Scary but fake news about the National Climate Assessment

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by Fabius Maximus 

Summary: Volume II of the Fourth National Climate Assessment (NCA) has dominated the news in the weeks since its release. One of the major findings that journalists headlined was the effect of climate change on the US economy. Ten percent is vivid number to grab the attention of Americans still skeptical after thirty years of dire warnings about climate change. Unfortunately it is a dubious story, as explained in these tweets by Roger Pielke Jr. Posted with his permission.

CNN: Ten Percent hit to GDP from Climate Damage


“Here is the NYT front page on 24 November, with Coral Davenport’s NCA story in the top right. It set the subsequent narrative of the NCA around the 10% GDP number, perhaps the least supportable claim in the entire report. The 10% figure should not have been in the report. How did this science communication failure occur?”

NYT front page on 24 November 2018

“Davenport is an excellent journalist and did not invent the 10% GDP number. I suspect it was promoted to her by someone involved in the report, unnamed in NYT article. I see no evidence that the 10% number was part of U.S. Global Change Research Program’s (USGCRP) promotion of the report.

“Where did the number come from? See this from Chapter 29 of NCA (annotated, legend below).”

NCA - climage change effect on GDP

“{The} graph shows projections of direct damage to the current U.S. economy for six impact sectors (agriculture, crime, coasts, energy, heat mortality, and labor) as a function of global average temperature change (represented as average for 2080–2099 compared to 1980–2010). …Dot-whiskers indicate the uncertainty in direct damages in 2090 (average of 2080–2099) derived from multiple combinations of climate models and forcing scenarios (dot, median; thick line, inner 66% credible interval; thin line, inner 90%). The gray shaded area represents the 90% confidence interval in the fit (black line) to the damage estimates.”

“Where does that graphic come from? “Estimating economic damage from climate change in the United States” by Solomon Hsiang et al. in Science, 30 June 2017.” Same x-axis as in the NCA, but expressed in degrees C. Click to enlarge.

Hsiang - GDP Damage from Climate change

“But oddly, elsewhere the NCA associates RCP 8.5 with only a 4° C temp change. Even the 95th percentile is less than 5.5° C (10° F). See this graph from Chapter 2 of the NCA.”

NCA chapter 2 - graph of global temperature change per RCP

“So the headline, repeated everywhere 10% GDP number is not consistent with the physical science part of the report and represents a temperature change twice that of the already implausible RCP 8.5 scenario. …Shouldn’t such an outlandish, outlier conclusion been caught in the review process? Not a good look that sole review editor for this chapter is an alum of the Center for American Progress …. Even rudimentary attention to COI {conflict of interest?} would avoided this.”

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“Bottom line: If experts are going to demand that they be trusted, their numbers should add up right. They don’t here. One way to ensure robust assessments is to invite in critical voices, rather than exclude them. This error was easily preventable.

“Climate change is real, and aggressive mitigation and adaptation make very good sense. Trump is still wrong. Which makes an error of this magnitude so much the worse.”


“Such a major assessment needs to be water tight, not a vehicle for stealth advocacy. If I were a contributor to this report I’d be POed at how it has been spun.”

Also, “RCP 8.5 is problematic not because some use it as a ‘worst case’ scenario (reasonable people can disagree on that), but when it is used as a ‘business as usual’ (BAU) scenario, to predict future impacts and ground Community Based Adaptation (CBA). That is a misuse of the scenario. RCP 8.5 as a BAU is implausible, as per the IPCC.

“In the NCA, RCP 8.5 is presented both as an extreme scenario and as the business as usual scenario. This is sloppy, but also a “thumb on the scale” for expressing Integrated Assessment Model (IAM) results for future impacts and benefits of mitigation. That is a shame because justifications for climate policy do not need exaggeration.

“If justifications for climate policy depend upon any scenarios of economic impact to 2100, we are doing it wrong. Effective climate policy must be built upon policies that can be justified on political time scales, that add up to long-term progress.”

See his tweets at @RogerPielkeJr !


Editor’s afterward

The headline 10% hit to GDP relies on assumption of an 8°C increase from current temperatures. Pielke gives a mild rebuttal to this massive failure in the NCA’s review process. Worse, the NCA authors and mainstream climate scientists remained silent as journalists ran with this number, far beyond anything likely to happen. To mention just one factor, the tech advances required to mine so much fossil fuel (mostly coal) contradicts RCP8.5’s assumption of tech stagnation.

There is another oddity in the NCA. It says “RCP8.5 is generally associated with higher population growth, less technological innovation, and higher carbon intensity of the global energy mix. ….Current trends in annual greenhouse gas emissions, globally, are consistent with RCP8.5.” But the RCP Database shows that current emissions are also consistent with RCP 2.6, which is the best-case scenario used in the IPCC’s Fifth Assessment Report. The emissions trend (through 2016) lies between lines of the two scenarios.

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For more about this subject

Climate Change Policy: What Do the Models Tell Us?” by Robert S. Pindyck in Journal of Economic Literature, September 2013.

Also see Roger Pielke Jr.’s “Opening Up the Climate Policy Envelope” in Issues, Summer 2018.

“Using RCP 8.5 to project future climate impacts can help us understand a potential worst-case scenario, but using it as a generic business-as-usual scenario thus contributes to the toxic politics of climate policy.”

Roger Pielke Jr
Roger Pielke Jr.

About the author

Roger Pielke, Jr. is a Professor of Environmental Studies at the U of CO-Boulder. He was Director of the Center for Science and Technology Policy Research. He is now Director of the Sports Governance Center in the Dept of Athletics. Before joining the faculty of the U of CO, from 1993-2001 he was a Scientist at the National Center for Atmospheric Research.

His research focuses on science, innovation and politics. He holds degrees in mathematics, public policy and political science from the University of Colorado. In 2006 he received the Eduard Brückner Prize in Munich for outstanding achievement in interdisciplinary climate research. In 2012 Roger was awarded an honorary doctorate from Linköping University in Sweden and the Public Service Award of the Geological Society of America.

His page at the Center for Science and Technology Policy Research has his bio, CV, and links to some of his publications. His website has links to his works, and essays about the many subjects on which he works.

He is also author, co-author or co-editor of seven books, including The Honest Broker: Making Sense of Science in Policy and Politics (2007), The Climate Fix: What Scientists and Politicians Won’t Tell You About Global Warming (2010), The Edge: The War against Cheating and Corruption in the Cutthroat World of Elite Sports (2016), and his latest work (a revision of his 2014 book) – The Rightful Place of Science: Disasters & Climate Change (see below).

Some of his recent publications.


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