Met Office: Temperatures forecast to soar in ‘extreme weather’
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The new research has shown the position of the North Atlantic jets stream has changed over the last 1,250 years and has grown in intensity. The North Atlantic jet stream refers to a core of wind around five to seven miles above the Earth’s surface blowing from west to east. It causes changes to wind and pressure and is responsible for shaping some of the weather we see in the UK.
Also known as the “polar jet,’ it accounts for about 10 percent and 15 percent of the variance in annual rainfall and temperature in both eastern North America and western Europe.
The Arizona scientists found the position of the jet stream could travel outside of the range of natural variability by as early as 2060 if greenhouse gas emissions aren’t reduced.
This would bring potentially devastating weather events to both sides of the Atlantic.
But not much is known about how the jet stream varied in the past, and there is much speculation as to how it will vary in the future.
The research team collected glacial ice core samples from almost 50 sites on the Greenland ice sheet to reconstruct changes in wind across the North Atlantic dating all the way back to the eighth century.
The evidence suggests natural variability has so far hidden the effect of warming caused by human activity on what are called mid-latitude atmospheric dynamics across annual and longer timescales.
That means that it would travel away from its usual position.
Matthew Osman, from the University of Arizona, led the study.
He said: “For most places on Earth, direct climate observations typically do not span more than a few decades.
“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 and so, in terms of thinking about the future, we can now begin to use the past as a sort of prologue.”
What the study shows is that while natural variability has controlled the position of the jet stream, if global warming continues, the normal conditions over the North Atlantic could change significantly.
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Model projections show the jet stream could move further North and make the jet stream completely different within only a matter of decades.
Mr Osman also said that weather events like floods in Europe and heatwaves in the North Pacific over the summer were recent examples of how the jet stream impacts the weather based on its intensity or location in the short term.
But he also said that significant changes happen over longer periods of time too.
By reconstructing the jet stream’s past, the team found that in some years it could be far north, and could travel more than 10 degrees farther south a few years later.
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