Global Warming

Climate change is shifting global air currents

Huge jetstreams that circle Earth are being altered by climate change, scientists have warned.

The researchers claim that man-made global warming has slowed down the way that air flows and distributes weather - and the consequences could be severe.

They say the shift will see an increase in extreme weather globally, including more deadly droughts, floods and heatwaves.

Jetstreams are influenced by the difference in temperatures between the equator and the Arctic. These streams circle the Earth and transport heat and moisture from the Arctic to the tropics. But when the planetary waves stall droughts or floods can occur.

Warming caused by greenhouse-gases from fossil fuels stall airstreams, the international team of researchers found.

They found changes that show extreme and persistent shifts in the jet stream that can trigger extreme weather events. Human activity has been suspected of contributing to this pattern before, but the researchers say they have now uncovered a 'clear fingerprint' of human activity. 'If the same weather persists for weeks on end in one region, then sunny days can turn into a serious heat wave and drought, or lasting rains can lead to flooding,' explains co-author Professor Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research (PIK) in Germany. 'This occurs under specific conditions that favour what we call a quasi-resonant amplification that makes the north-south undulations of the jet stream grow very large. It also makes theses waves grind to a halt rather than moving from west to east. Identifying the human fingerprint on this process is advanced forensics.'

Since the Arctic is more rapidly warming than other regions, its temperature difference with the equator is decreasing.

Also, land masses are warming more rapidly than the oceans, especially in summer. Both changes have an impact on those global air movements. This includes the giant airstreams that are called planetary waves because they circle Earth's Northern hemisphere in huge turns between the tropics and the Arctic.

When airstreams stall thanks to man-made temperature rises droughts or floods can occur. This image shows before (2011) and after (2014) photos of the Enterprise Bridge over Lake Oroville in Butte County, California after recent droughts: