Last year brought the summer of the heatwave. As Britain baked in sunshine, the England men’s football team even managed to reach a World Cup semi-final.
But while temperatures in Britain remained just the right side of uncomfortably hot, much of Europe experienced serious extremes, in the continent’s warmest August on record. And far from being confined to the area around the Mediterranean, even Scandinavia had worryingly hot weather.
Greenhouse gas emissions from burning fossil fuels, forest destruction and other human activities are trapping heat and putting more energy into the climate system.
Hotter air means heatwaves are much more likely. For example, scientists now say the unprecedented heat and wildfires across the northern hemisphere in 2018 “could not have occurred without human-induced climate change”. In Australia, the scorching summer of 2016-17 in New South Wales was made at least 50 times more likely by global heating, linking it directly to climate change.
Hotter air can also carry more water vapour, meaning more intense rain and more flooding.
Another important factor in the northern hemisphere is the impact of changes in the Arctic. The polar region is heating more rapidly, reducing the temperature difference with lower latitudes. There is strong evidence that this is weakening the planetary waves (including the jet stream) that normally meander over Europe, Asia and North America.
When these waves stall, weather gets fixed over regions and becomes extreme. This has been linked to past floods in Pakistan, heatwaves in Russia and drought in California.
Most of the planet’s trapped heat goes into the oceans and rising sea temperatures mean more energy for hurricanes and typhoons. The deluge delivered in the US by Hurricane Harvey in 2017 was made three times more likely by climate change. Rising sea level also means storms cause more coastal damage.
Natural variability would cause some extreme weather, even without global heating, but human impacts on the climate make such extremes more likely. Carbon Brief analysed more than 230 studies and found 95% of heatwaves were made more likely or worse by climate change. For droughts, 65% were definitely affected by our hotter world, while the figure for floods was 57%.
The heatwave was part of a wider rise in temperatures across much of the northern hemisphere. Specifically, it was the result of the north Atlantic jet stream being weaker than usual, which meant the regular arrival of low-pressure systems from the west was blocked, so high-pressure systems with warm, sunny weather stayed in place for weeks on end.
At first, Europeans mostly enjoyed the heat – especially in the north, where summers can be comparatively dismal. But as time went on, with no relief from the searing sunshine, the mood changed. For the first time in decades – perhaps since the drought of 1976 – people were praying for rain. The heatwave eventually broke in early September, with unsettled weather arriving from the west.
For some, it was too late. In July, wildfires broke out along the coast south of Athens, killing more than 100 people.
