Marine Heatwaves Linked to Higher Child Malnutrition Risk in Coastal Communities, PNAS Study Finds

Ocean warming reaches children's health on land

Marine heatwaves — periods of abnormally warm ocean temperatures lasting at least five days and sometimes extending for weeks or months — may have negative health effects on children in coastal communities in low- and middle-income countries, according to a study led by researchers at Penn State and the University of North Carolina at Chapel Hill.

The work, published in the Proceedings of the National Academy of Sciences in August 2026 and reported by Phys.org on 1 September, linked nationally representative data on children's and women's health from more than 9,800 coastal sites in 36 countries to global sea surface temperature records.

Lead author Clark Gray, a human geographer at UNC Chapel Hill, told reporters he had been "very ready to find nothing." Instead, the analysis found consistent associations between heatwave exposure and multiple dimensions of undernutrition and mortality.

Quantifying the health burden

The team estimated fixed-effects logistic regression models testing for heatwave effects on child mortality, child wasting, child stunting and adult underweight. They found that a one standard deviation increase in the number of heatwaves over a 24-month period — roughly three more heatwaves than normal — increased the odds of child mortality by 5.4%, child wasting by 6.5% and child stunting by 8.8%.

Effects extended to other dimensions of heatwaves, including maximum sea surface temperature and cumulative intensity. The associations were documented across 36 low- or middle-income countries where many households depend on local marine fisheries for protein, micronutrients and income.

Researchers said the findings suggest a need to target populations affected by marine heatwaves with nutrition-improving interventions or other safety-net programmes, particularly where fisheries disruptions reduce access to affordable protein.

Urban coastal communities among the hardest hit

One of the study's more surprising results is that urban populations showed the strongest associations. That pattern may reflect their position as purchasers rather than producers of protein-rich foods: when heatwaves disrupt fisheries and push fish prices higher, urban households with limited buffers can lose access to key nutrients quickly.

Marine heatwaves can deprive children of an important source of protein and micronutrients in utero and during their first five years of life, co-author Sally Dowd, an interdisciplinary fisheries scientist, told Inside Climate News. Reduced catch volumes and altered species composition stress both subsistence and market-dependent diets.

The study demonstrates correlation rather than a fully traced causal chain, and authors note that pathways linking ocean heat to land-based health outcomes are still being studied. Even so, the consistency of the signal across multiple health indicators has drawn attention from nutrition and climate policy communities.

A monitoring gap at a critical moment

Oceans absorb the majority of the planet's excess energy, and marine heatwaves are becoming more frequent and intense as human-caused climate change warms the world's oceans. Gray noted that in the broader context of global warming, heatwaves "are going to get worse."

The PNAS paper emphasises the continued importance of global monitoring for both child and maternal health and oceanic conditions. Without integrated surveillance, policymakers may miss a climate hazard that operates offshore but registers in clinic data onshore.