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Extreme Weather Events Linked To Climate Change

Research shows that some episodes of extreme heat and/or drought linked to human-induced global warming

by Rudy M. Baum
July 30, 2012 | A version of this story appeared in Volume 90, Issue 31

The head and deck of a front-page story in the July 17 Washington Post read:

Drought is worst in half a century
Forecasters say relief is unlikely to come soon

The story states, “About 55 percent of the continental United States is now designated as in moderate drought or worse, the largest percentage since December 1956, according to the National Climatic Data Center, and the outlook is grim.”

There have been a lot of headlines and stories like that from around the world in recent years. The ferocious derecho that ripped across the Midwest and Middle Atlantic in late June was unprecedented. In the summer of 2011, much of Texas baked under extreme heat and drought. The heat wave in Russia in 2010 that killed 11,000 people in Moscow alone “was the most extreme heat wave in the instrumental record of 1880–present for that region,” according to the National Oceanic & Atmospheric Administration (NOAA).

In a speech during the Kavli celebration in Oslo, Norway, in 2010, U.S. presidential science adviser John P. Holdren made an interesting point. He said: “Global warming is a dangerous misnomer. It suggests that the changes are uniform, primarily about temperature, gradual, and likely benign. None of these are true.” The phenomenon, Holdren said, should be called “global climate disruption.”

I think of Holdren’s words when I read stories like the ones I’ve cited above. I particularly thought of his words last week, when the temperature in Washington, D.C., bumped up against 100 °F for a number of days for the second time this summer. This is what a disrupted climate looks like, I said to myself.

Until recently, lots of climate scientists, meteorologists, and climate-change skeptics would have taken issue with those thoughts. “You cannot link an individual extreme weather event to anthropogenic climate change,” they would intone sternly. Doesn’t matter that the extreme events we’re experiencing are the very ones that climate-change models predict will happen. Connection denied!

Until now. Earlier this month, scientists from NOAA and the U.K. Met Office published a paper, “Explaining Extreme Events of 2011 from a Climate Perspective,” in the July issue of the Bulletin of the American Meteorological Society that maps out an approach for estimating the likelihood that a given extreme weather event is a result of climate change. NOAA’s Thomas C. Peterson and Stephanie Herring, Met Office’s Peter A. Stott, and coworkers observe that “the accumulating body of evidence on the human contribution to changes in temperature extremes is robust” and that “the observed large-scale increase in heavy precipitation cannot be explained by natural internal climate variability and that human influence on climate provides a more plausible explanation.”

The scientists analyze six extreme weather events from 2011 and find that five were likely a result of human-induced climate change. The 2011 floods in Thailand, their analysis shows, were probably not influenced by climate change because the amount of rainfall was not very unusual. By contrast, drought in East Africa, unusual weather patterns in Europe, and the heat wave and drought in Texas likely were the result of climate change. They found that the events in Texas were 20 times more likely in 2011 because of climate change.

This is what a disrupted climate looks like.

Oh, and according to NOAA, “The globally averaged temperature for June 2012 marked the fourth-warmest June since record keeping began in 1880. It also marks the 36th consecutive June and the 328th consecutive month with a global temperature above the 20th-century average.” NOAA also noted that, in the U.S., “scorching temperatures during the second half of the month broke or tied over 170 all-time high-temperature records in cities across America. June temperatures also contributed to a record-warm first half of the year and the warmest 12-month period the nation has experienced since record keeping began in 1895.”

Thanks for reading.

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