Jet streams and heatwaves: what's the link?

Jet streams – strong winds above the Earth – are fuelling the increasing number of heatwaves the world is experiencing, scientists say. And evidence suggests the jet-stream changes of behaviour are linked to warming temperatures in the Arctic.

Jet streams live in the upper parts of the atmosphere and are relatively narrow bands of strong wind, the US National Weather Service explains.

The jet streams blow from east to west and are formed at the boundaries between hot air towards the Earth’s equator and cold air towards the north and south poles.

Changes in the jet stream, like its shape and speed, can cause changes in the weather system below it.

The Met Office, the UK’s national meteorological service, compares the jet stream to a vacuum cleaner five to seven miles above the Earth’s surface. It can suck air out of the weather system, lowering pressure and causing stormy weather.

If the jet stream buckles and slows, on the other hand, it can lead to high pressure and drier weather.

Scientists believe the recent global heatwaves are linked to a strange pattern in the jet stream that has been called “wavenumber 5”, according to the Financial Times.

When the jet stream forms into a U-bend shape, it can generate heatwaves.

Five of these U-bends – which are called ‘omega blocks’ because they look like the Greek letter omega – are currently circling the world in a pattern.

This pattern is what scientists are calling wavenumber 5, and the FT reports that it “can persist for weeks, causing hot areas to stay hot for a long time”.

Heatwaves have “scorched” Europe, North Africa, the Middle East and Asia in June and July 2022. NASA’s Earth Observatory says temperatures have soared above 40 degrees Celsius in places and have broken many records.

Western Europe was already experiencing serious drought and was particularly badly affected, with fires across Spain, Portugal and parts of France.

A study in Germany links Europe’s heatwaves to changes in the jet stream. Scientists say a form of double jet stream, when the band of wind splits into two, is responsible for almost all of the rise in Western Europe’s heatwaves, and about a third of the increased heatwaves over Europe as a whole.

The study, published in the journal Nature, links the double jet streams to “much warmer” land areas in the Arctic.

This warmer land increases the temperature contrast with the cooler Arctic ocean, and this could trigger the clash that leads to double jet streams.

New data shows the Arctic is heating up seven times faster than the global average - at between 2.7C and 4C a decade. Global warming – caused by emissions of greenhouse gases like CO2 – is linked to rising temperatures in the Arctic.

More research and climate modelling is needed, the scientists say.

If current climate models aren’t updated, it could lead to future heatwave trends over western Europe being “significantly underestimated”, they warn.