Rising temperatures and humidity linked to reduced growth in children, study finds

Scientists are raising concerns about the lesser-known health impacts of climate change, warning that prolonged exposure to extreme heat—especially when combined with high humidity—during pregnancy could have lasting consequences for children’s development.

While the dangers of heatwaves are already well documented, researchers say the risks extend beyond immediate illness and mortality. The World Health Organization (WHO) has previously highlighted how extreme heat can worsen conditions such as cardiovascular disease, diabetes, and asthma. In Europe alone, approximately 24,400 deaths were linked to heatwaves during a recent summer, with scientists estimating that around two-thirds of those fatalities would not have occurred without human-driven climate change.

Now, a new study from University of California, Santa Barbara, published in Science Advances, suggests the long-term impacts of heat exposure—particularly when paired with humidity—may be more severe than previously understood. Researchers found that humid conditions intensify the body’s inability to cool itself, as sweating becomes less effective when moisture in the air slows evaporation.

Lead author Katie McMahon explained that this process can lead to heat stress even when temperatures are not at their highest. Pregnant women are especially vulnerable due to physiological changes, including increased body mass and hormonal shifts, which make it harder to regulate body temperature.

According to the study, heat stress during pregnancy can trigger premature labor and contribute to developmental complications that may affect children long after birth. Researchers emphasized that focusing only on heat-related deaths overlooks a broader range of health consequences linked to extreme weather.

To assess these impacts, scientists examined height-for-age ratios—a key indicator of long-term child health—in children under five. The findings revealed that those exposed to elevated heat and humidity throughout all stages of pregnancy were, on average, 13 percent shorter for their age than expected. By comparison, exposure to extreme heat alone was associated with a much smaller, roughly 1 percent reduction.

The research focused on populations in South Asia, a region considered particularly vulnerable to rising temperatures in the coming decades. Under a high-emissions scenario projected for 2050, the study estimates that approximately 3.5 million children in the region could experience stunted growth linked to prenatal exposure to extreme heat and humidity.

The findings underscore the growing body of evidence that climate change is not only an environmental issue but also a major public health challenge, with effects that may begin before birth and shape outcomes across a lifetime.