Rupert Darwall writes in the WSJ:
“Human influence extremely likely to be the dominant cause of observed warming since the middle of the last century,” was the headline from Friday’s release of the first instalment of the Intergovernmental Panel on Climate Change’s fifth assessment report. “Extremely likely”—indicating a 95%-100% likelihood—was ratcheted up one notch from the 2007 fourth assessment report’s “very likely.” Yet compared to 2007, the IPCC widened its estimate of the responsiveness of the climate system to carbon dioxide by reducing the lower band to a 1.5°C increase from 2°C, qualifying the new estimate as only “likely.”
This is a glaring discrepancy. How can the IPCC be more confident that more than half the temperature rise since the mid-20th century is caused by greenhouse-gas emissions when it is less sure of the climatic impact of carbon dioxide? The explanation is that IPCC reports, especially the summaries for policymakers, are primarily designed for political consumption. And as if on cue, British Prime Minister David Cameron commented on the IPCC report, “If someone said there is a 95% chance that your house might burn down, even if you are in the 5% that doesn’t agree with it, you still take out the insurance”…
Politicization is thus an ingrained feature of IPCC reports. After the fiasco of the 2007 assessment, the U.N. secretary general asked the InterAcademy Council to review IPCC processes and practices. The committee, chaired by Princeton economist Harold Shapiro, observed that government representatives and scientists meet to agree the final wording of the summary for policymakers line by line “for clarity of message” and to get government “buy-in.” Perhaps that’s being polite. The real question is who is buying whom.
The committee recommended changes in IPCC governance, which were mostly ignored, and specifically recommended that the IPCC not use the quantitative probability scale that it re-used last week, as in the IPCC’s 95% probability headline. The body’s flagrant disregard for the InterAcademy Council’s findings and its reluctance to address the 15-year warming pause are symptomatic of a failure of leadership. The conclusion is unavoidable: The IPCC is unreformable and the Fifth Assessment Report should be the IPCC’s last.