Russian heat wave of 2010 due to natural causes: NOAA study

The deadliest heat wave in human history--the 2010 Russian heat wave, which killed approximately 56,000 people last summer--was due to a natural atmospheric phenomenon often associated with weather extremes, according to a new NOAA study. The study, titled "Was There a Basis for Anticipating the 2010 Russian Heat Wave?" was accepted for publication in the journal Geophysical Research Letters, and used observations and computer climate models to evaluate the possible roles of natural and human-caused climate influences on the severity of the heat wave.


Figure 1. Daily Moscow temperature record from November 1 2009 to October 31 2010. Red and blue shaded areas represent departures from the long-term average (smooth curve) in Moscow. Temperatures significantly above the long-term average scorched Moscow for much of July and August. Image credit: NOAA.

Here's the body of the NOAA Press Release on the study:

"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 fellow of the Cooperative Institute for Research in Environmental Sciences (CIRES). "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 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 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.

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.

NOAA Climate Attribution: http://www.esrl.noaa.gov/psd/csi/



Figure 2. Smoke from fires in Russia on August 4, 2010 covered an area over 3,000 km (1860 miles) across. If the smoke were in the United States, it would have extended from San Francisco to Chicago. Visibility in Moscow dropped to 20 meters (0.01 miles) on August 4, and health officials warned that everyone, including healthy people, needed to take preventative measures such as staying indoors or wearing a mask outdoors. Image credit: NASA.

Commentary
Climate change has fundamentally altered Earth's atmosphere in significant ways; the additional heat and moisture in the atmosphere alters global sea surface temperature and atmospheric circulation patterns, making it difficult to disentangle to what degree an extreme weather event may be natural. The new NOAA attribution study on the Russian Heat Wave of 2010 is a reminder that the atmosphere is capable of generating extreme events on its own, without the aid of climate change. Attribution studies are difficult and take many months or years to complete. When an extreme weather event such as a great flood or deadly heat wave occurs, all we can say at the time is that climate change is loading the dice in favor of such extreme events. At the time of the Russian heat wave, I suspected that human-caused climate change was likely a significant factor, since a study of the world's previous deadliest heat wave, the 2003 European heat wave (Stott et al., 2004), found that human-caused climate change had increased the odds of that event occurring by a factor of four.

An important question to ask is if this type of natural atmospheric blocking event--where the jet stream gets "stuck" in particular contorted shape that contributes to extreme weather events--will increase or decrease in a future warmer climate. I asked climate modeling expert Dr. Ricky Rood, who writes our Climate Change blog, what the models say. His view was, "the physical basis, process, and cause and effect of blocking events are poorly understood in theory and observations and less well understood in models. It is very difficult problem, where the state-of-the-art understanding is low." So, we don't really know what will happen to blocking events in the future climate. Barnes and Hartman (2010) found that the computer models used in the 2007 [Intergovernmental Panel on Climate Change (IPCC) report generally showed a decrease in the frequency of blocking events in a future climate. This occurs because the jet stream moves poleward in a future warming climate, and the jet stream is less prone to getting "stuck" in a blocking event when it is closer to the pole. The paper summarizes previous studies on the subject thusly: "Previous studies have found evidence for blocking frequency to decrease with global warming, although they disagree on whether the duration of extreme blocking events will increase or decrease [Sillmann and Croci-Maspoli, 2009; Matsueda et al., 2009]." So, the models give us reason to hope that blocking events leading to extreme weather will decrease in the future, though the uncertainty in this prediction is high. However, the climate models used in 2010 Russian heat wave study showed a rapidly increasing risk of heat waves in western Russia, from less than one percent in 2010, to 10 percent or more by the end of this century. The authors conclude that warming attributable to increasing greenhouse gas concentrations "is very likely to produce more frequent and extreme heat waves later this century," a central finding of the 2007 IPCC report.

References
Barnes, E.A., and D.L., Hartmann, 2010, "Influence of eddy-driven jet latitude on North Atlantic jet persistence and
blocking frequency in CMIP3 integrations", GRL 37, L23802, doi:10.1029/2010GL045700, 2010

Stott, P.A. , D.A. Stone, and M.R. Allen, 2004: Human Contribution to the European heat wave of 2003. Nature, 432(7017), 610-614

I'll have a new post on Saturday at the latest.

Jeff Masters