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 (5 Fahrenheit) beyond pre-industrial levels by 2100, people under 35 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 with 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 and 2019.

In contrast, more older people accounted for cold-weather mortality events.

Looking ahead to a scenario when the global population and carbon emissions continue growing, the researchers projected a 32% increase in temperature-related deaths in those aged under 35 would occur by 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.

How hot is too hot? It's probably cooler than you think

Wilson's group also found the amount of heat exposure that could lead to 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 said in some cases, limits could actually be in the mid 20s. 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.

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 front line of a warming world.

Experts say 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," he added.

Such conditions have long been forecast, given the pace at which carbon emissions have increased in recent years. The world has already temporarily breached the 1.5-degree Celsius lower threshold set in the Paris Climate Agreement.

In 2017, studies anticipated as much as 70% of India's population could be exposed to unlivable heat by 2100.

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