Extreme Misrepresentation: USGCRP and the Case of Floods

The US Global Change Research Program has released a draft national assessment on climate change (here in PDF) and its impacts in the United States, as required by The US Global Change Research Act of 1990 (which incidentally was the subject of my 1994 PhD dissertation). There has been much excitement and froth in the media.

Here I explain that in an area where I have expertise on, extremes and their impacts, the report is well out of step with the scientific literature, including the very literature it cites and conclusions of the IPCC. Questions should (but probably won't) be asked about how a major scientific assessment has apparently became captured as a tool of advocacy via misrepresentation of the scientific literature -- a phenomena tha occurs repeated in the area of extreme events. Yes, it is a draft and could be corrected, but a four-year effort by the nation’s top scientists should be expected to produce a public draft report of much higher quality than this.

Since these are strong allegations, let me illustrate my concerns with a specific example from the draft report, and here I will focus on the example of floods, but the problems in the report are more systemic than just this one case.

What the USGCRP report says:

Infrastructure across the U.S. is being adversely affected by phenomena associated with climate change, including sea level rise, storm surge, heavy downpours, and extreme heat… Floods along the nation’s rivers, inside cities, and on lakes following heavy downpours, prolonged rains, and rapid melting of snowpack are damaging infrastructure in towns and cities, farmlands, and a variety of other places across the nation.

The report clearly associates damage from floods with climate change driven by human activities. This is how the draft was read and amplified by The New York Times:

[T]he document minces no words.

“Climate change is already affecting the American people,” declares the opening paragraph of the report, issued under the auspices of the Global Change Research Program, which coordinates federally sponsored climate research. “Certain types of weather events have become more frequent and/or intense, including heat waves, heavy downpours, and, in some regions, floods and droughts."

To underscore its conclusion, the draft report includes the figure at the top of this post (from Hirsch and Ryberg 2011), which shows flood trends in different regions of the US. In a remarkable contrast to the draft USGCRP report, here is what Hirsch and Ryberg (2011) actually says:

The coterminous US is divided into four large regions and stationary bootstrapping is used to evaluate if the patterns of these statistical associations are significantly different from what would be expected under the null hypothesis that flood magnitudes are independent of GM [global mean] CO2. In none of the four regions defined in this study is there strong statistical evidence for flood magnitudes increasing with increasing GMCO2.

Got that? In no US region is there strong statistical evidence for flood magnitudes increasing with increasing CO2. This is precisely the opposite of the conclusion expressed in the draft report, which relies on Hirsch and Ryberg (2011) to express the opposite conclusion.

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