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Who Can Understand This Climate Change Report?

A new analysis suggests IPCC summaries aimed specifically at policymakers are harder than ever to digest.
(Photo: Ingka D. Jiw/Shutterstock)

(Photo: Ingka D. Jiw/Shutterstock)

One of the central goals of the Intergovernmental Panel of Climate Change's periodic assessment reports is to communicate what scientists know about climate change in an understandable way. Despite that goal—and recent efforts to overhaul IPCC's communications strategy—the latest climate-science summaries are harder than ever to digest, according to a new analysis.

Climate science is complicated business, but policymakers need to comprehend it well enough to act on what scientists know. In recognition of those facts, IPCC has always included summaries meant to be readable by anyone with a serious interest in climate change. Often, however, the summaries fall short of that goal, threatening one of IPCC's most important aims. From the Fifth Assessment Report's Synthesis Report Summary for Policymakers (SPMs):

Emissions scenarios leading to CO2-equivalent concentrations in 2100 of about 450 ppm or lower are likely to maintain warming below 2°C over the 21st century relative to pre-industrial levels. These scenarios are characterized by 40 to 70% global anthropogenic [greenhouse gas] emissions reductions by 2050 compared to 2010, and emissions levels near zero or below in 2100.

It gets worse after that. To be fair, that passage was cherry-picked to emphasize how unreadable the SPMs can be. Wondering how difficult SPMs actually are on readers—and whether that's changed over time—KEDGE Business School associate professor Ralf Barkemeyer and his colleagues subjected SPMs and related news reports to the Flesch Reading Ease algorithm, a 100-point scale that takes into account just two factors: average sentence length and the average number of syllables per word.

IPCC summaries do not fare well on readability. Averaging the 20 SPMs in IPCC’s five assessment reports, they score just 20 points. In contrast, quality newspaper reports score around 40 points, while tabloid newspapers reach around 50 points. The summary of IPCC's report on climate-change mitigation strategies was especially bad, scoring just 6.7 points on the readability scale. (This article scores about 39 points, not counting the quoted section above.)

What's more, there are hints that the summaries’ readability is sinking. The first summaries issued in 1990 scored an average of 25.9 points, while the latest round from the 2014 Fifth Assessment Report scored 14 points on average. The trend is more complicated than that. After dropping to 17.5 points in the second round of SPMs, scores actually increased to 21.1 in the Fourth Assessment Report, but even so the numbers do not bode well for IPCC's mission of communicating climate science.

"The IPCC needs to find ways to improve the readability of its SPMs," perhaps by engaging professional science communicators in the process. That, or face the prospect that policymakers and the public will no longer understand what's happening to the climate, the team writes today in Nature Climate Change.

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