NEW YORK — Last year brought a record heat wave to Texas, massive floods in Bangkok and an unusually warm November in England. How much has global warming boosted the chances of events like that?
Quite a lot in Texas and England, but apparently not at all in Bangkok, say new analyses released Tuesday.
Scientists can’t blame any single weather event on global warming, but they can assess how climate change has altered the odds of such events happening, said Tom Peterson of the National Oceanic and Atmospheric Administration, the editor of a report that includes the analyses published by the Bulletin of the American Meteorological Society.
In the Texas analysis, researchers at Oregon State University and in England noted that the state suffered through record heat last year during a La Niņa weather pattern. Caused by the cooling of the central Pacific Ocean, La Niņa generally cools global temperatures but would be expected to make the southern U.S. warmer and drier than usual. But beyond that, the scientists wondered, would global warming affect the chances of such an event happening?
To find out, they studied computer climate simulations for La Niņa years, focusing on Texas. They compared the outcome of three such years in the 1960s with that of 2008. The idea of the study, they said, was to check the likelihood of such a heat wave both before and after there was a lot of man-made climate change, which is primarily from burning fossil fuels like coal and oil. Their conclusion: Global warming has made such a Texas heat wave about 20 times more likely to happen during a La Niņa year.
Using a similar approach, scientists from Oxford University and the British government looked at temperatures in central England. Last November was the second warmest in that region in more than 300 years. And December 2010 was the second coldest in that time. Their analysis concluded that global warming has made such a warm November about 62 times more likely, but such a cold December half as likely.
A third analysis considered unusually severe river flooding last year in central and southern Thailand, including neighborhoods in Bangkok. It found no sign that climate change played a role in that event, noting that the amount of rainfall was not very unusual. The scale of the flooding was influenced more by factors like reservoir operation policies, researchers wrote.