A study has found that dangerous temperatures could kill 50% more people in Europe by the end of the century, with the lives lost to stronger heat projected to outnumber those saved from milder cold.
The researchers estimated an extra 8,000 people would die each year as a result of "suboptimal temperatures" even under the most optimistic scenario for cutting plant-heating pollution. The hottest plausible scenario they considered showed a net increase of 80,000 temperature-related deaths a year.
The findings challenge an argument popular among those who say global heating is good for society because fewer people will die from cold weather.
Pierre Masselot, a statistician at the London School of Hygiene & Tropical Medicine and lead author of the study, said they wanted to test this argument in the study: "And we show clearly that we will see a net increase in temperature-related deaths under climate change".
The study builds on previous research in which the scientists linked temperature to mortality rates for different age groups in 854 cities across Europe. They combined these with three climate scenarios that map possible changes in population structure and temperature over the century.
In all three scenarios they found uncomfortable temperatures would kill more people than they do today, but the scientists cautioned that the uncertainties in the data are large.
The net death toll is forecast to rise the most in hot southern Europe, particularly around the Mediterranean, with a second hotspot in central Europe that covers:
In cooler northern Europe, however, a small decrease in deaths is expected.
Masselot said: "In Norway, for instance, we might see a very slight benefit".
"[But this] is completely overshadowed by this massive increase we see in southern countries".
Heat and cold are silent killers that hurt the body well before they reach extremes that cause hypothermia and heatstroke. Excess deaths soar during heatwaves, particularly among people who are old or sick, as hot weather forces their bodies into overdrive and stops them from resting.
Cold spells raise blood pressure and contribute to a range of heart and lung problems.
Tim Osborn, a climate scientist at the University of East Anglia, who was not involved in the research, said: "Put bluntly, the increase in hot weather will kill more people than the decrease in cold weather will save".
"While this new study isn't the final say on the matter … it does break new ground by scrutinising people's vulnerability to extreme temperatures by age and by city to a much better level of detail than previous work".
The analysis, which was limited to European cities, did not consider rural regions which are less exposed to the urban heat island effect, or other parts of the planet where heat is a more pressing problem. In total, they estimated the high heating scenario would lead to an extra 2.3 million people dying from dangerous temperatures in Europe between 2015 and 2099.
Madeleine Thomson, a climate and health expert at the research charity Wellcome, said the death toll was just one of the dangers of rising temperatures: "Extreme heat kills but it also causes a wide range of serious health problems. It has been linked to an increased risk of cardiovascular disease, miscarriages and poor mental health".
The study explored how lives could be saved if people adapted to the changes in temperature and reduced their exposure to uncomfortable temperatures. It found that in the hottest scenario only "implausibly strong" levels of adaptation could halt the trend of rising net deaths.
In scenarios that cut carbon pollution, a 50% drop in temperature exposure was enough for new deaths to drop.
Víctor Resco de Dios, an environmental engineer at the University of Lleida, who was not involved in the study, commented: "The good news is that we can adapt".
"Adaptation starts with relatively simple solutions – although they are not free – such as installing air conditioning or creating spaces that serve as climate shelters".
"But we must also address more complex solutions – such as increasing green areas in cities to mitigate the urban heat island – and adapting health systems".
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