A US science advisory committee released a draft climate assessment for public review today, documenting a range of global-warming impacts across the United States and declaring that more trouble is on the way in the coming decades.
Produced under the auspices of the interagency Global Change Research Program, the draft document will serve as the basis for the United States’ third national climate assessment, scheduled for release later this year or in early 2014. The previous assessments were released in 2000 and 2009.
Coming just days after news that the United States experienced its hottest year on record in 2012, the draft report says that average US temperatures have increased by more than 0.8° Celsius since 1895, with a sharp spike since 1980. It also provides an update on the litany of impacts being analysed by scientists. There is “strong evidence” that global warming has roughly doubled the likelihood of extreme heat events, contributing to droughts and wildfires, according to the report. Permafrost is melting in Alaska, and much of the country is experiencing more extreme rainfall and winter snowstorms.
“Climate change, once considered an issue for a distant future, has moved firmly into the present,” leaders of the National Climate Assessment and Development Advisory Committee said in a letter accompanying the document. Environmentalists immediately said the report underscores the need for action, but it will also attract scrutiny from sceptics in the days ahead.
Looking forward, the assessment centres on impacts that can be expected under a pair of emissions scenarios for the twenty-first century, assuming both high and low levels of greenhouse-gas emissions. Under these scenarios, which were among those used by the Intergovernmental Panel on Climate Change (IPCC) in its fourth assessment in 2007, average temperatures across the United States could rise by roughly 1.7–5.6° C by the end of the century. (The actual increase will depend on global emissions going forward, however, and so far the world is tracking above even the high-emissions scenario.) Individual chapters focus on everything from forestry and water resources to public health. The advisory committee also provided independent assessments for different regions of the country and sectors of the economy while documenting efforts to reduce emissions and prepare for the coming changes.
Akin to the IPCC assessments, the document does not present new evidence but instead assembles and assesses scientific studies that were published or in press as of 31 July 2012. More than 240 academics, consultants, business representatives and other experts took part in the draft released today; the document will be available for public comment between 14 January and 12 April.