Fact check: How does climate change impact heatwaves?

Euronews

4 days ago

Several European countries are set to see the mercury soar again on Wednesday as high-pressure zones persist across the continent. Experts are warning that sweltering temperatures are becoming the norm.
'Extreme heat is no longer a rare event - it has become the new normal,' UN Secretary General António Guterres said earlier this week.
The abnormally high temperatures gripping Europe are caused by a heat dome, a phenomenon where high pressure lingers over a large area, trapping hot air.
But the extent to which human-induced global warming — driven by decades of fossil fuel pollution — is exacerbating such episodes of extreme heat has also come under scrutiny.
Scientists warn against directly attributing individual weather events to climate change: these episodes happen regardless.
But there is a scientific consensus that global warming is making heatwaves more frequent, intense and longer-lasting, with potentially dire consequences for people's health.
Hotter heatwaves here to stay
Researchers at Carbon Brief recently mapped every published scientific study detailing how climate change has influenced extreme weather.
This analysis covered 116 heat-related events in Europe. Of this total, scientists deemed 110 (95%) were made more severe or more likely because of climate change.
June heatwaves are around ten times more likely to occur now compared to pre-industrial times because of the impact of climate change, scientists at World Weather Attribution estimate.
Others say atmospheric events driving heatwaves have almost tripled in strength and duration since the 1950s.
Heatwaves are defined as a prolonged period — usually lasting at least three days — of higher-than-usual temperatures. This means that the threshold temperatures for a heatwave vary between countries and even within borders.
For example, temperatures need to climb to 39°C over a prolonged period in Athens for a heatwave to occur. In Helsinki, just 25°C is required for the criteria to be met.
These events happen more frequently because the mean temperature is generally higher due to climate change, making it more likely for the conditions of a heatwave to occur.
Valerio Lucarini, a climate scientist at the University of Leicester, explains that deviations from the expected weather patterns are now also much more 'persistent".
'As we have changing dynamics in the atmosphere, we have a higher probability of so-called blocked flows,' Professor Lucarini explains, referring to stationary high-pressure systems that lead to prolonged heat. 'These patterns allow for the occurrence of large temperature anomalies, and persistent ones.'
European heatwaves are potentially up to 2.5°C hotter and drier than other similar events in recent years due to human-driven climate change, according to a study led by Professor Lucarini and a group of European academics for ClimaMeter.
'We're seeing a record-breaking continental heatwave at the moment, and it's warmer than it otherwise would have been due to climate change,' Samatha Burgess, Deputy Director of the EU's Copernicus Climate Change Service, told Euronews
"This heatwave is remarkable for three reasons: the intensity of the maximum temperatures forecast over large areas, the geographical extent of the warm anomaly and how early this is in the summer period," she explained.
Burgess added that periods of extreme heat exceptionally early and late in the summertime are becoming more common, prolonging the time of the year when there are risks of severe heat stress.
Europe is particularly vulnerable
Europe is the fastest-warming continent, seeing average temperatures rise at around 0.5°C per decade compared to 0.2°C globally.
Its proximity to the Arctic, which is by far the fastest-warming part of the planet, contributes to this rapid warming, making it more vulnerable to heat waves.
Of the 30 most severe heatwaves to hit Europe between 1950 and 2023, 23 of them occurred since 2000, according to the World Meteorological Organisation's (WMO) Europe Regional Climate Centre.
Scientists also believe southern Europe and the Mediterranean are particularly exposed due to their geographical location between the dry subtropics of North Africa and the wetter parts of northern Europe.
A 2020 study concludes that this brings unusually high surface pressure over the Mediterranean Sea, as well as hot and dry air from the Sahara towards Morocco and southwestern Europe. This results in more frequent dry springs and favours summer drought and heatwaves.
Scientists also say the changing behaviour of the jet stream — the rapid currents encircling the planet from west to east — could explain why Europe and North America are increasingly exposed to heatwaves, sometimes happening concurrently.
A phenomenon known as the 'double jet stream' — where the current of air splits, leaving hot air lingering over the continent — is largely responsible for the rise in Western Europe's heatwaves, German researchers said in 2022.
What about ocean heat waves?
Land areas in Europe are warming up faster than the ocean, but the Mediterranean is currently seeing record-breaking sea surface temperatures, including for June.
'When seawater is warm, it evaporates more and heats the atmosphere above it. And with that evaporation, it generates more potential energy for storms. So there's this feedback between the atmosphere and the ocean,' Samantha Burgess explained.
Professor Lucarini pointed out that the current heatwave has coincided with a period of abnormally high temperatures — 4 to 5°C higher than average — in parts of the Mediterranean.
'We are seeing huge sea surface temperature anomalies all across the Western Mediterranean Sea and the East Atlantic,' he explained.
'Take France, it's surrounded by ultra-hot waters, so obviously, it's much more prone to having long and persistent temperature anomalies on the land, as well as very strong thunderstorms.'
Far-reaching consequences
Cold weather is estimated to cause as many as ten times more deaths in Europe than the heat. But shifting climate conditions could drive up heat-related deaths.
A study by the European Commission estimates that, without climate mitigation and adaptation, the death toll from extreme heat in the European Union and the United Kingdom could multiply thirtyfold by the end of this century.
By the same time, heat-related deaths in southern Europe are expected to be 9.3 times more frequent than in northern Europe, compared to six times more frequent now.
Extreme heat can also trigger other extreme weather events, such as subtropical storms, drought and wildfires.
"The hotter the temperature is, the more evaporation we get from soil moisture. And the drier the soil is, the drier the vegetation is above it, which means we've got a much greater risk of fires," Burgess said, adding that this "doesn't necessarily mean we'll get a fire because we still need that ignition source".
This all means Europe needs to be increasingly prepared for hot episodes and their repercussions, both from a health and public safety point of view.