The deadly Russian heat wave of 2010 was due to a natural atmospheric phenomenon often associated with weather extremes, according to a new study by scientists at the National Oceanic and Atmospheric Administration and the University of Colorado Boulder's Cooperative Institute for Research in Environmental Sciences, or CIRES.
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 used 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. The study was published in Geophysical Research Letters March 9.
"Knowledge of prior regional climate trends and current levels of greenhouse gas concentrations would not have helped us anticipate the 2010 summer heat wave in Russia," said lead author Randall Dole, deputy director of research at NOAA's Earth System Research Laboratory, Physical Science Division and a CIRES Fellow. "Nor did ocean temperatures or sea ice status in early summer of 2010 suggest what was to come in Russia."
Temperatures in the upper 90s to above 100 F scorched western Russia and surrounding areas from July through mid-August, 2010. In Moscow, the long-term daily average temperatures for July range from 65-67 F; in 2010, daily average July temperatures soared up to 87. Daily average temperatures include the night. The exceptional heat over such a long duration, combined with poor air quality from wildfires increased deaths by at least 56,000 in Moscow and other parts of western Russia, according to Munich Reinsurance, and led to massive crop failures in the region.
While a contribution to the heat wave from climate change could not be entirely ruled out, if it was present, it played a much smaller role than naturally occurring meteorological processes in explaining this heat wave's intensity, the researchers found.
They also cautioned that this extreme event provides a glimpse into the region's future as greenhouse gases continue to increase, and the signal of a warming climate, even at this regional scale, begins to emerge more clearly from natural variability in coming decades. Climate models evaluated for the new study show a rapidly increasing risk of such heat waves in western Russia, from less than one percent in 2010, to 10 percent or more by the end of this century.
"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 CIRES 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.
Authors of the new paper, "Was There a Basis for Anticipating the 2010 Russian Heat Wave?" are Randall Dole1, Martin Hoerling1, Judith Perlwitz2, Jon Eischeid2, Philip Pegion2, Tao Zhang2, Xiao-Wei Quan2, Taiyi Xu2, and Donald Murray2. The team is part of a NOAA effort to better understand the underlying causes of high-impact weather and climate events, with the ultimate goal of better anticipating them.
CIRES is a joint institute of CU-Boulder and NOAA.
Katy Human, NOAA, 303-497-4747