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And I'm Melissa Block.
Scientists have been saying for years that as the planet heats up, there will be more severe weather. But it's hard to pin any one event - such as a particular hurricane - on global warming. Now, scientists have tried to do just that.
As NPR's Richard Harris reports, they've linked cases of extreme precipitation to global warming.
RICHARD HARRIS: Here's the thing about climate change - Myles Allen at Oxford University says it's hard to feel the effects of a slowly warming planet.
MYLES ALLEN: One of the problems I think many people find with climate change is it's sort of a victimless crime, in the sense that the impacts are largely hypothetical for many people.
HARRIS: But climate change isn't just about a gradual temperature rise. Many studies forecast more extreme weather, like stronger hurricanes and bigger downpours. Even so, Allen told the press briefing, it's hard to look back at something like Hurricane Katrina or Europe's devastating heat wave of 2003 and say that it was the result of global warming.
ALLEN: It is a reasonable question, you know, is human influence on climate anything to do with this nasty bit of weather we're having? But answering it isn't easy.
HARRIS: Allen and his colleagues have just taken a stab at it. They focused on some major flooding in England and Wales back in the fall of 2000.
NPR's Julie McCarthy covered the record-shattering deluge.
JULIE MCCARTHY: With rain lashing the west, freak tornados struck the south and blizzards swept the north to Scotland. The extreme...
HARRIS: The question is: Would this have happened in the absence of the global warming we've experienced to date? To find out, Allen's colleague, Pardeep Pall at Oxford, explains they ran thousands of computer simulations of the climate on thousands of computers. They compared simulated worlds with and without global warming.
PARDEEP PALL: To do that repetition, the thousands of repetitions would've been pretty tough to do all by ourselves, so we actually asked members of the public across the world to run our simulations for us on their own personal computers, using their idle time. And this was done via the climateprediction.net project.
HARRIS: And they report in nature that the extreme rainfall was far more likely to appear in the computer simulations of our current climate than in a world without global warming. So they're fairly confident in saying that the flooding was linked to global warming.
Allen says the excessive rainfall is pretty simple to explain.
ALLEN: It's largely driven by the fact that the air is just warmer and, therefore, holding more water.
HARRIS: Now, this particular experiment took a huge amount of computing power, so it's not something that climate scientists can do routinely. But Allen hopes the day will come when analysis like this will become routine after major events.
ALLEN: It won't be enough for your weather service to predict the weather. They'll have to explain it as well.
HARRIS: And Allen hastens to add that not all extreme weather events can be blamed on climate change. The world has always had bad weather, and it will keep having bad weather.
Now, a second study in Nature asks a much broader question and that is whether the worst downpours are getting even more extreme over time.
Author Francis Zwiers from the Pacific Climate Impacts Consortium in British Columbia says yes.
FRANCIS ZWIERS: Extreme precipitation events today are generally a fair bit larger than they were in the 1950s and '60s.
HARRIS: And he attributes at least some of that increase to humans warming the planet. Some scientists not involved in these studies find them provocative but not convincing. Here's Kerry Emanuel from MIT.
KERRY EMANUEL: I think it's going to be very tough ever to do individual events. The only exception are events that are so extreme that they couldn't have occurred in the current climate. But proving that is difficult.
HARRIS: The trend is clearly toward a warmer world with more severe weather, but it's still going to be hard to blame humans for any single disaster.
Richard Harris, NPR News.