The burden of heat-related death could shift from the elderly to young people by century's end, according to a new study.
In a future scenario that sees average global temperatures go at least 2.8 degrees Celsius beyond pre-industrial levels by 2100, people under 35 years would likely suffer the effects of a warming world more than older adults.
The analysis, published in the journal Science Advances, inspected mortality data from Mexico.
The data enabled the researchers to take age and dates of death, compare it to the environmental conditions, and calculate how often humid heat exposure resulted in premature death.
Scientists have long thought that excessive heat in a warming climate would have a higher impact on older populations.
Surprisingly, it appears to be a silent killer of young people in certain climates.
Extreme heat a silent killer of young people
According to the study, three out of four heat-related deaths in Mexico occurred in people aged under 35 between 1998-2019.
In contrast, more older people accounted for cold-weather mortality events.
Looking forward to a scenario when global population and carbon emissions continue growing, the researchers projected a 32% increase in temperature-related deaths in those aged under 35 years would occur by the year 2100.
A near identical decrease in mortality rates was seen in older groups.
The explanation for why younger people may be shouldering more heat-related deaths than anticipated likely comes down to social reasons.
Younger people may be more likely to find themselves exposed to heat outdoors, while a warming climate could cut cold-related impacts on their elders.
"Younger people have higher activity levels, they are more likely to be exposed to heat in outdoor work environments," study leader Andrew Wilson from the Center on Food Security and the Environment at Stanford University told DW.
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Wilson's group also found the amount of heat-exposure required for death is lower than scientific literature suggests.
Many environmental variables, including air temperature and humidity, are used to indicate heat stress. These are sometimes called "real feel" or "wet bulb” temperatures.
Older studies put a temperature limit for human heat stress at 35 degrees Celsius (95 degrees Fahrenheit).
Prolonged exposure to this 35-degree wet bulb limit theoretically means the body would be unable to cool its core temperature, resulting in heat-related death.
But this limit was calculated in lab conditions where a person would be resting in the shade, in gale-force winds, doused in water, and naked — hardly a realistic scenario.
Wilson says in some cases, limits could actually be in the mid 20's. Studies like his have since tried to account for real world conditions.
"We find even in the mid-20 [degrees Celsius], there's already quite a bit of mortality, especially for the youngest people," Wilson said.
"That's probably because they're moving … working outdoors … they're in the sun.”
Simply put: a hot day, is a hot day, and it takes its toll on people's bodies.
Men sit and stand under tree shade on a hot day near a work site.
Outdoor workers in Kuwait take shelter during a 2022 heat wave.Image: Yasser al-Zayyat/AFP
Heat-related deaths a global issue
While the study only looks at Mexican health data, it provides a concerning glimpse at a potential future for other nations on the frontline of a warming world.
Experts say that mortality is a huge part of the cost of climate change.
"We think many fewer people will die from cold, many more people will die from heat. We think most of those additional deaths from heat are going to happen in low- and middle-income countries," Wilson said.
"Most of the reduction in cold-related deaths will be in Europe and North America, right? So this is already an inequality picture," Wilson added.
Such conditions have long been forecast, given the pace at which carbon emissions have increased in recent years. Already the world has temporarily breached the 1.5-degree Celsius lower threshold set in the Paris Climate Agreement.
In 2017, studies anticipated as much as 70 percent of India's population could be exposed to unlivable heat.
And in recent years, Middle East nations have introduced work bans to counter extreme heat conditions.
Edited by: Fred Schwaller
Sources:
Heat disproportionately kills young people. Published by Andrew Wilson et al. in Science Advances https://www.science.org/doi/10.1126/sciadv.adq3367
An adaptability limit to climate change due to heat stress. Published by Steven C. Sherwood and Matthew Huber in PNAS www.pnas.org/cgi/doi/10.1073/pnas.0913352107