The heatwaves scorching parts of North America, southern Europe and China would have been cooler and far less likely without climate change, an has found.
From Death Valley, California, to northern Spain and China, the past two months have seen record-breaking heat across the northern hemisphere, putting millions of people at risk of heat-related illness and sending energy demand soaring as people crank the air conditioning. Global average temperatures made June the hottest month on record, and July is shaping up to be even hotter in what may well become the hottest year on record.
But none of this should be a surprise with climate change, says at Imperial College London. 鈥淪uch events are not rare in today鈥檚 climate,鈥� she says.
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To understand the role of climate change in driving the heat, Otto and her colleagues analysed average maximum temperatures in three regions: southern Europe, the US Southwest and northern Mexico, and the lowlands of China鈥檚 east and north. They compared these with temperatures in those regions projected by climate models that exclude the influence of human-caused global warming.
They found the heatwaves in North America and Europe were made at least 1000 times more likely by climate change. The heatwave in China had a higher chance of being due to natural variability, but the researchers found that climate change made it around 50 times more likely.
What would have been rare or impossible without climate change is now almost commonplace, says Otto. She and her colleagues found the heat in North America could be expected once every 15 years, while the heat in southern Europe could be anticipated once every 10 years and the heat in China could occur once every five years.
The researchers also found climate change made the heatwaves hotter. Compared with an equally likely heatwave in a world without climate change, the heat was 2.5掳C warmer in Europe, 2掳C warmer in North America and about 1掳C warmer in China. In all regions, they found future warming would make similar events both more frequent and more intense.
鈥淚t shows just how much climate change plays a role in what we鈥檙e experiencing,鈥� says Otto. She also says the potentially historic El Ni帽o climate pattern聽developing in the Pacific Ocean has not yet played an appreciable role in the heat.
Rapid attribution studies like this are commonly used to assess the links between particular weather events and climate change, whether extreme heat or hurricanes. at the University of Exeter in the UK says the group鈥檚 methods are well established and the results are consistent with what we know about climate change.
at Texas A&M University says the study is robust, but points out that the contribution of climate change to particular temperature extremes will be more significant when considering average temperatures across large regions. Local maximums are more likely to be influenced by natural variability.
