Why climate scientists are struggling to explain Europe’s extreme summer
A succession of heatwaves, record-breaking temperatures and unusually warm nights has swept Europe during the summer of 2026, offering a stark example of how climate change is reshaping weather patterns.
France alone has experienced five heatwaves this summer, with temperatures rising above 40C in several areas and records repeatedly broken across the country and elsewhere in Western Europe.
Scientists say climate change is clearly making extreme heat more intense. But one feature of this summer remains harder to explain – the repeated return of heat, with prolonged hot spells leaving little time for people, ecosystems or infrastructure to recover.
Repeated extremes
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“What climate change does is put heatwaves on steroids,” Robin Noyelle, a climatologist at ETH Zurich, the Swiss Federal Institute of Technology, told RFI.
“Since summers are becoming hotter on average, when we have an extreme event above the average, that extreme is even more intense than before.”
The mechanisms behind individual heatwaves are relatively well understood. Persistent high-pressure systems can become stuck over a region, allowing warm air to sink while clear skies let solar radiation heat the ground and lower atmosphere.
“If we look at heatwaves one by one, there's nothing particularly exceptional about them,” Noyelle said.
“What's happening is that we have a high-pressure system that becomes stationary over a particular region and doesn't move. So we have warm air sinking, and on top of that, the energy from the sun isn't reflected by the clouds and therefore reaches the lower layers directly. And the lower atmosphere is where we live.”
What is more unusual in 2026, however, is how often those conditions have returned.
“What we don't understand very well – and what's truly exceptional about this summer – is the fact that it's happening again,” he said.
Researchers are still exploring the reasons.
One possibility, Noyelle said, is simply chance – an unusual sequence of atmospheric conditions during the same summer.
Another hypothesis involves ocean conditions, including the exceptionally strong El Nino event observed this year.
“We have the El Nino event, which is the strongest we've ever observed since at least the end of the 19th century,” he said. “And perhaps there could be a link.”
But he cautioned that scientists have not yet reached a consensus.
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Broader trend
That uncertainty does not change the broader trend. Climate change is raising average temperatures, creating a warmer baseline from which extreme heat develops.
Nor does an exceptional summer such as 2026 mean every future year will be hotter than the last.
The climate varies considerably from year to year and cooler, wetter summers can still occur.
“Given that this year really is an exceptional summer, I don't think I'm going too far in saying that future summers will probably be cooler,” Noyelle said.
Over the longer term, however, the direction is clearer.
“Looking 20 or 30 years ahead, if we continue to emit greenhouse gases, we'll keep heading in that direction,” he said.
“A summer like that of 2026 will no longer be exceptional as it is this year; it will be average.”
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Small rises, big impacts
The succession of temperatures above 40C can make the Paris climate agreement's target of limiting global warming to 2C seem surprisingly modest.
But the figure refers to the increase in the global average temperature, rather than the temperatures people experience locally during heatwaves.
“2C doesn't seem like much,” Noyelle acknowledged.
“In fact, the global temperature is very different from the temperature we actually experience.”
Warming is not evenly distributed around the planet. Land areas generally heat faster than the global average, while warming is amplified further at higher latitudes.
According to Noyelle, a global temperature increase of between 1.5C and 2C could correspond to warming over land that is around 50 percent greater.
For France, global warming of 2C could translate into an average summer temperature increase of roughly 4C.
Extreme temperatures could rise even further.
“When it comes to extremes, we could see an amplification of up to a factor of two compared to that,” he said.
That could mean the hottest conditions becoming around 8C warmer than they once were.
The difference between averages and extremes is crucial to understanding what climate targets mean in practice. A relatively small increase in the global average can translate into more dramatic changes during the hottest days of the year.
This summer's relentless heat should not be seen as a precise preview of every summer to come. Cooler years and seasonal variations will still occur.
But climate science points to a clear long-term trend: without major cuts in greenhouse gas emissions, summers that are considered extraordinary today could become increasingly ordinary within a few decades.
This article has been adapted from the original version in French by RFI's Florent Guignard