Weather Extremes May be on the Rise and Triggered by Atmospheric Waves

Weather extremes are continuing to cause problems across the world. Hotter summers, colder winters and stronger storms can play havoc on populations. While human-caused global warming might explain a gradual increase in periods of severe heat, though, other events are not so easily explained. Now, scientists may have found an answer.

"The large number of recent high-impact extreme weather events has struck and puzzled us," said Dim Coumou, lead author of the new study, in a news release. "Of course we are warming our atmosphere by emitting CO2 from fossil fuels, but the increasei n devastating heat waves in regions like Europe or the U.S. seems disproportionate."

In order to find out what might be causing weather extremes, the researchers turned to circulation patterns. An important part of the global air motion in the mid-latitudes takes the form of waves wandering around the globe, called Rossby Waves. When they swing north, they suck warm air from the tropics to Europe, Russia or the U.S. When they swing south, they do the same thing with cold air from the Arctic. Yet with recent temperature fluctuations, some of these waves have become virtually stalled and greatly amplified.

The researchers used advanced data analysis to get a better close at these waves. This allowed them to see when certain resonance conditions are fulfilled, the atmosphere tends to develop anomalously slowly propagating waves with large amplitudes, typically associated with extreme weather on the ground. The scientists also found that this phenomenon is occurring more often; in fact, after 2000, it's almost twice as frequent as before.

"Evidence for actual changes in planetary wave activity was so far not clear," said Stefan Rahmstorf, co-author of the new study. "But by knowing what patterns to look for, we have now found strong evidence for an increase in these resonance events."

The findings reveal that extreme weather events may just be on the rise. Not only that, but it could be caused by warming temperatures. As the Arctic warms, temperature difference to other regions decreases and can impact wave patterns.

The findings are published in the journal Proceedings of the National Academy of Sciences.