Highlights
- Over 3 million additional cases of stunting projected in south Asian children by 2050 due to climate change.
- Hot-humid conditions four times more harmful than heat alone during pregnancy's third trimester.
- Early and late pregnancy stages identified as most vulnerable periods for foetal development.
Climate change-driven heat and humidity could lead to more than three million additional cases of stunting among south Asia's children by 2050, according to a new study that highlights the severe health risks facing the world's most densely populated region.
Researchers at the University of California Santa Barbara examined how exposure to extremely hot and humid conditions during pregnancy impacts children's health, focusing on height-for-age measurements, a key indicator of chronic health status in children under five.
The findings, published in the journal Science, reveal that humidity significantly worsens the effects of heat exposure, partly because it prevents pregnant women from cooling down effectively.
Pregnant women are particularly susceptible to heat stress due to additional weight and hormonal changes that make them vulnerable to overheating.
"At the beginning of pregnancy, the foetus is very vulnerable, while at the end of pregnancy, the mother is more vulnerable," explained lead author Katie McMahon, a doctoral student at the university.
The research identified early and late pregnancy as the most critical periods, with the third trimester showing particularly alarming results.
Professor Kathy Baylis from the university's geography department noted that health outcomes from heat and humidity exposure during this period were approximately four times worse than those from heat alone.
Stunting future impact
The study utilised wet-bulb globe temperature measurements, which account for humidity, radiant heat and airflow beyond standard air temperature readings.
Researchers discovered that each additional day with maximum wet-bulb globe temperature exceeding 29 degrees Celsius was associated with reduced live births six to 12 months later.
Conversely, each extra day above 35 degrees Celsius correlated with increased birth rates within three months of exposure, suggesting hotter temperatures may be shifting births earlier while hot-humid conditions could be reducing conception rates or increasing early-stage pregnancy loss.
"Exposure to hot, humid conditions in-utero is dangerous for child health, and more dangerous than just hot temperatures alone," McMahon warned.
South Asia is projected to be among the world's worst affected regions as hot and humid conditions intensify under continued global warming.
The researchers cautioned that by focusing solely on temperature effects, health professionals may be underestimating the true impact of extreme weather on maternal and child health.
The study drew child health data from Demographic and Health Surveys, with weather data provided by the Climate Hazards Centre at the University of California Santa Barbara.
