July's Heat Waves "Virtually Impossible" Without Climate Change: Scientists

This summer's extreme heat in the US and southern Europe would have been "virtually impossible" without climate change, according to a rapid analysis by scientists who study how climate change influences extreme weather events.

The international scientific project World Weather Attribution found that peak heat this July - with temperatures over 45C in Mexico and the western US, southern Europe and the lowlands of China - was made more likely and more severe by human-induced climate change. In Europe and North America, the heat waves would have been almost impossible, while China's heat was made 50 times more likely by climate change.

"In the past, these events would have been extremely rare. So it would have been a huge chance, or basically impossible, that they would happen at the same time," said co-author of the report Friederike Otto, senior lecturer in climate science at the Grantham Institute for Climate Change and the Environment at Imperial College London, in a press briefing.

The return of the El Niño cycle, which warms the equatorial Pacific Ocean, plays a role in the recent heat. But the report is evidence that it can't be attributed to El Niño alone.

Intense heat has taken a toll on people's health, as well as on food, infrastructure and wildlife. The July heat has been linked to hundreds of deaths, including 211 in Mexico. Power demand for cooling and air conditioning has also spiked and crops have been affected, including olive oil in Spain and cotton in China.

World Weather Attribution specializes in near-real-time analysis linking global warming to episodes of extreme weather. Heat waves are more straightforward for scientists to study than cyclones, drought or wildfires, which involve additional complex dynamics. In previous analyses, the group found that the UK's 2022 heat wave was at least 10 times more likely because of the greenhouse gas pollution that causes climate change, and heat last spring in India and Pakistan was 30 times more likely.

The new findings are in line with previous projections by climate scientists, and show that extreme heat should no longer be seen as an unusual or notable event, the authors said. This level of heat should now be expected every 15 years in the US and Mexico, every decade in Southern Europe, and once in every five years for China.

The study, which has not been peer-reviewed but applies peer-reviewed methods used in other studies measuring the impact of climate change on weather events, also found that this summer heat waves would have been significantly milder without climate change. Temperatures would have been 2.5C cooler in southern Europe, 2C cooler in North America and 1C cooler in China. If global warming increases to 2C above pre-industrial levels, such severe heat is expected every two to five years in these regions, the authors said.

"As long as we keep burning fossil fuels we will see more and more of these extremes," Otto said. "[T]he most important thing is that they kill people, and they particularly kill and hurt and destroy the lives and livelihoods of those most vulnerable."