The U.S. Climate Change Science Program (a.k.a. the Bush Administration) has issued a must-read report, Weather and Climate Extremes in a Changing Climate. It wouldn’t be must-read or even big news if it weren’t for the fact that

  • Many environmentalists stopped talking about the extreme weather/global warming link a decade ago.
  • The deniers, the delayers, and of course the Roger Pielkes of the world have pushed back against any claims that climate change is driving the extreme weather we see today. (as Chico Marx (dressed as Groucho) said “Who you gonna believe, me or your own eyes?“)
  • The media has been brow-beaten by the deniers into downplaying the connection. The journalist Ross Gelbspan has a long discussion of this in his great 2004 book, Boiling Point — I will blog on this later.
  • The Midwest is experiencing the second “500-year flood” in 13 years. (Don’t worry, big media, it’s all just a big coincidence like the deniers keep saying.)

This report is really an “I told you so” from NOAA’s National Climatic Data Center and Tom Karl in particular, who has been a real leader in this area, helping to create the still rarely-discussed Climate Extremes Index (see “Still, waters run deep“).

If you don’t read the whole report, at least read the synopsis:

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Changes in extreme weather and climate events have significant impacts and are among the most serious challenges to society in coping with a changing climate.

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Many extremes and their associated impacts are now changing. For example, in recent decades most of North America has been experiencing more unusually hot days and nights, fewer unusually cold days and nights, and fewer frost days. Heavy downpours have become more frequent and intense. Droughts are becoming more severe in some regions, though there are no clear trends for North America as a whole. The power and frequency of Atlantic hurricanes have increased substantially in recent decades, though North American mainland land-falling hurricanes do not appear to have increased over the past century. Outside the tropics, storm tracks are shifting northward and the strongest storms are becoming even stronger.

It is well established through formal attribution studies that the global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases. Such studies have only recently been used to determine the causes of some changes in extremes at the scale of a continent. Certain aspects of observed increases in temperature extremes have been linked to human influences. The increase in heavy precipitation events is associated with an increase in water vapor, and the latter has been attributed to human-induced warming. No formal attribution studies for changes in drought severity in North America have been attempted. There is evidence suggesting a human contribution to recent changes in hurricane activity as well as in storms outside the tropics, though a confident assessment will require further study.

In the future, with continued global warming, heat waves and heavy downpours are very likely to further increase in frequency and intensity. Substantial areas of North America are likely to have more frequent droughts of greater severity. Hurricane wind speeds, rainfall intensity, and storm surge levels are likely to increase. The strongest cold season storms are likely to become more frequent, with stronger winds and more extreme wave heights.

Current and future impacts resulting from these changes depend not only on the changes in extremes, but also on responses by human and natural systems.

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This post was created for, a project of the Center for American Progress Action Fund.