WASHINGTON — A study of a dozen of 2012’s wildest weather events found that man-made global warming increased the likelihood of about half of them, including Superstorm Sandy’s devastating surge and the blistering U.S. summer heat.
The other half — including a record wet British summer and the U.S. drought last year — simply reflected the random freakiness of weather, researchers with the U.S. National Oceanic and Atmospheric Administration and the British meteorological office concluded in a report issued Thursday.
The scientists conducted thousands of runs of computer simulations that looked at factors, such as moisture in the air, atmospheric flow, and sea temperature and level.
Scientists used to say that individual weather events — a specific hurricane or flood, for example — cannot be attributed to climate change. But recently, researchers have used computer simulations to look at extreme events in a more nuanced way and measure the influence of climate change on their likelihood and magnitude.
The researchers said climate change had made these 2012 events more likely: U.S. heat waves, Superstorm Sandy flooding, shrinking Arctic sea ice, drought in Europe’s Iberian peninsula, and extreme rainfall in Australia and New Zealand.
However, the 78 international researchers found no global warming connection for the U.S. drought, Europe’s summer extremes, a cold spell in the Netherlands, drought in eastern Kenya and Somalia, floods in northern China and heavy rain in southwestern Japan.
That doesn’t mean that there weren’t climate change factors involved, just that researchers couldn’t find or prove them, said the authors of the 84-page study, published in the Bulletin of the American Meteorological Society.