Approximately 583 million children under the age of ten worldwide are currently exposed to at least 20 additional days of heat stress annually as a result of human-caused warming, according to a new study published in Science Advances. This number represents 44% of all children in this age group, making them the population group most exposed to additional days of humid heat compared with other age groups.
The study combines climate models with demographic data and compares the current climate with the preindustrial climate to isolate the number of heat-stress days attributable to climate change. The researchers used the climate of 2023, which experienced global warming of 1.3 degrees Celsius due to human activity, as the baseline for the present.
Humid Heat Is the Risk Measure
The study does not measure temperature alone; it uses the indoor wet-bulb globe temperature, a measure that takes humidity into account. The researchers defined a heat-stress day as a day on which this temperature exceeds 28 degrees Celsius, the threshold used for moderate heat stress.
Heat becomes more dangerous as humidity rises because the evaporation of sweat becomes less effective at cooling the body. The results show that countries in tropical regions record the greatest number of additional days attributable to climate change. In Côte d’Ivoire, residents currently face 112 days of heat stress annually, with approximately half linked to human-caused warming, while Germany records an average of just 0.1 day annually according to this measure.
Why Is the Burden Concentrated on Children?
Children’s greater exposure is linked to two demographic and geographic factors. The world has approximately 1.3 billion children under the age of ten, compared with 600 million people aged 60–69. Regions in Africa and Asia—particularly South Asia, Southeast Asia, and West Africa—also combine high population-growth rates with a larger proportion of children.
By comparison, 190 million people aged 60–69 face at least 20 additional days of heat stress annually, representing 30% of this age group. However, the researchers and experts who reviewed the findings caution that the comparison may understate the relative burden on older adults, as some may live alone or face difficulty moving and accessing cooling or emergency assistance.
What Changes as Warming Increases?
Under the current climate, 11% of children under the age of ten face at least 100 additional days of heat stress annually. The proportion rises to 13% in a world that is 1.5 degrees Celsius warmer and to 23% when warming reaches 2 degrees Celsius, according to population projections based on the SSP2 scenario.
These figures show that increased warming not only raises the number of dangerous days but also expands the share of children affected by them. The finding is significant in discussions of climate justice because children in developing countries, which bear a large share of the exposure, have contributed less to historical emissions.
Limitations of the Finding and Open Questions
The number of heat-stress days alone does not mean that every child will experience the same health outcome. The study does not use an indicator designed specifically for children, and the resolution of the data did not capture the urban heat-island effect, which may lead to underestimation of local figures, particularly in cities. The researchers point to the need to connect climate, health, and education sciences to identify the measures most representative of the health and educational harms that children may face.
Adaptation also varies between communities; areas accustomed to heat may be more acclimatized, while communities in the mid-latitudes may face greater risks because of limited adaptation and urban infrastructure that is less suitable for dissipating heat. Therefore, the study provides a global estimate of exposure attributable to climate change, not a single prediction of the fate of every child or city.