Scientific American: Extreme Weather Caused by Climate Change
June 28, 2011
“More violent and frequent storms, once merely a prediction of climate models, are now a matter of observation.”
So begins a three part series in Scientific American. Despite the protestations of the climate denial choir, the meaning of this years extreme events are becoming clear to the scientific community.
“..are the floods and spate of other recent extreme events also examples of predictions turned into cold, hard reality?
Increasingly, the answer is yes. Scientists used to say, cautiously, that extreme weather events were “consistent” with the predictions of climate change. No more. “Now we can make the statement that particular events would not have happened the same way without global warming,” says Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research (NCAR) in Boulder, Colo.
That’s a profound change—the difference between predicting something and actually seeing it happen. The reason is simple: The signal of climate change is emerging from the “noise”—the huge amount of natural variability in weather.
The data show that the number of such events is rising. Munich Re, one of the world’s largest reinsurance companies, has compiled the world’s most comprehensive database of natural disasters, reaching all the way back to the eruption of Mount Vesuvius in A.D. 79. Researchers at the company, which obviously has a keen financial interest in trends that increase insurance risks, add 700 to 1,000 natural catastrophes to the database each year, explains Mark Bove, senior research meteorologist in Munich Re’s catastrophe risk management office in Princeton, N.J. The data indicate a small increase in geologic events like earthquakes since 1980 because of better reporting. But the increase in the number of climate disasters is far larger. “Our figures indicate a trend towards an increase in extreme weather events that can only be fully explained by climate change,” says Peter Höppe, head of Munich Re’s Geo Risks Research/Corporate Climate Center: “It’s as if the weather machine had changed up a gear.
The second line of evidence comes from a nascent branch of science called climate attribution. The idea is to examine individual events like a detective investigating a crime, searching for telltale fingerprints of climate change. Those fingerprints are showing up—in the autumn floods of 2000 in England and Wales that were the worst on record, in the 2003 European heat wave that caused 14,000 deaths in France, in Hurricane Katrina—and, yes, probably even in Nashville. This doesn’t mean that the storms or hot spells wouldn’t have happened at all without climate change, but as scientists like Trenberth say, they wouldn’t have been as severe if humankind hadn’t already altered the planet’s climate.This new science is still controversial. There’s an active debate among researchers about whether the Russian heat wave bears the characteristic signature of climate change or whether it was just natural variability, for instance. Some scientists worry that trying to attribute individual events to climate change is counterproductive in the larger political debate, because it’s so easy to dismiss the claim by saying that the planet has always experienced extremeweather. And some researchers who privately are convinced of the link are reluctant to say so publicly, because global warming has become such a target of many in Congress.