The polar jet stream is a wind band that separates cold Arctic air from warmer air to the south.
A new study suggests that as the Earth warms, this band is moving north and out of position.
That could lead to more droughts and heat waves in southern Europe and the eastern US.
The polar jet stream orbits the Northern Hemisphere, swirling up to nine miles above our heads like a sinuous, ethereal crown of the planet.
This band of strong winds separates cold air from the Arctic from warmer air to the south and is responsible for transporting weather from west to east across the US, across the Atlantic and into Europe. It determines how wet and warm these regions are.
But according to a recent study, the jet stream shifts north as global temperatures rise. That’s because the delicate balance of warm and cold air that holds the flow in place is disrupted. If greenhouse gas emissions continue unabated, the study found, the jet stream will move out of its normal range by 2060.
“The ‘beginning’ of the jetstream’s northward migration may have already begun,” Matthew Osman, a researcher at the University of Arizona’s Climate Systems Center who co-authored the study, told Insider.
That would wreak havoc on the weather in the Northern Hemisphere, bringing more extreme events such as droughts and heatwaves to southern Europe and the eastern US. More rain and flooding are expected in northern parts of Europe and Scandinavia, Osman said.
A migrating jet stream
The North Atlantic jet stream exists and is held in place thanks to the collision between warm air zooming north from the tropics and cold air in the Arctic. Once these air masses meet, they move eastward at 110 miles per hour, propelled by the Earth’s rotation.
But rising air temperatures mess with that crowds. The Arctic is warming on average twice as fast as the rest of the planet. So that warm air travels farther north before it finds cold air, prompting the position of the jet stream to migrate to higher latitudes.
Osman noted that the jet stream is erratic; the tire’s location is constantly shifting as the temperature difference it causes fluctuates. But his study took a longer look and examined the location of the stream over the past 1,250 years. To reconstruct that past behavior, the researchers looked at ice core samples from 50 sites on the Greenland ice sheet dating back to the 8th century. The cores revealed how much snow had fallen, and when.
Then, using climate models, the team simulated where the jet stream could move over the next four decades if greenhouse gas emissions continue at their current rate. The results showed that the current movement of the wind band threatens to surpass any previous shift.
It is expected to deviate significantly from the norm, with potentially devastating consequences.
“By pushing the jet stream beyond its already great natural range, we could expose ourselves to increasingly severe climate risks in the future,” Osman said.
There could be more droughts and floods
Osman’s study suggests that the jetstream migration will likely cause the US East Coast to warm faster than it already is. And both North America and Europe will experience more droughts and heat waves.
“Europe, at the downstream end of the North Atlantic jet, will feel these effects most acutely,” Osman said.
In particular, the semi-arid regions of southern Europe could become drier. Parts of northern Europe that already have wetter, milder climates, such as Scandinavia, could get even wetter. That extra rainfall would lead to more flooding like the one that ravaged Europe this summer.
Changes in the jet stream can also affect polar vortices
Some scientists believe that warming will also make the jet stream more wavy than it already is.
The path of the jet stream is meandering and sinusoidal because not all warm air moves north at the same speed, nor does all polar air move south uniformly. Hence the many waves in the wind orchestra.
But one study published last month suggests that melting Arctic sea ice could increase the intensity and size of those anomalous bulges. When that sea ice melts, more heat and moisture move from the Earth’s surface to space. That acts like a rock thrown into the pond of the atmosphere — it creates strong ripples over the Arctic that distort the jet stream. This creates squiggles that push extraordinarily cold air toward the equator.
So a more wobbly jet stream consequently increases the likelihood of intense winter storms and cold showers in the US. Examples of this extreme winter weather are: the polar vortex event that hit the US in 2019 and the winter storm that left millions of Texans without power in February.
“If the undulation of the jet stream increases in the future, it could mean that extreme events like the polar vortex could also become more frequent,” Osman said.
Read the original article Business Insider