Researchers warn that extremely hot, humid conditions during pregnancy could stunt children’s growth. Millions of children risk shorter stature if heat-trapping emissions continue to warm the planet.
Heat already threatens human health
The dangers of extreme heat are well documented. The World Health Organisation reports that high temperatures worsen illnesses such as cardiovascular disease, diabetes, and asthma. This summer, heatwaves killed around 24,400 people across Europe. Scientists calculate that 16,500 of these deaths could have been avoided without human-caused warming, meaning climate change tripled the death toll. Researchers at UC Santa Barbara now say the risks of extreme weather extend far beyond what doctors and scientists have realized.
How humidity amplifies the danger
A new study in Science Advances shows that humidity worsens the effects of heat. Humans cool down by sweating, but evaporation slows when the air holds more moisture. Lead author Katie McMahon explains that the trapped heat raises body temperatures, causing heat stress. This effect can occur even at moderate temperatures if humidity is high. Pregnant women face greater risks due to weight gain and hormonal changes that make overheating more likely. Heat stress can trigger premature labor, which leads to developmental problems and long-term health issues in children. McMahon emphasizes that extreme weather harms many more people than it kills, and focusing only on deaths underestimates its impact.
Can climate change stunt children’s growth?
Researchers measured children’s height relative to the average for their age, a key indicator of chronic health in those under five. They found that children exposed to heat and humidity in all three trimesters would be 13 percent shorter than expected. Exposure to extreme heat alone reduced height by only 1 percent. The study focused on pregnant women in South Asia, a region particularly vulnerable to rising temperatures. Under high-emission scenarios projected for 2050, around 3.5 million children in the region could experience stunted growth. Even if warming is limited to 2°C above preindustrial levels, deadly heat events will strike South Asia every year, the authors warn.
