Climate change may raise risk of child stunting in South Asia by 2050: study

Climate change-driven hot and humid conditions could increase the number of stunted children in South Asia by more than three million by 2050, according to a new study by researchers at the University of California, Santa Barbara (UCSB).

The researchers examined how exposure to extreme heat and humidity during pregnancy affects child health outcomes in one of the world’s most densely populated regions. They analysed “height-for-age,” a widely used indicator of chronic undernutrition and poor health among children under five.

Pregnant women are particularly vulnerable to heat stress due to physiological and hormonal changes that make it harder for the body to regulate temperature.

The study, published in Science, found that humidity significantly worsens the effects of heat because it reduces the body’s ability to cool itself through sweating.

The most critical periods were identified as the very early and very late stages of pregnancy. “At the beginning of pregnancy, the fetus is very vulnerable, while at the end of pregnancy, the mother is more vulnerable,” said lead author Katie McMahon, a doctoral researcher at UCSB.

Exposure during the third trimester was especially harmful. Health impacts linked to combined heat and humidity were about four times more severe than those caused by heat alone, said Kathy Baylis, professor of geography at UCSB.

The study used wet-bulb globe temperature, which accounts for humidity, radiant heat, and airflow in addition to air temperature. Each additional day with a wet-bulb globe temperature above 29°C was associated with fewer live births six to twelve months later. Meanwhile, days exceeding 35°C were linked to a short-term rise in births, suggesting heat-related shifts toward earlier deliveries.

The findings align with earlier research showing that extreme heat increases premature births and pregnancy loss. With hot and humid conditions expected to intensify due to global warming, South Asia is likely to face some of the most severe health impacts.

By focusing only on temperature, the researchers warn, public health officials may be underestimating the true risks of climate change to maternal and child health. The study drew on child health data from Demographic and Health Surveys and climate data from UCSB’s Climate Hazards Center.