Earlier this summer we presented a summary series on the Clintel Report on the IPCC’s 6th Assessment Report. The report’s coauthor Marcel Crok also included a chapter tracing how scientific language that was more or less accurate in the body of the Working Group 1 (physical science) report got twisted in the Summary for Policymakers and then distorted out of recognition in the Working Group 2 (social impacts) report. It’s an important reminder that the IPCC isn’t one group, it’s many groups that increasingly don’t even talk to each other, and just because one group occasionally gets something right doesn’t mean the IPCC as a whole can be trusted.
The Working Group 1 report pointed out (p. 1569) that even though many places are seeing more precipitation, there is no evidence of a climate change-induced increase in flooding. They concluded that “In summary there is low confidence in the human influence on the changes in high river flows on the global scale.” But the “Summary for Policymakers” said the opposite, that “Human influence has likely increased the chance of compound extreme events... [including] compound flooding in some locations.”
Then in the Working Group 2 report they threw caution even further into the swollen river and said “Extreme weather events causing highly impactful floods and droughts have become more likely and (or) more severe due to anthropogenic climate change (high confidence).” So the opposite of what the data show and what the other part of the IPCC had concluded.
Regarding drought, in the Working Group 1 report the IPCC expanded its definition of drought to distinguish between streamflow deficits, precipitation deficits and deficient soil moisture. In all three cases they admit to low confidence in trends and in human influence, though they have slightly more confidence of a climate-induced trend in soil drying in some places. In the Summary for Policymakers, they only highlighted the latter point and made no mention of the lack of evidence for the other drought types.
Again, Working Group 2 then twisted the finding further, into “Anthropogenic climate change has contributed to the increased likelihood and severity of the impact of droughts (especially agricultural and hydrological droughts) in many regions (high confidence).” Again, conceal the uncertainties and exaggerate the confidence.
Regarding hurricanes the IPCC Working Group 1 said “There is low confidence in most reported long-term (multi-decadal to centennial) trends in Tropical Cyclone frequency- or intensity-based metrics due to changes in the technology used to collect the best-track data.” Crok points out that the phrasing includes a mild dig at the way the data are collected, but they were relying on the best available data which all the experts use. In the “Summary for Policymakers” they again ignored the overall lack of trend and instead highlight that there has been a slightly increasing tendency for hurricanes to become major over the past 40 years, without mentioning that the proportion has likely fallen in comparison to data even further back. Then the IPCC Working Group 2 twisted the findings yet again to say: “Some extreme weather events are increasing in frequency and (or) severity as a result of climate change... [including] more frequent and stronger cyclones/hurricanes and resulting extreme rainfall.” Which was the precise opposite of the Working Group 1 findings, and the opposite of the available data.
If ever you are challenged over whether you “believe” the IPCC experts, you better ask which experts in which Working Group. Because on a lot of important topics, they apparently don’t believe each other.
