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When can we expect extremely high surface temperatures?

Sure glacier melt, sea level rise, extreme drought, and species loss get all the media attention — they are the Britney Spears, Paris Hilton, and Barack Obama of climate impacts. But what about good old-fashioned sweltering heat? How bad will that be? Two little-noticed studies — one new, one old — spell out the grim news.

Bottom line: By century’s end, extreme temperatures of up to 122°F would threaten most of the central, southern, and western U.S. Even worse, Houston and Washington, DC could experience temperatures exceeding 98°F for some 60 days a year.

The peak temperature analysis comes from a Geophysical Research Letters paper published two weeks ago that focused on the annual-maximum “once-in-a-century” temperature. Researchers looked at the case of a (mere) 700 ppm atmospheric concentrations of CO2, the A1b scenario, with total warming of about 3.5°C by century’s end. The key scientific point is that “the extremes rise faster than the means in a warming climate.”

The results, depicted above (in °C), are quite remarkable, especially when you consider that, instead of 700 ppm, we could easily end up closer to 1000 ppm by century’s end (see here), in which case these record temperatures could be seen closer to 2060 than 2100:

… values in excess of 50°C [122°F] in Australia, India, the Middle East, North Africa, the Sahel and equatorial and subtropical South America.

As you can see from the map, extreme temperature peaks are only slightly lower over large parts of this country. The study notes:

Such temperatures, if lasting for some days, are life threatening and receive relatively little attention in the climate change debate.

So now the question is, has anybody done an analysis of what global warming could do to intense heat waves that last very long times, weeks or months? The answer is yes, and the results of that study are more worrisome — and it also received relatively little attention.

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The November 2005 study in the Proceedings of the National Academy of Sciences, “Fine-scale processes regulate the response of extreme events to global climate change,” found that “peak increases in extreme hot events are amplified by surface moisture feedbacks.” The study looked at the A2 scenario (about 850 ppm in 2100) in the second half of this century (from 2071 to 2095). It examined temperature rise projections, plus “fine-scale processes,” such as how local warming is affected by loss of snow cover and loss of soil moisture. I interviewed the lead author, Noah Diffenbaugh, of Purdue University, for my book.

Houston and Washington, DC would experience temperatures exceeding 98°F for some 60 days a year. Oklahoma would see temperatures above 110°F some 60 to 80 days a year. Much of Arizona would be subjected to temperatures of 105°F or more for 98 days out of the year — 14 full weeks. We won’t call these heat waves anymore. As Diffenbaugh told me, “We will call them normal summers.”

And again, that’s not even the worst case, since it’s “only” based on 850 ppm.

The time to act is yesterday.