Extreme heat is associated with far more than the familiar risks of dehydration and heatstroke. New research suggests that soaring temperatures may be linked to a much broader range of health problems, including skin conditions, kidney dysfunction, traffic accidents and changes in human behavior.
At the same time, hundreds of millions of children worldwide are exposed every year to dangerous levels of heat stress associated with human-driven climate change.
The findings come from two studies published in Science Advances, highlighting the increasingly diverse health consequences of a warming planet.
Heat linked to dozens of health conditions
Tracking the health effects of extreme heat is challenging. Medical records generally focus on the condition for which a patient is receiving treatment and do not necessarily indicate whether high temperatures contributed to its development.
Researchers at Northwestern University adopted a different approach, using a methodology inspired by genomic research.
They examined 1,803 diagnoses recorded during nearly one million visits to emergency departments and urgent-care facilities in Chicago between 2011 and 2023. During that period, there were 100 days of extreme heat, defined in the study as temperatures of at least 33.7°C.
The analysis identified 33 diagnoses associated with exposure to extreme heat. Some were already well known, while others had received comparatively little attention.
The conditions included skin rashes and swelling, acute kidney failure, multiple sclerosis, mental and behavioral disorders, insect bites, traffic accidents, as well as aggressive behavior and firearm-related injuries.
Daniel Horton, an associate professor of Earth, Environmental and Planetary Sciences at Northwestern and one of the study’s authors, noted that extreme heat can place stress on both the body and the brain. Increased irritability or reduced concentration, for example, could potentially contribute to behavioral changes and a higher risk of accidents.
The researchers argue that climate adaptation strategies may therefore need to address a much broader range of health effects than those traditionally associated with heatwaves.
Hundreds of millions of children face heat stress
The second study focused on the impact of climate change on children and produced particularly concerning findings.
As many as 560 million children aged nine and under, or approximately 43% of children in this age group worldwide, currently experience at least one month of heat stress every year as a result of human-caused climate change.
The researchers focused specifically on humid heat, the combination of high temperatures and high humidity. This condition can be especially dangerous because high humidity interferes with the evaporation of sweat, reducing the body’s ability to release heat and cool itself.
Children are particularly vulnerable to extreme heat. Their bodies heat up more quickly than those of adults, their sweating mechanisms are less efficient and they depend heavily on adults for protection. Excessive heat can cause dehydration and potentially life-threatening heatstroke, while prolonged exposure may also affect learning and cognitive development.
The impact of climate change is already evident. The number of children exposed to at least five months of heat stress each year has nearly tripled. Without the influence of climate change, researchers estimate that this figure would be around 120 million. Today, it stands at approximately 350 million.
The international research team, led by Vrije Universiteit Brussel, also found that children are exposed to extreme heat more than any other age group. Their exposure is nearly three times higher than that of people aged 60 to 69 facing a comparable additional heat-related health threat.
What happens if global temperatures continue to rise?
Climate projections indicate that the situation could become significantly worse.
Under a scenario in which global temperatures rise by 1.5°C, the number of children aged nine and under exposed to at least one month of dangerous heat is projected to reach 620 million, or around 49% of all children in this age group.
If warming reaches 2°C, the figure could rise to 650 million children, representing approximately 59%.
The Mediterranean is also expected to face a growing burden. Today, around 13.2 million children, or 19% of the region’s child population, experience at least one month of heat stress each year.
That number is projected to increase to 15.8 million under the 1.5°C warming scenario and to 21.1 million if global warming reaches 2°C.
The largest increases in exposure to dangerous humid heat are expected in tropical regions and poorer countries, where populations tend to be younger. South and Southeast Asia, along with West Africa, are already among the regions with the largest numbers of children exposed to dangerous levels of heat stress.
The findings underline a broader concern: as global temperatures continue to rise, the health consequences of extreme heat are likely to extend well beyond heatstroke and dehydration, affecting multiple aspects of human health with children facing a disproportionate share of the risk.