They're raging a continent apart, but two deadly natural disasters—the Russian wildfires and the Pakistan floods—may be connected by the Asian monsoon, one of the most powerful atmospheric forces on the planet, scientists say.
That's because the monsoon—a seasonal wind system that brings rain and floods to Pakistan and much of the rest of Asia in summer—also drives the circulation of air as far away as Europe, said Kevin Trenberth, a senior scientist at the Boulder, Colorado-based National Center for Atmospheric Research.
(Related: "Chinese Kingdoms Rose, Fell With Monsoons?")
Air pumped into the upper atmosphere by monsoon winds has to come down somewhere. And with the monsoon's giant reach, much of that air seems to be settling over Russia, where it's creating high-pressure conditions, which favor heat waves, Trenberth said. Near high-pressure systems, air tends to sink, which discourages clouds from forming.
Such circulation patterns are normal, but they're also being enhanced by rising sea temperatures due in part to global warming, he added.
For instance, the northern Indian Ocean has warmed 2 degrees Fahrenheit (1.1 degrees Celsius) since the 1970s. Warmer water releases more moisture into the air, which can supercharge monsoon rains.
"The key message is that it's not just natural variability and not just global warming" but a combination of both, Trenberth said. For instance, the last months of a recent El Niño—a cyclical warming of tropical waters in the central and eastern Pacific Ocean—likely contributed to the high sea temperatures in the Indian Ocean.
He also cautioned that the monsoon link between the Russia fires and Pakistan floods is difficult to prove, since it's based on observations and interpretations of past research.
Fires, Floods, Heat: Record-Breaking Extremes in 2010
This year's fierce monsoon rains have spawned Pakistan's worst flooding in 80 years, affecting nearly 14 million people, according to the New York Times.
And in Russia, widespread fires are stoked by the worst heat wave in Russian memory. Around Moscow, choked with fire-related smog, temperatures have hovered around 100 degrees Fahrenheit (38 degrees Celsius) for weeks and show no sign of letting up soon, according to the Bloomberg news agency.
(Related blog post: "Russia Burns in Hottest Summer on Record.")
Trapping the smoke are anticyclones, atmospheric high-pressure centers that occur when monsoon winds form a stable layer of air a few thousand feet above Earth's surface.
Both Russia and Pakistan are also experiencing "remarkable" temperatures in 2010, which is shaping up to be one of the hottest years since record-keeping began in the late 1880s, Jeff Masters, director of meteorology for the Weather Underground website, told National Geographic News in July.
Nine countries have shattered heat records, including Pakistan, which on May 26 logged a mercury reading of 128.3 degrees Fahrenheit (53.5 degrees Celsius)—the highest ever seen in Asia, Masters said.
Extreme events such as heat waves, drought, and monsoon floods are believed by some scientists to be increasing with global warming, and the disasters in Russia and Pakistan may be indications of this, Rosanne D'Arrigo, a research professor at Columbia University's Lamont-Doherty Earth Observatory, said in an email. (See a world map of potential global warming impacts.)
However, D'Arrigo said, it's not possible to ascribe any one event to global warming.
Atmospheric "Logjam" Prolonging Russia Fires, Pakistan Floods
D'Arrigo added that there's a "possible relationship" between the monsoon and the fires—for instance, the Asian monsoon has been linked before in various ways to higher-latitude conditions, such as in the North Atlantic, she said.
Deke Arndt, head of the Climate Monitoring Branch of the U.S. National Oceanic and Atmospheric Administration's National Climatic Data Center, agreed it's likely that the fires can be traced back to the monsoon.
He noted that the events may also be prolonged by an atmospheric "logjam" that's common in the summer but which has been unusually "stubborn and long-lasting" this year.
The blockage occurs when atmospheric winds lock climate phenomena—such as large storms or heat waves—into place for a long period of time. In the United States in the summer, for example, storms will "squat on a place and sit and spin for a week," Arndt said.
"These features, while they're strong, are also really persistent," he said. They "show up [as] day after day of rainfall in India and Pakistan ... and day after day of oppressive conditions in western Russia."
Overall, scientists often struggle to quantify how the climate fits in with such natural occurrences, Arndt said.
But the likely link between the Russian fires and the Pakistan floods "is a great example that things that happen in the atmosphere don't occur in isolation."