The North Atlantic jet stream, a fast-moving air current circling the Northern Hemisphere, may migrate northward in the coming decades if strong global warming continues.
The consequences could be dramatic: shifts in rainfall patterns across the midlatitudes and an increase in droughts, heat waves, floods and other extreme weather events in Europe and the eastern U.S.
A new study finds that the jet stream could shift outside the bounds of its historic range within just a few decades — by the year 2060 or so — under a strong warming scenario. The findings 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 patterns throughout the Northern Hemisphere, and changes in the strength or the position of the air current can have big ripple effects around the world.
Many scientists believe rising air temperatures can affect the jet stream’s flow. The current exists because of the strong difference in temperatures between the icy North Pole and the warm equator. This temperature gradient affects the thickness of the atmosphere, giving rise to wavy air currents that flow from west to east around the globe.
Today, these air temperatures are steadily climbing. But not all parts of the world are warming at the same rate. And as some regions heat up faster than others — the rapidly warming Arctic, in particular — scientists believe they may cause shifts in the atmosphere that affect the flow of air.
Some experts believe these shifts may alter the jet stream.
But not everyone agrees on exactly how the jet stream might change — or whether climate change has had any noticeable effect on it yet. The jet stream tends to move around a lot as it is, shifting north and south and wiggling up and down as it moves around the globe. It can be hard to parse out whether recent fluctuations are within its normal boundaries or not.
The new study, led by Matthew Osman of the University of Arizona, aimed to get to the bottom of it.
Osman and his colleagues set out to trace the jet stream’s position through history, looking back thousands of years into the past. They did so using a handy scientific trick, chemically analyzing samples of ancient ice drilled from deep within the Greenland ice sheet.
Ice cores, as scientists call them, work a bit 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 strong effect on regional weather and climate patterns, scientists can use this information to map out the flow of the jet stream through history.
In this case, researchers were able to reconstruct it 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 around a lot. But so far, any shifts are still within the range of its historic natural fluctuations.
But that won’t necessarily be the case for long. The researchers used climate models to simulate the jet stream in a hotter world. If the planet continues warming at a high rate, the jet stream is likely to shift north over time.
In fact, the study suggests, global warming may have already started pushing it poleward — it just hasn’t quite moved outside its normal range yet. But it could settle firmly outside its natural boundaries within 40 years.
That could cause some major weather shifts across the midlatitudes, particularly Europe.
The jet stream helps carry rainfall systems to southern Europe, which would otherwise be relatively dry. If the jet stream shifts north, it could take that rainfall with it, increasing the odds of drought.
“You’re gonna be really stressing areas that really rely on having a jet stream that exists within its natural boundaries,” Osman told E&E News.
Parts of Europe may also see an increase in floods and heat waves.
In North America, a northward-shifting jet stream may amplify warming on the East Coast and increase the severity of certain extreme weather events.
Still, Osman says, “there's reasons to be optimistic here.”
The new study used climate simulations that assume high greenhouse gas emissions and severe warming into the future. It’s a scenario that’s already relatively unlikely in the real world, as nations around the globe are striving to cut down on their carbon emissions.
Under a more moderate warming scenario — one that’s more in line with current global climate action — the jet stream is likely to shift north over time, but probably at a slower pace, Osman suggested.
“I do want to make the point that these are model scenarios of the future,” Osman cautioned. “Ultimately, its trajectory into the future is still largely within our control.”
A climate controversy
The overall position of the jet stream isn’t the only subject of interest among climate scientists.
Some experts believe climate change may also make the jet stream “wavier,” causing it to meander up and down more strongly as it flows around the world. Waves in the jet stream can also make extreme weather events worse, sometimes causing storm systems or heat waves to move more slowly or get stuck in place.
Osman’s team didn’t flag any information in their ice core analyses that would indicate a change in waviness over time. But that’s also not what their method was designed to look for, he cautioned.
At the same time, the jet stream’s position and its waviness could be related. According to James Screen, a climate scientist at the University of Exeter, some experts believe that a northward shift could result in a stronger, less wavy jet stream. A southward shift would result in the opposite.
If the jet stream does indeed shift north in the coming decades, less waviness might be expected, he said.
It’s a subject of debate among climate scientists. Some studies suggest that the jet stream is already getting wavier over time. These changes might be driven by atmospheric changes linked to rapid warming in the Arctic, some experts say.
Jennifer Francis, a climate scientist at Woodwell Climate Research Center, has devoted much of her recent career to the study of Arctic warming and large air currents like the jet stream. Some studies suggest there may be a kind of “tug of war” happening at the moment, she told E&E News. Certain effects of climate change on the atmosphere may be pushing the jet stream north, while others might be pulling it south.
Other experts aren’t convinced that Arctic warming is affecting the waviness of the jet stream at all — at least, not for the time being.
Screen, the University of Exeter scientist, has published research suggesting that any recent changes in the jet stream’s waviness are probably natural fluctuations rather than direct consequences of Arctic warming.
The subject remains a major question in climate science.
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2021. E&E News provides essential news for energy and environment professionals.