Climate change: North Atlantic jet stream could migrate north by 2060, leading to extreme weather
Extreme weather may become more common across Europe and North America by 2060 as shifts the , a study has warned. The North Atlantic jet steam is a band of prevailing, westerly winds that encircles the Arctic, and is known for giving . While the jet stream happens to blow hardest at airliner cruising altitudes, it also reaches down to the ground, and plays a key role in local weather conditions. In fact, between 1050 per cent of the variation in annual precipitation and temperature in eastern North American and west Europe comes from the jet stream. The heatwave this summer in the Pacific Northwest and the floods that hit Europe are just a couple of examples of how jet steam variations can impact the weather. Despite its importance, however, not much is known about how the jet stream differed in the past and, by extension, how it might change in the future. Experts led from the University of Arizona drilled into Greenland's ice sheets extract a record of past weather conditions going back some 1,250 years. They found that, so far, the impact of human-caused warming on the jet stream has been less that the natural variations seen in the air current's recent history. However, their projections suggest that business-as-usual greenhouse emissions will push the jet stream northwards, leading to significant changes in mere decades. 'For most places on Earth, direct climate observations typically do not span more than a few decades,' said paper author and climate scientist Matthew Osman of the University of Arizona. 'So, we haven't had a great sense of how or why the jet stream changes over longer periods of time. 'What we do know is that extraordinary variations in the jet stream can have severe societal implications such as floods and droughts due to its impacts on weather patterns,' he continued. 'So, in terms of thinking about the future, we can now begin to use the past as a sort of prologue.' In their work, Dr Osman and colleagues analysed ice cores collected from nearly 50 sites across the Greenland ice sheet. From these natural records, the team was able to reconstruct changes in windiness across the North Atlantic on a year-to-year basis going back to the eighth century. They did this by looking at the amount of snowfall deposited each year as well as the chemical makeup of the water molecules that made up each snow layer. 'These layers tell us about how much precipitation fell in a given year and also about the temperatures that airmasses were exposed to,' explained Dr Osman. The team found that, to date, fluctuations in the jet stream's intensity and position are within the limits of natural variation. However, they calculated, should global warming continue apace, significant changes will manifest within a matter of decades, with the jet stream expected to migrate its average position northwards. 'Such variations have huge implications on the types of weather that people might experience at a given place,' said Dr Osman. 'For example, when the jet stream is situated further south, the normally dry Iberian Peninsula tends to experience milder, moister conditions. 'But, as the jet stream migrates northward, much of that moisture also moves away from Iberia towards already-wet regions of Scandinavia. 'A poleward-shifted jet stream in the future thus might have similar, but more permanent, consequences.' That said, the team did find evidence of societally significant shifts in the jet stream's history, sometimes drifting north, only to be more than 10 south mere years later. 'Our results serve as a warning,' added Dr Osman. 'Although pushing the jet stream beyond its natural range would be problematic, its ultimate trajectory is still largely in our control.' The full findings of the study were published in the journal .