Study warns climate change could worsen child stunting in South Asia by 2050

Hot and humid conditions driven by climate change could result in more than three million additional cases of child stunting in South Asia by 2050, a new study has warned.

Researchers from the University of California, Santa Barbara examined how exposure to extreme heat and humidity during pregnancy affects child growth and health outcomes in the region. The study assessed “height-for-age”, a standard indicator of chronic malnutrition and long-term health in children under five.

Published in the journal Science, the research found that humidity significantly worsens the impact of heat exposure by limiting the body’s ability to cool down. Pregnant women are especially vulnerable to heat stress due to physiological changes during pregnancy, increasing risks to both mother and fetus.

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

Analysis showed that exposure during the third trimester to combined heat and humidity led to health impacts nearly four times greater than those caused by high temperatures alone, said Kathy Baylis, a professor of geography at UCSB.

To capture heat stress more accurately, the researchers used wet-bulb globe temperature (WBGT), which factors in humidity, radiant heat and airflow in addition to air temperature. The study also observed demographic effects. Each additional day with maximum WBGT above 29 degrees Celsius was linked to fewer live births six to 12 months later, while days with temperatures above 35 degrees Celsius were associated with a short-term rise in births within three months.

These trends are consistent with earlier findings that extreme heat can hasten childbirth, while sustained hot and humid conditions may reduce conception rates, increase early pregnancy loss, or both. “Hot-humid exposure in utero poses a serious threat to child health and is more harmful than heat alone,” McMahon said.

With global warming expected to intensify such conditions, South Asia — one of the world’s most densely populated regions — faces disproportionate risks. The researchers cautioned that focusing solely on temperature may lead policymakers and public health authorities to underestimate the full health impacts of extreme weather.

The study drew on child health data from the Demographic and Health Surveys and daily weather data from UCSB’s Climate Hazards Center.