Study finds man-made imprint on nine climate extremes

WASHINGTON – Scientists looking at 16 cases of wild weather around the world last year see the fingerprints of man-made global warming on more than half of them.

Researchers found that climate change increased the odds of nine extremes: heat waves in Australia, Europe, China, Japan and Korea; intense rain in parts of the United States and India; and severe droughts in California and New Zealand. The California drought, though, comes with an asterisk.

Scientists couldn’t find a global warming link to an early South Dakota blizzard, freak storms in Germany and the Pyrenees, heavy rain in Colorado, southern and central Europe, and a cold British spring.

Organized by the U.S. National Oceanic and Atmospheric Administration, researchers Monday published 22 studies on 2013 climate extremes in a special edition of the Bulletin of the American Meteorological Society.

“It’s not ever a single factor that is responsible for the extremes that we see,” said Tom Karl, NOAA National Climatic Data Center director. “Natural variability is always part of any extreme climate event.”

For years, scientists said they could not attribute single weather events – like a drought, heat wave or storm – to man-made global warming. But with better computer models and new research, in some cases scientists can see how the odds of events increase – or not – because of climate change. Other researchers question the usefulness and accuracy of focusing on single, extreme events.

The editors of the 108-page compilation of studies wrote that people and animals tend to be more affected by extreme weather than changes in averages, so they pay attention to it. The public often connects extreme events to climate change, sometimes wrongly, so scientific analysis like this “can help inform the public’s understanding of our changing environment.”

The influence on Australia’s hottest year in more than a century is glaring, the report’s editors said.

“It’s almost impossible” to explain Australia’s hot 2013 without climate change, said Peter Stott of the United Kingdom’s meteorology office, a report editor.

The most complicated issue is the California drought, the only extreme that has continued into this year.

Three teams studied that state’s record drought in different ways. Two teams couldn’t find a link to global warming and water and air temperatures, but the third from Stanford University looked at high pressure patterns in the air and found a connection.

Earlier peer-reviewed studies looking at atmospheric patterns have connected California’s drought to climate change. However, the editors of the journal’s special edition said it is unclear whether a global warming connection can be pinned on California’s drought.