Are heatwaves evidence that climate change is speeding up?
run of very hot days should happen in July is, by itself, perhaps unsurprising. Two-thirds of the Earth’s land is in the northern hemisphere, and land warms up faster than water does, so northern summers are the hottest times of year for the planet as a whole. But the highest temperatures tend to come later in the season.
That this year’s should start so early, rise so high and run so long is unprecedented. So is what is happening in the oceans (see chart). Since March 13th the sea-surface temperature in low- and mid-latitudes has been higher than on the same day in any year since 1979.
Normally highest in the southern summer (most of Earth’s water is in the south), temperatures are at record levels in the southern winter. Within the rising global averages lie savage peaks in particular places. On July 16th a site in the Turpan Depression in Xinjiang, sometimes called China’s Death Valley, reported a high of 52.2°C.
In America, in Death Valley proper, the same day saw a peak of 53.9°C. Of more immediate concern than isolated spikes in deserts, temperatures have been dangerously high in places where hundreds of millions of people live, too. On July 6th, after the city measured its highest July temperature ever, authorities in Beijing announced their second red alert for heat in two weeks.
July 19th marked the 19th day in a row that the temperature in Phoenix, Arizona, has exceeded 43°C. Things are similarly sweltering in Italy and many nearby countries (see map). Asked how such a thing might be, one climate scientist replies drily “I suspect it might have something to do with accumulation of greenhouse gases in the atmosphere." More greenhouse gas in the atmosphere results in more of the warmth from the sun being trapped
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