By Adam Vaughan

Climate change is to blame for an average 37 per cent of heat-related deaths globally in the past three decades, according to researchers who say their finding is a reminder global warming is already having severe impacts.

Every continent saw an increase in deaths from heat linked to climate change over the period, but the percentage of heat deaths linked to climate change varied widely across the world.

The proportion was much higher in Central and South American countries including Guatemala and Colombia, and more than 50 per cent in Kuwait and Iran in the Middle East, and the Philippines in South-East Asia. The percentages were much lower in the US and Canada, and much of Europe.

“The main message is climate change is not something that will come in the future. It’s already happening, and we can quantify the negative impacts,” says Antonio Gasparrini  at the London School of Hygiene & Tropical Medicine, one of the research team.

The team took temperature and mortality data from 43 countries between 1991 and 2018, and modelled a counterfactual world without the 1.1°C of warming the world has seen to date. The difference was used to estimate the number of climate-linked heat deaths.

To account for people in different parts of the world being acclimatised to different heat extremes, the researchers tailored the risk of death from rising temperatures for all 732 locations in the study, so high temperatures in Berlin resulted in a greater increase in deaths than in Johannesburg.

Chloe Brimicombe at the University of Reading, UK, who wasn’t involved in the research, says the study is timely given the record-breaking high temperatures in some parts of the world this month. “It also shows how quicker action in the past to limit emissions would have led to fewer heat-related deaths,” she says.

However, Brimicombe believes that the study’s estimate, of 9702 deaths a year linked to heat caused by climate change, is an underestimate of the true death toll, because the research only looked at the four warmest months in each country. “Heat-related deaths have and do occur outside these months. This is especially true in the tropics where heat extremes can occur all year,” she says.

There are other reasons the real number may be higher too. Gasparrini says the big caveat to the work is that the team was were unable to source data for large parts of the world. Most of Africa and the whole of India, two of the most heat-afflicted regions on Earth, were omitted because data was unavailable.

Friederike Otto at the University of Oxford, who has studied the lack of data on heatwaves in Africa and their links to climate change, says it matters that much of the world map in the study is empty. “In most countries in the world, heatwaves are not recorded at all,” she says. “This paper shows we do not have enough data and, importantly, awareness, to quantify the impacts of climate change on lives.”

Moreover, we know worse is coming in the future: many studies have projected heat-related deaths will rise as climate change accelerates in the coming decades.

Journal reference: Nature Climate Change , DOI: 10.1038/s41558-021-01058-x

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