More than 50 degrees in Death Valley in the United States, a historic record of 45.3 ° C in Catalonia, more than 43 ° C in Phoenix for 24 days: without climate change, such heat waves would have been “virtually impossible” in Europe and the United States, shows Tuesday the World Weather Attribution (WWA) network.
This scientific network, which assesses the link between extreme weather events and climate change, also believes that the latter has made the heat wave in China “at least 50 times more likely”.
Climate change, caused by human-caused greenhouse gas emissions, “has made heat waves hotter, longer and more frequent,” says the WWA.
“Recent heat waves are no longer exceptional events” and those that will occur “will be even more intense and more common if emissions are not reduced quickly”, conclude the researchers.
Because if natural phenomena such as anticyclones or El Niño can contribute to triggering these heat waves, “warming up the temperatures of the planet by burning fossil fuels is the main reason why they are so serious”, underlines the WWA.
2.5°C warmer
To reach these conclusions, the study’s authors — seven Dutch, British and American scientists — relied on historical weather data and climate models to compare today’s climate and its global warming of 1.2 degrees with what it was in the past.
These results, produced on an emergency basis, are published without going through the long process of peer-reviewed journals, but combine methods approved by their peers.
The scientists particularly focused on the periods when the heat was “the most dangerous”, i.e. from July 12 to 18 in southern Europe, from July 1er through July 18 in the western United States, Texas, and northern Mexico, and July 5 through July 18 in central and eastern China.
They recalled that global warming worsens the intensity of temperatures: with it, heat waves in Europe are 2.5°C warmer, those in North America increase by 2°C and those in China by 1°C, indicates the WWA.
July 2023 is “on track to become the hottest July ever measured”, according to NASA and the European observatory Copernicus.
“In the past, such events would have been aberrant. But in today’s climate, they can now reproduce approximately every 15 years in North America, every 10 years in southern Europe and every 5 years in China,” said Mariam Zachariah, a scientist at Imperial College London, who contributed to the study.
“Boring”
These heat waves “will become even more frequent and will occur every two to five years” if global warming reaches 2 degrees, “which could happen in about 30 years, unless all the signatory countries of the Paris Agreement fully implement their current commitments to rapidly reduce their emissions”, she added.
This beginning of summer “could become the norm […] and even be considered fresh if we do not achieve carbon neutrality”, underlines the British climatologist Friederike Otto.
For her, “the results of this attribution study are not a surprise. […] From a scientific point of view, it is even boring because it only confirms what we had expected. But what we did not foresee is how vulnerable we are to the effects of global warming. Because it kills people, ”she said.
However, “these heat waves are not proof of a ‘warming runaway’ or a ‘climate collapse’. We still have time” to reverse things, says the scientist.
“There is an urgent need to stop burning fossil fuels and work to reduce our vulnerabilities. If we don’t, tens of thousands of people will continue to die,” said Ms.me Otto, deeming “absolutely essential” the adoption of international legislation on the phasing out of fossils during the 28e UN climate conference in November in Dubai.