Deadly summer heatwaves are going to get worse over the next three decades, warns new research.
Carbon emissions from transport and industry are slowing down the jet stream – the ribbon of wind high up in the atmosphere that drives our weather patterns.
Scientists say that It means extreme conditions linger for longer, explaining the area of high pressure that built and built over the UK in 2018.
The joint hottest summer on record claimed around 1,000 lives in England and Wales alone during June and July.
Climate models have not taken the phenomenon into account – underestimating the the future number of droughts and floods.
An international research team found warming in the Arctic caused by the burning of fossil fuels has put the brakes on the jet stream.
This has increased the frequency of freak weather that lasts for weeks or months. Climatologists call them Quasi-Resonant Amplification (QRA) events.
Professor Michael Mann, director of the Earth System Science Centre at Penn State University in the US, said: “Most stationary jet stream disturbances will dissipate over time.
“However under certain circumstances the wave disturbance is effectively constrained by an atmospheric wave guide – something similar to the way a coaxial cable guides a television signal.
“Disturbances then cannot easily dissipate and very large amplitude swings in the jet stream north and south can remain in place as it rounds the globe.”
The jet stream is the core of strong winds some five to seven miles above the Earth’s surface that blow west to east and move weather around the globe.
In 2018 it brought flooding in Japan, record heatwaves in North America, Europe and Asia, wildfires in Greece – and even parts of the Arctic. Heat and drought in California led to the worst wildfire season ever recorded.
These underlined the impact climate change is having on extreme weather – which is no longer subtle, said Prof Mann.
He said: “It played out in real time on our television screens and newspaper headlines in the form of an unprecedented hemisphere-wide pattern of extreme floods, droughts, heat waves and wildfires. ”
Alarmingly, the devastating natural disasters will become more persistent, say the researchers.
Prof Stefan Rahmstorf, of the Potsdam Institute for Climate Impact Research (PIK) in Germany, said: “If the same weather persists for weeks on end in one region, then sunny days can turn into a serious heat wave and drought, and lasting rains can lead to flooding.”
The study, published in the journal Science Advances, found those happen when the jet stream becomes stationary – with peaks and troughs locked in place.
Climate models capture temperature change very well – but cannot accurately identify QRAs, said the researchers.
Prof Mann said: “QRA events have been shown to have a well-defined signature in terms of the latitudinal variation in temperature in the lower atmosphere.
“The change in temperature with latitude and how it responds to increasing greenhouse gas concentrations depends on physics that are well understood and well represented by the climate models.”
The researchers found the pattern of Arctic warming – called ‘Arctic Amplification’ – that slows down the jet stream also increases the frequency of floods, droughts and heatwaves.
Co-author Dr Dim Coumou, of PIK, said we do not trust climate models enough yet to predict them because they are too coarse.
As climate models are unable to capture the phenomenon of QRA they are likely underestimating how global warming will lead to them being more frequent.
If carbon dioxide continues to be added to the atmosphere they will continue to increase at the same rate they have over the past decades, said the researchers.
But if China and other countries switch to “cleaner” coal-burning methods that remove pollutants from the air – like the US and Europe have – warming of the Arctic will diminish.
It will occur because the damaging particles – especially in the mid-latitudes where there is abundant sun – cool the Earth by reflecting heat away from the planet.
Without them that area will warm – mitigating any further increase in QRAs as the difference with the Arctic drops.
By mid-century greenhouse warming once more dominates climate. Curtailing the burning of fossil fuels can prevent an increase in persistent summer weather extremes.
But the current rate of occurrence of summers like 2018 will likely persist, said the researchers.
Prof Mann added: “The future is still very much in our hands when it comes to dangerous and damaging summer weather extremes.
“It’s simply a matter of our willpower to transition quickly from fossil fuels to renewable energy.”
Among all the climate-related disasters that are confronting cities, heat waves are the deadliest.
They now cause more deaths in US cities than all other weather events combined – meaning summer death tolls will rise.
