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The heatwaves that hit North America and Europe in July would have been “virtually impossible without climate change”, said researchers who stressed that extreme weather events would occur with greater frequency.
The World Weather Attribution research group, an academic collaboration, added that human-induced warming made the recent extreme heat in China “at least 50 times more likely”.
Events like the simultaneous and record-breaking temperatures in July could now be expected roughly “once every 15 years in North America, about once every 10 years in southern Europe and approximately once every five years in China”, WWA said in a report on Tuesday. The group found that about 75 per cent of extreme weather events it had recently assessed were made more likely or severe by climate change.
If the world warmed by 2C above pre-industrial levels, “events like [the recent heatwaves] will become even more frequent, occurring every two-five years”, the team of six researchers from the UK and the Netherlands said.
The 2016 Paris Agreement commits countries to strive to limit warming to 1.5C above pre-industrial levels. However, the world has already warmed by at least 1.1C, and current climate pledges set it on track for a temperature rise of between 2.4C and 2.6C by 2100, according to the UN.
“The result of this attribution study is not surprising,” said Friederike Otto, senior lecturer in climate science at the Grantham Institute for Climate Change and the Environment and an author of the report. “The world hasn’t stopped burning fossil fuels, the climate continues to warm and heatwaves continue to become more extreme.”
Scientists are clear that extreme weather events, including heatwaves, will become more frequent and intense with every fraction of a degree of warming.
The WWA, which assesses the impact of climate change on weather-related disasters including floods, fires and heatwaves, found in 38 out of its 52 studies that the events were made more likely or severe by warming.
Following the hottest June on record globally, large swaths of the US, Mexico, Europe and China experienced extreme heat in July. The World Meteorological Organization said preliminary data indicated that the start of July was the “hottest week on record”.
Temperatures exceeded 50C in Death Valley in California, while record highs were also hit in parts of China and Europe. Heat-related deaths have been reported in countries including the US, Mexico and Italy, and wildfires have broken out in parts of Greece, leading to the evacuation of tourists on some islands such as Corfu and Rhodes.
The WWA said heatwaves were no longer rare, but that without anthropogenic or man-made warming they would have been “extremely rare”.
The recent heatwaves were around 2.5C warmer in southern Europe than they would have been without climate change, 2C warmer in North America and 1C warmer in China, the WWA found.
“Unless the world rapidly stops burning fossil fuels, these events will become even more common and the world will experience heatwaves that are even hotter and longer-lasting,” the researchers said.
The scientists analysed data and computer model simulations to compare today’s climate with past weather patterns.
They looked at the average maximum temperatures over seven days in southern Europe, over 18 days over the western US, Texas and northern Mexico, and over 14 days over the lowlands of China — when the heat was at its most dangerous levels in each region.
