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NOAA Scientists Find No Clear Human Connection to Deadly 2010 Russian Heat Wave, But…

Scientists see increasing risks of similar heat waves as the world warms

Amidst last summer’s record-breaking heat wave and wildfires that enveloped Western Russia in a noxious mix of haze and smoke, the question of what role climate change played was foremost on many people’s minds. Weeks of scorching temperatures and related wildfires, which caused thousands of deaths and damaged Russia's grain supply — putting a halt to exports and raising food prices worldwide — were unlike anything in recorded Russian history.

The 2010 Russian heat wave shattered temperature records, caused thousands of deaths, devastated wheat crops, and brought intense smog to Moscow. Credit: Boris SV/flickr.

According to a new study from scientists at the National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado, Boulder, it was primarily natural atmospheric processes that caused the heat wave, and there was likely little human influence on this particular extreme event.

"The Russian heat wave was primarily due to a natural phenomenon called atmospheric blocking," explained Randall Dole, the lead author and deputy director of NOAA’s Earth System Research Laboratory in Boulder.

NOAA researchers studied both historical observations and computer model simulations to assess how much natural and human factors contributed to the extended bout of extreme heat. They found that an unusually intense area of high pressure helped cause a traffic jam of weather systems by acting as an atmospheric block, diverting weather systems around western Russia and leaving a record warm and dry airmass in place for more than a month. This particular blocking event was so large that it likely diverted cool air into southern Asia, increasing the intensity of the monsoon season around Pakistan and causing severe flooding (though the current study did not specifically examine the Pakistan floods). 

The results of the study were published today in the journal Geophysical Research Letters.

According to the U.N. Intergovernmental Panel on Climate Change's Fourth Assessment Report, the frequency of extreme heat events is expected to increase during this century as average global temperatures rise. Identifying the human influence in the behavior of extreme events, however, is still a relatively new area of climate research, and assigning human causation to individual events is even newer. There are not yet well-established protocols on how best and most robustly to compare real events with what might have happened in the absence of human-induced changes to the climate.

Following a 2003 heat wave in Western Europe, researchers from the UK’s Met Office conducted a modeling study to evaluate how much the risk of that type of extreme event had increased as a result of man-made greenhouse gas emissions. For that event, the scientists concluded with high confidence that the risk had doubled, though they cautioned that this did not mean the European heat wave was solely caused by climate change.

In light of two recent scientific studies linking greenhouse gas emissions to a higher likelihood of extreme rainfall, it appears that researchers will more commonly be investigating the potential human role in many extreme weather and climate events.  

"Climate science as we now apply it, is very much concerned with knowing what is occurring due to greenhouse gas concentrations," said meteorologist Martin Hoerling, who leads NOAA’s Climate Attribution research team and coauthored the new Russian heat wave study. Given the prediction that climate change will bring more future extreme events, Hoerling said it was natural for people to question "whether the Russian event was an early sign of this trend."

For weeks, temperatures in Moscow and throughout Western Russia were 4-5°C above seasonal averages, and as much as 2°C above the previous recorded high temperatures.

"This heat wave didn’t just break the previous records. It obliterated them," reminded Dole during a press call. “This thing was far off the charts.”

In October 2010, Climate Central conducted its own analysis of how rare the Russian event was in the context of the past 60 years, finding that the extreme temperatures Moscow saw last June, July and August “were extraordinarily intense” and the average July temperature for 2010 was warmer than any July since 1950.

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While studying climate records in Western Russia that extend further back in time, however, the researchers found there was no significant warming trend in the region over the past 130 years. Though average global temperatures have been increasing since the middle of the 20th Century, and each of the past three decades have been the warmest on record globally, the 1930s were the warmest decade around Moscow.

The trend mirrors what is observed in the American Midwest, which is another region that has not seen an increase in summer temperatures despite the global trend, says Hoerling. The researchers say these results are a reminder that while on the whole the globe is warming, there are also regional differences to understand, and that some areas may be warmer or cooler than the average trend.

Even though researchers don't expect any more or less of these blocking events with climate change, the group's climate simulations found that the risk of these types of heat waves in Western Russia is increasing because the average summer temperatures in the area are predicted to begin increasing. With higher baseline summer temperatures, even smaller systems of atmospheric blocking could result in heat waves.

A map of land surface temperature anomalies over Western Russia from July 20-27, 2010 offer a unique perspective on the record breaking heat wave. Credit: NASA

Moreover, Dole says the type of blocking event that caused the Russian heat wave can actually occur regularly and has been linked to many heat waves, though none as severe this. There is also no evidence that warm temperatures, on either the regional or global scale, can cause these blocking systems to develop, he says, explaining that they don’t expect these blocking events to occur more frequently in a warming world.

"The physical basis, process, and cause and effect of blocking events are poorly understood in theory and observations and less well understood in models,” says University of Michigan meteorologist Rick Rood, who blogs about climate change at WeatherUnderground and was not involved in the new study. “It is very difficult problem, where the state-of-the-art understanding is low."

Some meteorologists, however, have noted increasingly intense atmospheric blocking patterns in recent years, and are examining whether they may be linked to the warming atmosphere. According to the Weather Channel’s Stu Ostro, warming raises the heights of atmospheric pressure surfaces, which may alter atmospheric circulation, and Ostro says that he’s noticed a long-term trend of more frequent and intense blocking systems, like those implicated in the Russian heat wave.

If there was any human contribution to the 2010 summer heat wave, Dole says it was buried by the overwhelming influence of natural climate processes. "It’s like a quiet conversation going on beside a noisy fan – you can’t hear it." But as the rising concentration of greenhouse gases in the atmosphere affects global climate, he says the human influence will become more predominant, like a conversation getting steadily louder.

"The signal gets larger and larger, so you’ll be able to hear it."