase, “sea-level rise could be expected to rise at least 21 inches and might increase a bit more than three feet” by the end of this century. A three-foot rise “would endanger many of the world’s great cities — among them New York, London, Shanghai, Venice, Sydney, Australia, Miami, and New Orleans,” he wrote.

Under current IPCC planning, the individual working groups are expected to release their reports starting at 10 a.m. Swedish time, 4 a.m. EDT, on Friday, September 27, after Working Group I meets over the preceding four days to review and approve its report. Working Group II, which is assessing scientific literature on impacts, adaptation, and vulnerability, is currently scheduled to meet to approve its report March 25-29, 2014, with release of that report expected soon thereafter. Working Group III, which is assessing scientific literature on mitigation, is scheduled to meet April 7-11, 2014, with the release of that report again expected soon after that meeting ends.

The all-important “Synthesis Report,” which many think is the only part of the full report many close observers and policy experts might actually be tempted to read in full, is unlikely to be officially released before authors meet October 27-31, 2014.

It’s highly likely that advance leaks of information from drafts of each of the working groups will continue right up to the times IPCC officially releases them, with IPCC continuing to remain officially mum until each is actually released.

Those interests traditionally labeled as being “skeptics” of the IPCC and its findings are expected to try to make the climate sensitivity and related warming “pause” issues the prisms through which the public will view the full body of work. Proponents of aggressively reducing carbon dioxide emissions, on the other hand, are certain to seek to counter those arguments and maintain that even the lower climate sensitivity figures continue to pose major challenges and do little more than buy additional time for serious mitigation. They are expected also to attempt to marshal increased public concern surrounding the sea-level rise issue and prospects for more severe weather anomalies and storm surges and increasing risks to public health and infrastructure resources.

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