Two teams of researchers find that subtle changes brought about by global warming might be amplifying atmospheric blocking patterns, which keep weather conditions in place for a long time.
As the summer of 2012 winds down, with drought and searing temperatures its hallmark for much of the continental United States, researchers are trying to get a better handle on the factors that contribute to the persistence of weather patterns responsible for the extremes.
The immediate culprit: patterns of atmospheric flow that steer storms along a given path for weeks, heating and depriving some areas of needed rain while drenching others. Such blocking patterns are a global phenomena, a normal component of Earth's weather systems.
But some researchers suggest that global warming's influence on the Arctic and on the tropics can change circulation patterns in ways that keep blocking patterns in place longer than they otherwise might.
For the continental US, blocking has been a byword for much of the year. The first eight months of 2012 have gone into the books as the warmest January-August period on record for the continental US, according to the National Oceanic and Atmospheric Administration's National Climatic Data Center in Asheville, N.C. The 12-month span ending in August 2012 was the warmest 12 months on record. The summer itself ranks third among the warmest summers on record.
At the end of August, 62.9 percent of the continental US was experiencing moderate to exceptional drought.
Page 1 of 4