Western Europe’s second record-shattering heat wave in two months aligns with a grim trend: For the past three decades, Europe has been warming faster than any other continent.
Average temperatures there have climbed by roughly 1 degree Fahrenheit (0.56 degrees Celsius) per decade since the mid-1990s, more than double the pace of warming worldwide, according to Copernicus, the European Union’s climate-monitoring service.
Emissions of carbon dioxide and other heat-trapping gases from human activity are driving the planet’s long-term increase in temperatures, which is helping hot spells reach ever-greater extremes of severity and duration.
But local factors determine how all that excess heat is distributed around the world and why temperatures are rising faster in some places than others.
In Europe’s far-northern reaches, for instance, the warmer atmosphere is melting the sea ice that once covered huge swaths of the Arctic. That leaves more of the ocean’s bare, dark surface to absorb the sun’s energy, exacerbating warming in and around the top of the globe.
Pollution controls are another factor behind how quickly Europe has heated up. Curbs on industrial emissions have been good for Europeans’ lungs but have also left fewer particles in the air called aerosols that can bounce solar radiation back into space.
There’s also less snow on the ground to deflect the sun’s energy. Last year, the amount of ground covered by snow in Europe was, at its annual peak, about a third below average, according to Copernicus. The result is more exposed soil that can take up heat, especially in Scandinavia and the European part of Russia.
These changes on land and at sea are also modifying the way air moves above Europe, in ways that could be making searing heat waves more frequent.
The temperature difference between the hot equator and the cold North Pole is a major driver of weather throughout the Northern Hemisphere. But when there’s less snow on the ground in Europe each spring and less ice offshore, that temperature gap shrinks. This might be redirecting the jet stream, or the belt of strong westerly winds that steers the weather, in ways that produce prolonged summer heat waves on the Continent, scientists showed in a 2020 study.
In recent decades, the jet stream has also been splitting more often into two branches over Europe, creating an area of weak winds where heat can become trapped for days, scientists have found.
Normally, the jet stream keeps cool maritime air blowing into Europe from the Atlantic. But when the jet splits, the high-pressure air in between the two branches reroutes this normal movement of weather fronts. That can transform what might otherwise be just a few sweltering summer days into a weekslong heat wave, with deadly consequences.
In a 2022 study, researchers found that almost all of the recent increase in the frequency and intensity of heat waves in Western Europe was linked to these “double jet” patterns sticking around for longer stretches. Whether human-caused changes in the climate are making double jets more persistent or frequent is still uncertain, though.
In the 2003 heat wave that killed as many as 70,000 people across Europe, the double jet lingered for 29 days. Even if the current heat doesn’t prove as long-lasting, it is already rewriting the record books — not by modest increments but by big jumps.
Scientists are analyzing the current temperatures in France, Britain and other places to estimate how much more likely a heat wave of this magnitude has become as a result of human-caused warming.
“We expect increasing temperatures and the breaking of temperature records due to climate change,” said Lizzie Kendon, a climate scientist at the University of Bristol in England. What’s been “extraordinary” during this heat wave, she said, are the margins by which previous records are being surpassed.
This article originally appeared in The New York Times.
