Regional weather extremes in recent years, such as the 2011 U.S. heat wave or the 2010 Russia heat wave coinciding with the Pakistan flood, share a common physical cause, according to a new study by scientists at the Potsdam Institute for Climate Impact Research (PIK) and SFI.
The study suggests that man-made climate change repeatedly disturbs the patterns of atmospheric flow around the globe's Northern hemisphere through a subtle resonance mechanism.
SFI External Professor Hans Joachim Schellnhuber, director of PIK, is co-author of the study, which is published this week in Proceedings of the National Academy of Sciences, Online Edition.
“An important part of the global air motion in the mid-latitudes of the Earth normally takes the form of waves wandering around the planet, oscillating between the tropical and the Arctic regions. So when they swing up, these waves suck warm air from the tropics to Europe, Russia, or the US, and when they swing down, they do the same thing with cold air from the Arctic,” explains the study’s lead author, Vladimir Petoukhov.
“What we found is that during several recent extreme weather events these planetary waves almost freeze in their tracks for weeks. So instead of bringing in cool air after having brought warm air in before, the heat just stays. In fact, we observe a strong amplification of the usually weak, slowly moving component of these waves,” says Petoukhov.
Time is critical: two or three days of 30 degrees Celsius are no problem, but twenty or more days lead to extreme heat stress. Because many ecosystems and cities are not adapted to prolonged hot periods, these aberrations can result in a high death toll, forest fires, and harvest losses, suggest the authors.
The authors of the study developed equations that describe the wave motions in the extra-tropical atmosphere and show under what conditions those waves can grind to a halt and get amplified. They tested their assumptions using standard daily weather data from the U.S. National Centers for Environmental Prediction.