Summer heat waves driven by climate change do more than harm health and claim lives, a new study shows. They also blight national economies, and hit the poorest hardest of all.
In 21 years, soaring temperatures worldwide have fuelled an estimated US$16 trillion in economic losses, U.S. scientists have just calculated.
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And these costs are borne by the people least likely to afford them, and who have also done least to drive global heating to dangerous levels. The researchers estimate that the poorest nations in the hottest regions may have seen an economic downturn of 6.7% of gross domestic product as summer temperatures climbed between 1992 and 2013. The richest nations—Canada, the United States, and Europe, for example—may only have seen GDP losses of 1.5% during those decades.
The total economic loss is truly enormous: one calculation made just in the first six months of the COVID-19 global pandemic put the economic cost of the virus at precisely that—$16 trillion, about nine-tenths of U.S. GDP in one year.
But what a virus can do in a hurry, the burning sun can do more insidiously. And this is just the beginning.
“No one has shown an independent fingerprint for extreme heat and the intensity of that heat’s impact on economic growth,” said study co-author Justin Mankin, a geographer at Dartmouth College in New Hampshire. “The true costs of climate change are far higher than we’ve calculated so far.”
The study “shows that no place is well adapted to our current climate,” he added. “The regions with the lowest incomes globally are the ones that suffer most from these extreme heat events. As climate change increases the magnitude of extreme heat, it’s a fair expectation that those costs will continue to accumulate.”
Like all products of climate and economic models, the research arrives with careful caveats and prudent provisos. The two researchers based their study on annual temperature data and the records of the five hottest days of each year: what counts as a heat wave in Norway, however, is very different from extreme heat in Mali, or Brazil. They also concede that there are problems with the economic calculations: detailed data is always more available from the richest economies, and sometimes sketchy in the more impoverished.
But their study, in the journal Science Advances, confirms something economists have already observed: when it’s just too hot to work safely, productivity falls. During the decades in question, it dropped by at least $5 trillion and possibly as much as $29.3 trillion.
When it’s too hot in the fields, soil moisture evaporates, blooms shrivel, crops wilt, harvests dwindle, and workers stay in the shade. And such conclusions have already been repeatedly tested in the real world. Grape pickers in the vineyards of Cyprus found that temperatures as high as 36°C correlated with labour losses of up to 27%, as the soaring mercury took its toll on human metabolism and cardiovascular efficiency. The summer of 2013-2014 in Australia was the hottest ever, at a cost to the economy of $6.7 billion.
And because raw materials are part of the global traffic, heat extremes in one zone can cost economies in another. Researchers in Germany in 2016 followed 26 industry sectors—mining, textiles, forestry, quarrying, agriculture, and so on—through to sales in 186 countries to test the same evidence, and they too found that as temperatures soared, productivity fell.
And, as the latest study makes clear, the costs of climate change are not fairly or evenly shared. The world’s biggest carbon emitters such as Europe and North America are affected least, and could—in theory at any rate—even welcome some warmer summers.
“We have a situation where the people causing global warming and changes in extreme heat have more resources to be resilient to those changes, and, in some rare cases, could benefit from it,” Mankin said. “It’s a massive international wealth transfer from the poorest countries in the world to the richest countries in the world through climate change—and that transfer needs to be reversed.”