RENEE MONTAGNE, HOST:
Across America people are sweltering through extreme heat this year, continuing a long-term trend of rising temperatures. Inevitably, many are wondering if the scorching heat is due to global warming. Scientists are expected to dig into the data and grapple with that in the months to come. They've already taken a stab at a possible connection with last year's extreme weather events, like the blistering drought in Texas. NPR's Richard Harris reports.
RICHARD HARRIS, BYLINE: Weather researchers from around the world are now taking stock of what happened in 2011. It was not the hottest year on record, but it was still in the top 15. Jessica Blunden from the National Climatic Data Center says 2011 had its own memorable characteristics.
JESSICA BLUNDEN: People may very well remember this year as a year of extreme weather and climate.
HARRIS: There were devastating droughts in Africa, Mexico, and Texas. In Thailand, massive flooding kept people's houses underwater for two months.
BLUNDEN: Here in the United States, we had one of our busiest and most destructive seasons on record in 2011. There were seven different tornado and severe weather outbreaks that each caused more than a billion dollars in damages.
HARRIS: So what's going on here? Federal climate scientist, Tom Karl, said one major feature of the global weather last year was a La Nina event. That's a period of cooler Pacific Ocean temperatures and it has effects around the globe, primarily in producing floods in some parts of the world and droughts in others.
TOM KARL: By no means did it explain all of the activity in 2011, but it certainly influenced a considerable part of the climate and weather.
HARRIS: Karl and Blunden are part of a huge multinational effort to sum up last year's weather and say what it all means. They provided an update by conference call. Clearly, long-term temperature trends are climbing as you'd expect as a result of global warming. Tom Peterson from the Federal Climate Data Center says the effort now is to look more closely at individual events.
TOM PETERSON: You've probably all heard the term you can't attribute any single event to global warming, and while that's true, the focus of the science now is evolving and moving onto how is the probability of event change.
HARRIS: And there researchers report some progress. For example, last year's record-breaking drought in Texas wasn't simply the result of La Nina. Peter Stott from the British Meteorology Office says today's much warmer planet played a huge role as well, according to the study the group released on Tuesday.
PETER STOTT: The result that they find is really quite striking, in that they find that such a heat wave is now about 20 times more likely during a La Nina year than it was during the 1960s.
HARRIS: A second study found that an extraordinary warm spell in London last November was 60 times more likely to occur on our warming planet than it would have been over the last 350 years. But that's not to say everything is related to climate change. There's no clear link between the spate of tornadoes and global warming, and devastating floods in Thailand last year, turn out to be the result of poor land use practices.
Even so, Kate Willett of the British Weather Service says there is a global trend consistent with what scientists expect climate change to bring.
KATE WILLETT: So, in simple terms, we can say that the dry regions are getting drier and the wet regions are getting wetter.
HARRIS: This year's extreme events are different from last year's, but they all fit into a coherent picture of global change. Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.