Is the jet stream changing direction? Meandering air flow could lead to longer, harsher winters

The jet stream controls weather over Northern Europe and North America



Over the past two decades, scientists believe the jet stream has weakened

Instead of circling Earth in the north, the jet stream has begun to meander



This could cause longer and colder winters over the northern hemisphere



The fast-moving river of air that controls weather over Northern Europe and North America is undergoing a dramatic shift that could lead to harsher winters.

Scientists believe the jet stream which girdles Earth is increasingly taken a longer, meandering path causing weather patterns to become ‘stuck’.

This could result in longer and harsher winters over North America and northern Europe, according to researchers in Chicago.

The Northern Hemisphere's jet stream is a fast-moving belt of westerly winds that traverses the lower layers of the atmosphere. Experts believe it is taking a meandering path causing weather patterns to get 'stuck'



The jet stream is a ribbon of high altitude, high-speed wind in northern latitudes that blows from west to east.

It is formed when the cold Arctic air clashes with warmer air from further south. The greater the difference in temperature, the faster the jet stream moves.

According to Jennifer Francis, a climate expert at Rutgers University, the Arctic air has warmed in recent years as a result of melting polar ice caps.

This means there is now less of a difference in temperatures when it hits air from lower latitudes.

This image shows a storm passing over Britain on the jet stream last week. The jet stream is formed when the cold Arctic air clashes with warmer air from further south. The greater the difference in temperature, the faster the jet stream moves

EXPERT CLAIMS GLOBAL WARMING DID NOT CAUSE RECENT STORMS

One of the Met Office’s senior experts claims there is no link between global warming and the storms that have battered U.S. and the UK. Mat Collins, a professor in climate systems at Exeter University, said the storms have been driven by the jet stream which has been ‘stuck’ further south than usual. Professor Collins said: ‘There is no evidence that global warming can cause the jet stream to get stuck in the way it has this winter. If this is due to climate change, it is outside our knowledge.’ Professor Collins is also a senior adviser for the United Nations Intergovernmental Panel on Climate Change (IPCC). His statement appears to contradict Met Office chief scientist Dame Julia Slingo. Last weekend, she said ‘all the evidence suggests that climate change has a role to play’ in the storms. Professor Collins made clear that he believes it is likely global warming could lead to higher rainfall totals, because a warmer atmosphere can hold more water. But he said this has nothing to do with the storm conveyor belt.

‘The jet stream is a very fast moving river of air over our head,’ she said on Saturday at a meeting of the American Association for the Advancement of Science.

‘But over the past two decades the jet stream has weakened. This is something we can measure,’ she said.

As a result, instead of circling the Earth in the far north, the jet stream has begun to meander, like a river heading off course.

This has brought chilly Arctic weather further south than normal and warmer temperatures north. Perhaps most disturbingly, it remains in place for longer periods of time.

The U.S. is currently enduring an especially bitter winter, with the midwestern and southern states experiencing unusually low temperatures.

In contrast, far northern regions like Alaska are going through an unusually warm winter this year.

This suggests ‘that weather patterns are changing,’ Professor Francis said. ‘We can expect more of the same and we can expect it to happen more frequently.’

Temperatures in the Arctic have been rising ‘two to three times faster than the rest of the planet,’ said James Overland, a weather expert with the National Oceanic and Atmospheric Administration (NOAA).

This photograph shows waves crashing into Southsea in Hampshire on Friday night. Scientists believe changes to the jet stream could create permanent harsher winters

Professor Francis added that it is premature to blame humans for these changes.

‘Our data to look at this effect is very short and so it is hard to get very clear signal,’ she said.



‘But as we have more data I do think we will start to see the influence of climate change.’

The meandering jet steam phenomenon, sometimes called ‘Santa's Revenge’, remains a controversial idea.

‘There is evidence for and against it,’ said Mark Serreze, director of the National Snowland Ice Data Centre in Boulder, Colorado.

But he said rising Arctic temperatures are directly linked to melting ice caps.

‘The sea ice cover acts as a lid which separates the ocean from a colder atmosphere,’ Mr Serreze told the conference.

But if the lid is removed, then warmth contained in the water rises into the atmosphere.

This warming trend and the shifting jet stream will have a dire impact on agriculture, especially in the farm-rich middle-latitudes in the U.S..

‘We are going to see changes in patterns of precipitation, of temperatures that might be linked to what is going on in the far north,’ said Mr Serreze.