March 13, 2011 - The deadly Russian heat wave of 2010 was due to a natural atmospheric phenomenon often associated with weather extremes, according to a new NOAA study.

And while the scientists could not attribute the intensity of this particular heat wave to climate change, they found that extreme heat waves are likely to become increasingly frequent in the region in coming decades. 

The research team drew from scientific observations and computer climate models to evaluate the possible roles of natural and human-caused climate influences on the severity of the heat wave.

?It appears that parts of Russia are on the cusp of a period in which the risk of extreme heat events will increase rapidly,? said co-author Martin Hoerling, a research meteorologist, also from ESRL. Dole called the intensity of this heat wave a ?climate surprise,? expected to occur only very rarely in Russia?s current climate. With the possibility of more such events in the future, studying the Russian event better prepares scientists to understand climate phenomena that will affect the U.S. and other parts of the globe. 

The team ? led by Dole, Hoerling, and Judith Perlwitz from the Cooperative Institute for Research in Environmental Sciences at the University of Colorado in Boulder ? sifted through long-term observations and results from 22 global climate models, looking for trends that might help explain the extraordinarily high temperatures in western Russia during the 2010 summer. They also ran atmospheric models that used observed global sea surface temperatures, Arctic sea ice conditions and atmospheric carbon dioxide concentrations in 2010 to assess whether such factors might have contributed to the heat wave. 

The heat wave was due primarily to a natural phenomenon called an atmospheric ?blocking pattern?, in which a strong high pressure system developed and remained stationary over western Russian, keeping summer storms and cool air from sweeping through the region and leading to the extreme hot and dry conditions. While the blocking pattern associated with the 2010 event was unusually intense and persistent, its major features were similar to atmospheric patterns associated with prior extreme heat wave events in the region since 1880, the researchers found. 

They also found that western Russia has not experienced significant climate warming during the summer season over the 130 years from 1880-2009, despite significant warming of globally averaged temperatures during that time. Such a ?warming hole? is not unique to that region and is not entirely unexpected, as the Earth is not uniformly warming and experiences distinct geographic areas that may be warmer or cooler than the average trend. 

?We know that climate change is not taking place at the same rate everywhere on the globe,? said Hoerling. ?Western Russia is one of the parts of the world that has not seen a significant increase in summertime temperatures. The U.S. Midwest is another.? Dole compared his team?s findings to trying to hear a quiet conversation underneath the roar of a noisy fan: a summertime signal due to climate change over western Russia was drowned out by the much larger climate ?noise,? or variability, resulting from natural processes.