A sprawling global team of meteorologists who examined the marquee extreme weather events of 2012—including Hurricane Sandy, drought in the U.S. Midwest, and melting Arctic ice—found that human-induced climate change was a factor in half of the dozen events they studied.
The scientists, who published their findings Thursday in the Bulletin of the American Meteorology Society, acknowledged that determining how much influence climate change has on particular extreme weather events is an evolving science, and that better tools are needed to measure that influence.
"(W)hile climate models may indicate a human effect is causing increases in the chances of having extremely high precipitation in a region (much like speeding increases the chances of having an accident), natural variability can still be the primary factor in any individual extreme event," the authors said.
Thursday's report was written by 18 teams comprising 78 meteorologists from around the world.
Here are four of the major events analyzed by the meteorologists:
1. The devastation caused by Hurricane Sandy in October 2012. The authors were especially interested in how climate change affected Sandy's storm surge, which caused massive destruction on the coast of New Jersey and flooded parts of New York City. They concluded that the surge—a mound of water formed by a hurricane's winds and forward motion and pushed in front of the storm as it approaches landfall—was worse than it would have been in 1950 because sea level has risen in the past 60 years.
That rise in sea level has been attributed to warming temperatures and melting Arctic ice. And that rise means that future storms less powerful than Sandy are likely to cause more damage than they would have decades ago.
2. The melting of Arctic sea ice. Some computer simulations have predicted that Arctic ice will disappear during the summer by the middle of this century. The report's authors said it is "extremely unlikely that the disappearance of Arctic sea ice has been caused by natural climate variability."
3. Extreme heat and drought in the U.S. The authors said climate change had little to do with the drought in the central U.S. last year. But they added that climate change was a factor in the unusually warm weather that accompanied the drought. And climate change makes it much more likely that periods of extreme heat will happen. (Watch related video: Droughts 101.)
4. Unusually high rainfall in parts of Europe and elsewhere during 2012. The scientists reached a split decision about whether climate change was to blame for heavy rainfall in some places. Fluctuations in rainfall are normal, they said. But unusually warm sea water—which produces higher humidity and is linked to heavier rainfall—is likely caused by climate change.
The full report can be viewed here.