Arctic climate

Siberia’s heatwave would not have happened without climate change

Few extreme weather events can be wholly pinned on greenhouse-gas emissions. This one can

THIS HAS been a sweltering year in the Siberian Arctic. Between January and June, temperatures across the region were more than 5°C warmer than the recent average (calculated between 1981 and 2010). In some spots they were more than 10°C above average. On June 20th in the town of Verkhoyansk in north-eastern Siberia thermometers read 38°C—the highest ever recorded north of the Arctic circle, according to Russia’s meteorological service.

This extraordinary heatwave has drawn the attention of the World Weather Attribution (WWA) project, a collaboration among climate researchers who specialise in quantifying the role that climate change plays in extreme-weather events (such as particularly large and devastating floods, droughts or cyclones, as well as heatwaves). Such events occurred even before modern industries began churning out large quantities of greenhouse gases. But the resulting warming of global temperatures can make extreme weather likelier or more severe.

The quantification method involves repeated simulations of the climate with and without historical emissions; researchers then estimate how the odds of a specific extreme-weather event vary in each scenario. In the past, such studies have shown that specific events were made somewhat more likely by greenhouse-gas emissions, or not at all. In 2019, for instance, an analysis found that a heatwave then besetting Europe was at least five times more likely in a world with anthropogenic climate change than in one without it.

In recent weeks, the WWA has been running a similar experiment on the Arctic. Their results, announced on July 15th, are remarkable. With “lower confidence” they conclude that the record-breaking temperatures in Verkhoyansk were made many thousand times likelier by climate change. But the researchers say “with high confidence” that global warming made the January-to-June heatwave at least 600 times more likely. The temperatures “would have been effectively impossible without climate change”, says Andrew Ciavarella, of Britain’s Met Office, a member of the modelling team. "We wouldn't expect the natural world without warming greenhouse gases to generate six-month average temperatures like this in anything less than once in every 80,000 years or so."

The increased likelihood is several orders of magnitude greater than such studies normally find. Friederike Otto, a climatologist at Oxford University who leads the WWA initiative, can think of just one other study that came to a similar conclusion. In that case, attribution modelling found that extremely hot days recorded in Japan in 2018 had been essentially impossible without climate change.

This year’s Arctic heatwave has had far-reaching consequences. The layer of ice that floats at the surface of the Arctic Ocean always shrinks in the summer before growing again during the cold and dark winter months. But the latest satellite data show that it covered 10.58m square kilometres in June, the third-smallest area on record for that month. In the Laptev Sea, north of Siberia, sea ice has been at a record low for this time of year.

On land, the heatwave has encouraged widespread wildfires across the region. They began particularly early in the season and may have been left-overs from the fires that scorched the region in 2019, generating slow underground burns that could have lasted all winter. Frozen soils, known as permafrost, are also melting fast. On May 29th a diesel storage tank near the city of Norilsk collapsed when the ground gave way beneath it, pouring 21,000 tonnes of fuel into surrounding waterways.

Sadly, all this is in keeping with climate trends for Earth’s northernmost region. The Arctic is warming on average twice as fast as the rest of the planet, because of positive feedback mechanisms that amplify local warming. According to other research published last week, the warming will continue for decades, no matter how far or fast emissions are cut, making it imperative that Arctic nations prepare for more hot summers. Perhaps the only small comfort to be drawn is that warmer temperatures may provide a boost to soil bacteria that like to munch on carbohydrates. This might at least help to clean up some of the diesel.

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