The escalating atmospheric concentrations of greenhouse gases (GHGs) due to human activities have resulted in significant climate change. The past decade has been the warmest on record, with global mean temperatures exceeding pre-industrial levels by 0.95-1.2 °C. Exposure to high ambient temperatures poses a considerable threat to human health, particularly for vulnerable populations with limited physiological and socioeconomic adaptive capacities. Neonates are especially susceptible due to their immature thermoregulatory systems, higher metabolic rates, lower sweating rates, smaller blood volume, higher heart rates, and high surface-area-to-mass ratios, making them prone to both hypothermia and hyperthermia. Severe infections further increase vulnerability. In 2019, approximately 2.4 million neonatal deaths occurred globally, with the majority (91%) in low- and middle-income countries (LMICs). Most existing research on temperature and neonatal mortality focuses on high-income settings, leaving a gap in understanding the impact in LMICs and the role of climate change. This study aims to fill this gap by quantifying the contribution of climate change to temperature-related neonatal deaths in 29 LMICs between 2001 and 2019.

The literature on ambient temperatures and neonatal mortality is limited, particularly for LMICs. While some studies show associations with high temperatures, others report links to low temperatures. Existing research lacks quantification of the impact of climate change. Most impact attribution studies have focused on natural systems, with limited attention to human health, especially in children and LMICs. This study builds on the Intersectoral Impact Model Intercomparison Project (ISIMIP) framework, combining DHS data with temperature reanalysis datasets to address this knowledge gap.

This study employed a two-stage analysis. The first stage involved a time-stratified case-crossover analysis using DHS data (n=40,073) from 29 LMICs (2001-2019). This design controls for time-invariant individual confounders. The analysis quantified the non-linear association between daily ambient temperatures and neonatal mortality, considering both overall neonatal deaths (0-28 days) and very early neonatal deaths (0 days). Absolute temperatures were standardized into location-specific temperature percentiles to account for population adaptation. Conditional logistic regression and distributed lag non-linear models were used with three bias-adjusted global observational temperature datasets from ISIMIP to estimate exposure-response associations. The second stage used the exposure-response functions to compute the burden of temperature-related neonatal deaths under factual (observed temperatures) and counterfactual (temperatures without the climate change signal) scenarios. The difference between these scenarios provided the excess number of neonatal deaths attributable to climate change. The analysis followed the IPCC Working Group II definition of impact attribution, focusing on impacts from climate changes irrespective of their causes. Sensitivity analyses were conducted using shorter recall periods and different knot placements in the models. Uncertainty estimates were derived using Monte Carlo simulations.

Across all study locations, 4.3% (95% UI: 1.7–6.8%) of neonatal deaths were associated with non-optimal temperatures. Heat-related deaths accounted for 1.5% (95% UI: 0.2–2.6%) and cold-related deaths for 2.9% (95% UI: 1.5–4.1%) of the total burden. Climate change contributed to 32% (country range: 19–79%) of heat-related neonatal deaths (175,133 additional deaths, 95% UI: 7806–353,516), representing a 46% increase compared to the counterfactual scenario. Conversely, climate change reduced cold-related deaths by 30% (country range: 10–63%), equivalent to 457,384 fewer deaths (95% UI: 170,106–868,519). The largest impacts of climate change (both increased heat-related and decreased cold-related mortality) were observed in countries with high baseline neonatal mortality rates and significant temperature increases. For very early neonatal deaths, climate change contributed to 29% (country range: 8–72%) of heat-related deaths (168,835 deaths, 95% UI: 48,835–296,467) and reduced cold-related deaths by 35% (country range: 10–69%), amounting to 141,322 fewer deaths (95% UI: 2377–339,337). Moderately hot and cold temperatures, rather than extremes, contributed most to the overall burden. Very early neonates appeared more vulnerable to heat than cold, possibly due to different causal pathways (e.g., prematurity and birth complications linked to in utero heat exposure).

This study's findings demonstrate that climate change is already impacting neonatal health in LMICs by altering ambient temperatures. The increase in heat-related mortality outweighs the reduction in cold-related mortality. The results are consistent with existing evidence on neonatal hypothermia and hyperthermia risks in LMICs. The mixed findings in previous studies regarding temperature associations with mortality may be due to the inclusion of both heat and cold in the current analysis, the use of temperature percentiles, and the focus on understudied populations. While this study's results are not directly comparable to others due to its inclusion of both heat and cold components and use of temperature percentiles, they align with previous findings on substantial heat-related mortality burdens in adults from climate change. The observed 46% increase in heat-related neonatal mortality is lower than a previous study's finding of a doubling of heat-related child mortality in Africa, potentially due to differences in age groups and methodology. The study highlights the need for public health interventions to protect newborns from both high and low temperatures, including improved thermal practices, home and healthcare facility improvements, and community education programs. These should be part of a broader effort to reduce overall neonatal mortality, given that temperature-related deaths constitute a smaller fraction of the overall burden.

This study provides the first evidence of climate change's contribution to temperature-related neonatal deaths in LMICs. The analysis, using a robust methodology and large dataset, demonstrates that climate change is already affecting child health, exacerbating heat-related and mitigating cold-related mortality. Continued warming is expected to worsen the heat-related burden. This underscores the urgent need for ambitious mitigation and adaptation strategies to protect vulnerable populations.

Limitations include reliance on self-reported DHS data, potential misreporting of neonatal deaths, and the use of temperature percentiles which might underestimate the impact of extreme heat events. The analysis did not account for changes in exposure-response functions over time or distinguish between impacts from anthropogenic greenhouse gases and other climate influences. Certain regions, such as Latin America, were underrepresented due to data availability. The disproportionate representation of India in the sample may also affect generalizability. Future research should leverage more comprehensive and geographically detailed data sources for more robust estimates.