Russia's killer heat wave and monster South Asian monsoon floods could be more than isolated examples of extreme weather. Though separated by a continent, they could be linked.

Monsoon rains drive air upward, and that air has to come down somewhere. It usually comes down over the Mediterranean, producing the region's hot, dry climate. This year, some of that air seems to have gone north to Russia.

"We haven't done the studies, but there's very good reason to suspect that there's a relationship," said Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research. "It's simply related to the idea that there is a monsoon with very large circulation. There's an upwards branch of it. There has to be a downwards branch somewhere else."

The Russian heat wave has persisted since late June, with daytime temperatures at least 12 Fahrenheit degrees above normal – and often much more – for over a month. In Moscow alone, an estimated 300 people a day have died. The temperatures threaten wheat harvests and have sent global prices rising in a manner reminiscent of the lead-up to 2008's global food riots.

Weather Underground meteorologist Jeff Masters called it "one of the most remarkable weather events of my lifetime," which is probably an understatement. Russian meteorologists say it's the most intense heat wave in a millennium.

Meanwhile, in South Asia and China, seasonal monsoons have been exceptionally intense, setting off the worst flooding in 80 years. Pakistan has been especially hard-hit, with 1,600 people dead and 2 million homeless in what's been dubbed "Pakistan's Katrina."

Events like these fit with general forecasts of weather trends in a warming climate. But some observers have wondered whether Russia's heat wave and Asia's floods are linked not just by a vague trend, but by specific cause-and-effect meteorological dynamics. They will undoubtedly be studied in detail for years to come, but according to Trenberth, there's good reason to think the extremes are connected.

"The two things are connected on a very large scale, through what we call an overturning or monsoonal circulation," he said. "There is a monsoon where upwards motion is being fed by the very moist air that's going onshore, and there are exceptionally heavy rains. That drives rising air. That air has to come down somewhere. Some of it comes down over the north."

Fueling the monsoons' intensity are warmer-than-usual temperatures in and above the Indian Ocean. At 2 Fahrenheit degrees above late-20th century levels, the air can hold about 8 percent more water. At higher temperatures, the air is also more buoyant, and "invigorates the storms," said Trenberth.

"Air rises faster than before. It sucks more air in. It changes moisture flow onto land even more. You can almost double the effect," he said. "From that 8 percent more water, there can be 16 percent more rainfall."

As for why some of that surging monsoon air may have fallen to Earth over Russia this year, Trenberth declined to speculate. Historical weather patterns do, however, suggest linkages across the Northern Hemisphere's middle latitudes, intermittently coupled in turn to India's summer monsoon cycles.

Russia's heat wave could simply be part of that pattern, exacerbated this year by heat absorbed in Russia's Arctic – where sunlight-reflecting sea ice is reaching all-time lows – and by heat-trapping soot particles from wildfires raging in western Russia. Trenberth added that large-scale rainfall events "tend to create more persistent weather patterns elsewhere," creating heating patterns that lock atmospheric flows into place.

Vladimir Petoukhov, a climate modeler at Germany's Potsdam Institute, agreed that a link is possible. "Different geographic locations of the Northern Hemisphere could be simultaneously subjected to drought-like and flood-like conditions," he said. "These phenomena cannot be regarded as solitary local structures."

As regional temperatures continue to rise, "the frequency of such events could markedly increase," said Petoukhov.

Images: 1) Heat anomaly map of Eurasia in late July. The darkest red areas are 22 Fahrenheit degrees warmer than usual, and the darkest blue areas are 22 degrees cooler./NASA. 2) The Indus river floodplain in Pakistan as photographed July 18 (top) and Aug. 8 (bottom)./NASA.

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