The world has suffered from severe regional weather extremes in recent years, such as the heat wave in the United States in 2011 or the one in Russia 2010 coinciding with the unprecedented Pakistan flood. Behind these devastating individual events, scientists at the Potsdam Institute for Climate Impact Research (PIK) claim there is a common physical cause: Man-made climate change repeatedly disturbs the patterns of atmospheric flow around the globe's Northern hemisphere through a subtle resonance mechanism.
Air normally travels around the planet in the form of waves, oscillating between the tropical and Arctic regions. The researchers found during several recent extreme weather events that these planetary waves got stuck for weeks on end. "So instead of bringing in cool air after having brought warm air in before, the heat just stays", explains lead author Vladimir Petoukhov. Since many ecosystems and cities are not adapted to prolonged hot periods, this can result in a high death toll, forest fires, and dramatic harvest losses.
Climate change caused by greenhouse gas emissions from burning fossil fuels does not mean uniform global warming: In the Arctic, the relative increase of temperatures is higher than average, which in turn actually reduces the temperature difference between the Arctic and, for example, Europe. However, as the scientists explain, temperature differences are a main driver of air flow. Additionally, continents generally warm and cool more readily than the oceans. "These two factors are crucial for the mechanism we detected", says Petoukhov. "They result in an unnatural pattern of the mid-latitude air flow, so that for extended periods the slow synoptic waves get trapped."