Under-five mortality burden in low- and middle-income countries set to increase under future warming

The under-5 child mortality rate remains disproportionately high in low- and middle-income countries (LMICs). Children are particularly vulnerable to high temperatures, and climate change is expected to increase child mortality, yet few studies have investigated the relationship between ambient temperature and child mortality in LMICs. Here, using a sibling-matched case-control design, we examined the association between monthly ambient temperature and under-5 child mortality across 59 LMICs. We found that child mortality increased by 5.2%–10.3% under moderate to extreme temperature (32.0°C –34.9°C), compared to the reference temperature (25.0°C). Our estimates indicate high temperatures contributed to an estimated 5.7 deaths per 1,000 children in LMICs during 2000–2020. This number would increase by nearly 1.5, 2.9, and 3.2 times under the strict-, medium-, and high-emissions scenarios in 2090s, respectively. This study offers insight into the child mortality burden attributable to climate warming across historical and future periods in LMICs, emphasizing the vulnerabilities and inequalities of children in developing nations amid climate warming.