Sections of the planet’s jet streams have begun shifting towards the poles over the past several decades. It is most likely that this is a response to global warming due to our greenhouse gas emissions, and could exacerbate heat and drought in regions that depend on the high-altitude winds to steer storms their way.
Jet streams are bands of fast-moving winds high in the atmosphere that blow from west to east around the mid-latitudes and the poles. This is sometimes referred to as “the jet stream”, but there are separate jet streams in each hemisphere and at different latitudes and altitudes. These winds occur due to Earth’s rotation as well as the difference in temperature between the tropics and higher latitudes.
Climate models have long anticipated that global warming would cause the position of the jet streams in each hemisphere to shift towards their respective poles. This is expected to occur as increasing heat in the tropics pushes the storms that add fuel to the jet streams further from the equator. But the short satellite record of global winds has made it challenging to know if the position of the jet streams was changing with any clear trend.
Advertisement
That record, which begins around 1980, has only recently become long enough to begin reliably detecting a pattern, says at University College London. “It looks like it’s happening now – it has emerged from the noise,” he says.
He and his colleagues analysed the jet stream above the North Pacific Ocean using several datasets on wind speed in the region spanning 1980 to 2022. They found that the average position of the North Pacific Jet Stream between December and February has seen a statistically significant shift northward of around 30 to 80 kilometres per decade. Keel says the short record means it remains unclear whether this shift is greater than past variability. But using climate models, the researchers project that this shift will continue in coming decades, expanding to other months by the end of the century under a high-emissions scenario.
In another , at the University of Oxford and his colleagues took a more general look at jet streams across both hemispheres. They found that, when analysed in combination, the jet streams show a clear poleward shift in their average position between 1979 and 2019. The trend has been clearest above the Southern Ocean, where the jet stream is also influenced by the ozone hole over Antarctica. “For the other cases it’s really starting to emerge now,” says Woolings.
However, the jet streams everywhere. “There are places that it’s moving polewards, and there are places that it’s not doing anything, and there are places that are moving towards the equator,” says Keel. A related question is whether the temperature changes driving these shifts have made the jet streams “wavier”, which could lead to both more extreme cold and extreme heat events.
The exact mechanisms by which global warming influences the position of the jet streams also aren’t clear, says Woolings. But he says the observed poleward trend is probably caused by rising greenhouse gas levels: “It is certainly what we expect from climate change.”
Shifts in the position of the jet streams have an effect on global weather because they steer and create weather systems, says at the Woodwell Climate Research Center in Massachusetts. For instance, she says a shift in the North Pacific Jet Stream could exacerbate heat and drought in the western US by redirecting storms.
Other regions that are influenced by jet streams, such as the Mediterranean, Chile, South Africa and Australia, could be affected by similar shifts, says Woolings. “If you’re right on the edge of the region that gets rainfall due to the jet stream, even a degree shift of latitude could be really serious.”
Geophysical Research Letters
