North Atlantic jet stream may shift by 2060, leading weather extremes09/14/2021
North Atlantic jet stream could migrate NORTH by 2060 due to global warming – leading to dramatic changes in temperature and rainfall in Europe, study warns
- Experts led from the University of Arizona took samples of ice from Greenland
- They studied how the layers of snow were deposited over the last 1,250 years
- From this, they reconstructed the past locations and intensities of the jet stream
- They found that climate change has not pushed it past its natural variability yet
- But if greenhouse emissions continue apace, we will see changes in decades
- This will lead to more extreme weather like floods, droughts and heatwaves
Extreme weather may become more common across Europe and North America by 2060 as climate change shifts the North Atlantic jet stream, 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 a boost to aircraft flying from the US to Europe.
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 10–50 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.
Extreme weather may become more common across Europe and North America by 2060 as climate change shifts the North Atlantic jet stream (depicted), a study has warned
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. Pictured: one of the boreholes from which an ice core was sampled for the study. The ice comes from up to 1,000 feet deep
Between 10–50 per cent of the variation in annual precipitation and temperature in eastern North American and west Europe comes from the jet stream. Pictured: the aftermath of heavy rainfall in Verviers, Belgium, earlier this year. Jet stream changes could make extreme weather events like this a more commonplace phenomenon
HISTORICAL IMPACTS OF THE JET STREAM
Based on their reconstruction of the jet stream over the last 1,250 years, the team were able to connect shifts in the stream’s strength and position with historical weather-related disasters.
In 1374, for example, a northward shift in the jet stream led to drought and famine on the Iberian Peninsula.
Similarly, two famines across Britain and Ireland in 1728 and 1740 coincided with 50 per cent reductions in wind intensity, which would have led to cooler temperatures and less rain.
The latter is estimated to have led to the deaths of some half a million people, including 13–20 per cent of the population of Ireland.
According to Dr Osman and his team, shifts in the jet stream in the future could have similar weather, ecosystem and societal impacts.
‘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.
The North Atlantic jet steam (depicted above, over Canada) is a band of prevailing, westerly winds that encircles the Arctic — and is known for giving a boost to aircraft flying from the US to Europe . While the jet stream happens to blows hardest at airliner cruising altitudes, it also reaches down to the ground — and plays a key role in local weather conditions
Should global warming continue apace, significant changes to the North Atlantic jet stream will manifest within a matter of decades, the researchers warned — like the heat waves that struck the Pacific Northwest (causing wildfires in Canada, pictured) earlier this year
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 were able to reconstruct changes in windiness across the North Atlantic going back to the eighth century. Pictured: Dr Osman (left) and U.S. Ice Drilling Program specialist Mike Waszkiewic (right) move an ice core
‘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 Proceedings of the National Academy of Sciences.
‘Our results serve as a warning,’ said Dr Osman, who is pictured here steadying an ice core drilling barrel on the Greenland ice sheet. ‘Although pushing the jet stream beyond its natural range would be problematic, its ultimate trajectory is still largely in our control’
WHAT IS A JET STREAM?
Jet streams are fast flowing, narrow currents of air that carry warm and cold air across the planet, much like the currents of a river.
They cover thousands of miles as they meander near the tropopause layer of our atmosphere.
They are found in the atmosphere’s upper levels and are narrow bands of wind that blow west to east.
The strongest jet streams are the polar jets, found 30,000 to 39,000 ft (5.7 to 7.4 miles/ 9 to 12 km) above sea level at the north and south pole.
In the case of the Arctic polar jet this fast moving band of air sits between the cold Arctic air to the north and the warm, tropical air to the south.
When uneven masses of hot and cold meet, the resulting pressure difference causes winds to form.
During winter, the jet stream tends to be at its strongest because of the marked temperature contrast between the warm and cold air.
The bigger the temperature difference between the Arctic and tropical air mass, the stronger the winds of the jet stream become.
Sometimes the flow changes direction and goes north and south.
Jet streams are strongest – in both the southern and northern hemispheres – during winters.
This is because boundaries between cold and hot air are the most pronounced during the winter, according to the National Weather Service (NWS).
The direction the air travels is linked to its momentum as it pushes away from the earth’s equator.
‘The reason has to do with momentum and how fast a location on or above the earth moves relative to earth’s axis,’ NWS explains.
The complex interactions of many factors, including low and high pressure systems, seasonal changes and cold and warm air – affect jet streams.
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