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Scientists said “heat domes” and related atmospheric events behind extreme weather around the world this week had almost tripled in strength and duration since the 1950s, as tens of millions of people sweltered in “dangerous heat” in parts of the US and Europe.
Temperatures passed 40C in parts of the US as a so-called heat dome — a phenomenon that occurs when a high-pressure system traps heat — took hold across eastern and central states. In Manhattan, temperatures hit 99F (37C) and John F Kennedy airport reached 102F (38.9C).
Countries including Greece, Spain and France have also faced heatwaves this month due to another heat dome having formed over part of Europe, while areas of China have been hit with severe flooding.
Even as London Climate Action Week convened, with more than 700 events taking place, the capital experienced unusually warm temperatures combined with humidity.
The UK Met Office said higher temperatures were likely to build over the weekend and into early next week, particularly in south-east England and east Wales, where peak temperatures of as much as 34C on Monday have been forecast.
“This, in part, will be influenced by a heatwave developing across western Europe,” said Mike Silverstone, deputy chief meteorologist at the Met Office. “By the weekend, an area of high pressure will be intensifying and dominating the UK forecast.”
The UK Health Security Agency has issued amber and yellow heat-health alerts for much of England from Friday until Monday.
“Dual heat domes” in both Europe and North America were likely to “become more common as we continue to heat the planet”, said Michael Mann, professor at the Department of Earth and Environmental Science at the University of Pennsylvania.
Research by Mann and colleagues, published in the journal Proceedings of the National Academy of Sciences, found that the amplification of waves in the jet stream — the fast-moving band of air encircling the planet — had led to a dramatic increase in atmospheric events, driving heatwaves, wildfires and floods.
The phenomenon, known as quasi-resonant amplification, causes low- and high-pressure weather systems to linger over a region for longer periods.
The study of the jet stream behaviour calculated the number of quasi-resonant amplification episodes within each year.
Using seven decades of data, a trend emerged in the annual count of events during the summer in the boreal region, or the northern climatic zone south of the Arctic, where the jet stream encircles the globe.
This corresponded to roughly a tripling from approximately one event per year to about three events a year when calculated over the past 70 years.
The present “dual heat domes show that this was part of a very large-scale pattern”, which was linked to a “very wiggly jet stream where the ‘wiggles’ stay in place for days on end”, said Mann.
Existing climate models were “not entirely capturing the phenomenon and how it is impacted by human-caused warming”, Mann said.
The US National Weather Service said midweek that the “extremely dangerous heat” would persist across the US midwest and east coast before moderating by the end of the week.
The risk of excessive rainfall and severe thunderstorms was higher in other areas, with warnings of flash flooding in New Mexico and Texas.
“This level of heat is dangerous to anyone without effective cooling and/or adequate hydration. Heat-related illnesses increase significantly during extreme longer duration heat,” the NWS noted.
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