Marine heatwaves and undernutrition in low- and middle-income countries.

Marine heatwaves are accelerating under climate change and increasingly threaten the lives and livelihoods of coastal populations, particularly in low- and middle-income countries where many households directly depend on local marine fisheries for protein, micronutrients, and income. To quantify this threat, we link individual-level data on child and maternal health from 9,813 coastal sites in 36 low- or middle-income countries to heatwave exposures in the nearby ocean, and use this linked dataset to estimate fixed-effects logistic regression models that test for heatwave effects on child mortality, wasting, and stunting, as well as adult underweight. We find that a 1 SD increase in the number of heatwaves over a 24-mo period increases the odds of child mortality by 5.4%, child wasting by 6.5% and child stunting by 8.8%, and that these effects also extend to other dimensions of heatwaves such as maximum sea surface temperature and cumulative intensity. Urban locations and countries more dependent on small-scale fishing are most strongly affected, and the majority of these results remain significant when we account for correlated atmospheric heatwaves. Taken together, these results document that marine heatwaves undermine human health and emphasize the need for additional research on the mechanisms connecting oceanic conditions to human health.