The North Atlantic Jet Stream, a rapid air stream circling the northern hemisphere, could migrate north over the next few decades if strong global warming continues.
The consequences could be dramatic: changes in precipitation patterns across mid-latitudes and an increase in droughts, heat waves, floods and other extreme weather events in Europe and the eastern United States.
A new study notes that the jet stream could move beyond its historic range in just a few decades – by around 2060 – under a severe warming scenario. The results were published last week in the journal Proceedings of the National Academy of Sciences.
The effect of climate change on the jet stream is a hot topic among scientists. The jet stream has a powerful influence on weather and climate conditions throughout the northern hemisphere, and changes in the strength or position of the air stream can have great ripple effects all over the world.
Many scientists believe that rising air temperatures can affect the flow of the jet stream. The current exists because of the large temperature difference between the freezing North Pole and the hot equator. This temperature gradient affects the thickness of the atmosphere, giving rise to undulating air currents that circulate from west to east around the globe.
Today, these air temperatures keep rising. But not all regions of the world are warming at the same rate. And since some regions heat up faster than others – the rapidly warming Arctic, in particular – scientists believe they can cause changes in the atmosphere that affect airflow.
Some experts believe these changes may alter the jet stream.
But not everyone agrees on how the jet stream might change – or if climate change has already had a noticeable effect on it. The jet stream tends to move a lot as is, moving north and south and wiggling up and down as it moves around the globe. It can be difficult to determine whether recent fluctuations are within its normal limits or not.
The new study, led by Matthew Osman of the University of Arizona, aimed to get to the bottom of this.
Osman and his colleagues set out to trace the position of the jet stream throughout history, going back thousands of years in the past. They did so using a practical scientific trick, by chemically analyzing samples of ancient ice drilled from the depths of the Greenland ice sheet.
Ice cores, as scientists call them, work much like a scientific time machine. They contain all kinds of information about what the climate was like thousands of years ago.
And because the jet stream has such a big effect on regional weather and climate, scientists can use this information to map the flow of the jet stream through history.
In this case, researchers have been able to reconstruct its position over the past 1,250 years.
They found that the position of the jet stream – how far north or south it travels – tends to move a lot. But so far all the changes are still within the range of its historical natural fluctuations.
But that won’t necessarily be the case for long. The researchers used climate models to simulate the jet stream in a warmer world. If the planet continues to warm at a high rate, the jet stream will likely move north over time.
In fact, the study suggests, global warming may have already started pushing it toward the poles – it just hasn’t quite gone beyond its normal range yet. But it could settle firmly outside its natural limits within 40 years.
This could cause major climate changes in mid-latitudes, especially in Europe.
The jet stream helps transport precipitation systems to southern Europe, which would otherwise be relatively dry. If the jet stream moves north, it could take this precipitation with it, increasing the risk of drought.
“You’re really going to focus on the areas that really depend on a jet stream that exists within its natural limits,” Osman told E&E News.
Some parts of Europe could also experience an increase in flooding and heat waves.
In North America, a northward moving jet stream could amplify warming on the east coast and increase the severity of some extreme weather events.
Yet, says Osman, “there is reason to be optimistic here.”
The new study used climate simulations that assume high greenhouse gas emissions and significant warming in the future. This is a scenario that is already relatively unlikely in the real world, as nations around the world strive to reduce their carbon emissions.
In a more moderate warming scenario – a scenario more in line with current global climate action – the jet stream is likely to move northward over time, but likely at a slower rate, Osman suggested.
“I want to stress that these are model scenarios for the future,” Osman warned. “Ultimately, its trajectory into the future is still largely in our control.”
A climate controversy
The global position of the jet stream is not the only topic of interest among climatologists.
Some experts believe that climate change can also make the jet stream ‘ripple’, causing it to rise and fall more sharply as it travels around the world. Waves in the jet stream can also worsen extreme weather events, sometimes causing storm systems or heat waves to slow down or block.
Osman’s team did not report any information in their ice core analyzes that would indicate a change in ripple over time. But that’s also not what their method was designed to seek, he warned.
At the same time, the position of the jet stream and its ripple could be related. According to James Screen, a climatologist at the University of Exeter, some experts believe that a northward shift could result in a stronger, less wavy jet stream. A move south would lead to the opposite.
If the jet stream does indeed move north over the next several decades, one would expect fewer ripples, he said.
It is a subject of debate among climatologists. Some studies suggest that the jet stream is already agitating over time. These changes could be caused by atmospheric changes linked to the rapid warming of the Arctic, according to some experts.
Jennifer Francis, a climatologist at the Woodwell Climate Research Center, has devoted much of her recent career to studying arctic warming and large air currents like the jet stream. Some studies suggest there may be some sort of “tug of war” right now, she told E&E News. Some effects of climate change on the atmosphere can push the jet stream north, while others could pull it south.
Other experts are not convinced that the warming of the Arctic is affecting the ripple of the jet stream at all – at least, not yet.
Screen, the University of Exeter scientist, published research suggesting that any recent changes in jet stream ripple are likely natural fluctuations rather than direct consequences of arctic warming.
The subject remains a major issue in climatology.
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2021. E&E News provides essential information for energy and environment professionals.