March 10, 2011

Deadly Russian Heat Wave Was Natural: NOAA

The deadly heat wave that crippled Russia last summer was due to a natural atmospheric phenomenon often associated with weather extremes and not directly caused by global warming, according to a new study by the National Oceanic and Atmospheric Association (NOAA).

And while the scientists could not attribute the intensity of the Russian heat wave to climate change, they did find that extreme heat waves are likely to become more frequent in the region in the coming decades.

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

"We may be on the cusp of a period in which the probability of such events increases rapidly, due primarily to the influence of projected increases in greenhouse gas concentrations," said the team led by Randall Dole and Martin Hoerling of the NOAA, according to the Associated Press (AP).

"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 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."

Last summer was the warmest July on record since at least 1880 in western Russia. The heat wave was blamed for an increase in the number of deaths, as well as drought, wildfires, air pollution and severe crop damage. The high temperatures also affected the nations of Belarus, Ukraine and the Baltic nations.

The heat wave led to many questions about possible links to global warming. However, the scientists report that the heat wave was "mainly due to natural internal atmospheric variability." The cause in this case was a strong and long-lived blocking pattern that prevented movement of weather systems. Blocking patterns occur when the high-level jet stream directing the movement of weather develops a sharp wave pattern. This forces storms to move around an area while conditions are stagnate.

"Similar atmospheric patterns have occurred with prior heat waves in this region," although those have been less severe, Dole and Hoerling told AP's Randolph E. Schmid.

There were also indications the blocking pattern forcing storms to move also affected flooding in Pakistan, the researchers said.

"To be sure, it was a rare event. But rare events happen and rarity alone doesn't imply cause," Dole said at a briefing.

It is important to study the causes of events such as heat waves because they have huge impacts on the global economy, said Hoerling. The heat wave in Russia destroyed about 40 percent of grain yields, resulting in a decline in the world's grain supply. He said that researchers were surprised to find that the region had not experienced the rising temperatures that had impacted most of the planet.

"While the globe as a whole, on an annual basis, is warming, there can be important regional differences," Hoerling told AP. While last year's heat wave in Russia was devastating, the 1930s remain the warmest decade on record for western Russia, unlike the planet for a whole, for which the past 10 years have been the warmest on record, he noted.

The researchers cautioned that last year's extreme heat wave provides a glimpse into the region's future as greenhouse gases continue to increase. Climate models used by the researchers show a rapidly increasing risk of such heat waves in western Russia, from less than one percent in 2010, to ten percent or more by the end of this century.

The researchers also found that western Russia has not experienced significant climate warming in the summer months in more than 130 years, despite significant warming globally during the same 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," Hoerling said. "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."

The study -- "Was There a Basis for Anticipating the 2010 Russian Heat Wave?" -- was accepted for publication in Geophysical Research Letters, a publication of the American Geophysical Union.

The team is part of a NOAA effort to better understand the underlying causes of high-impact weather and climate events, with the goal of better anticipating them.

NOAA's mission is to understand and predict changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and to conserve and manage coastal and marine resources.


Image Caption: Smoke over western Russia on August 4, 2010. Credit: NASA/Jeff Schmaltz


On the Net: