Global warming already responsible for one in three heat-related deaths

Adapted from a media release from the London School of Hygiene & Tropical Medicine and the University of Bern.

Head of our Climate, Air Quality Research Unit, Professor Yuming Guo, has collaborated with international colleagues on a major study which shows for the first time the actual contribution of man-made climate change in increasing mortality risks due to heat. Led by the University of Bern and the London School of Hygiene & Tropical Medicine, the study found that between 1991 and 2018, more than a third of all deaths in which heat played a role were attributable to global warming. The study, the largest of this kind, used data from 732 cities in 43 countries around the world and has just been published in Nature Climate Change.

Global warming has many potential health impacts, and morbidity and mortality data can reveal these. Many models predict a substantial rise in average temperatures, and in the occurrence of extreme events such as heatwaves, which could increase related health burdens.

Until now, no study has evaluated if, and to what extent, these health impacts have already been experienced in recent decades. This study shows that 37 percent of heat-related deaths globally between 1991 and 2018 can be attributed to changes in climate that are related to human activities.

Across Brisbane, Melbourne and Sydney, the 5,539 recorded heat-related deaths between 1991-2018 accounted for 1.78 percent of all warm-season deaths in that period. 35.7 percent of those were attributable to human-induced climate change. Of all deaths occurring during warm seasons in that period, 2,968 or 0.63 percent were specifically attributable to human-induced climate change.

The researchers analyzed man-made global warming, in a so-called "detection & attribution" study that identifies and attributes illness and deaths to changes in climate and weather. Specifically, the researchers projected past weather conditions, investigating what would occur under scenarios with and without emissions caused by human activity.

Lead researcher Dr Ana M. Vicedo-Cabrera says, "We expect the proportion of heat-related deaths to continue to grow if we don't do something about climate change or adapt our health services. So far, the average global temperature has only increased by about 1°C, which is a fraction of what we could face if emissions continue to grow unchecked."

While on average over a third of heat-related deaths are due to human-induced climate change, impact varies substantially across regions. The number of climate-related heat casualties ranges from a few dozen to several hundred deaths each year, depending on the local changes in climate in each area and the vulnerability of its population.

Populations living in low- and middle-income countries, which have been responsible only for a small part of human-caused emissions in the past, are those most affected, with the proportion of human-induced heat-related mortality higher in Central and South America and South-East Asia.

“This is the largest detection & attribution study on current health risks of climate change,” says Prof Antonio Gasparrini, the senior author of the article. “The message is clear: climate change will not just have devastating impacts in the future, but we are already experiencing the dire consequences of human activities on our planet”.

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