# Global Warming, Fertility, and Spermatogenesis Decline: Global and Regional Evidence from 195 Countries and Implications for Climate Adaptation Policy

## TL;DR

Global warming is linked to declining fertility in many countries, especially in regions with limited resources, highlighting the need for climate adaptation policies to protect reproductive health.

## Contribution

The study reveals that the impact of rising temperatures on fertility depends on a region's adaptive capacity, particularly in low-income areas.

## Key findings

- Global temperature anomalies are strongly correlated with declining fertility rates (r≈−0.90, p<0.001).
- In Africa and the Middle East, temperature remains a significant predictor of fertility decline even after accounting for GDP.
- Higher-income regions show reduced temperature effects on fertility, suggesting socioeconomic factors dominate in these areas.

## Abstract

Public health relevance—How does this work relate to a public health issue?
Rising global temperatures represent an emerging environmental stressor with measurable associations with fertility decline across 195 countries from 1960 to 2023, with potential implications for reproductive and population health worldwide.The biological sensitivity of spermatogenesis to heat exposure—operating through oxidative stress, germ cell apoptosis, and disrupted chromatin integrity—provides a plausible mechanistic pathway linking climate change to declining male reproductive health at the population level.

Rising global temperatures represent an emerging environmental stressor with measurable associations with fertility decline across 195 countries from 1960 to 2023, with potential implications for reproductive and population health worldwide.

The biological sensitivity of spermatogenesis to heat exposure—operating through oxidative stress, germ cell apoptosis, and disrupted chromatin integrity—provides a plausible mechanistic pathway linking climate change to declining male reproductive health at the population level.

Public health significance—Why is this work of significance to public health?
This study demonstrates that the association between global warming and fertility decline is not uniform but is critically conditioned by adaptive capacity: temperature anomalies remain significant predictors of fertility decline in Africa and the Middle East even after controlling for GDP per capita, while the effect attenuates in higher-income regions such as Europe, East Asia, and the Arctic.These findings highlight that populations with limited access to cooling infrastructure, occupational heat protections, and robust healthcare systems may face a disproportionate reproductive burden from rising temperatures, contributing to widening global health inequities.

This study demonstrates that the association between global warming and fertility decline is not uniform but is critically conditioned by adaptive capacity: temperature anomalies remain significant predictors of fertility decline in Africa and the Middle East even after controlling for GDP per capita, while the effect attenuates in higher-income regions such as Europe, East Asia, and the Arctic.

These findings highlight that populations with limited access to cooling infrastructure, occupational heat protections, and robust healthcare systems may face a disproportionate reproductive burden from rising temperatures, contributing to widening global health inequities.

Public health implications—What are the key implications or messages for practitioners, policy makers and/or researchers in public health?
Policymakers in low- and middle-income countries (LMIC) should integrate heat resilience strategies—including cooling infrastructure, occupational protections, and reproductive healthcare access—into climate adaptation planning to reduce climate-related reproductive vulnerability.Researchers should prioritize individual-level longitudinal studies linking personal heat exposure to biological reproductive endpoints (e.g., semen quality, pregnancy outcomes) to move beyond ecological associations and establish causal pathways informing evidence-based public health interventions.

Policymakers in low- and middle-income countries (LMIC) should integrate heat resilience strategies—including cooling infrastructure, occupational protections, and reproductive healthcare access—into climate adaptation planning to reduce climate-related reproductive vulnerability.

Researchers should prioritize individual-level longitudinal studies linking personal heat exposure to biological reproductive endpoints (e.g., semen quality, pregnancy outcomes) to move beyond ecological associations and establish causal pathways informing evidence-based public health interventions.

This study investigates whether long-term global warming is associated with fertility decline across 195 countries from 1960 to 2023, and whether this relationship varies by economic development and adaptive capacity. We analyze Total Fertility Rate (TFR) data from the World Bank alongside temperature anomaly measures from NOAA and NASA using Pearson correlations and ordinary least squares (OLS) regression models. Regional analyses include Africa, Asia, Europe, the Middle East, and the Arctic, with GDP per capita serving as a proxy for economic development and adaptive capacity. Globally, temperature anomalies and fertility exhibit a strong negative correlation (r≈−0.90, p<0.001). However, substantial regional heterogeneity emerges after controlling for GDP. In Africa (r=−0.89) and the Middle East, temperature anomalies remain statistically significant predictors of fertility decline even after GDP adjustment (β=−0.99, p<0.001; β=−1.27, p<0.001, respectively). In contrast, temperature effects become statistically insignificant in South Asia, East Asia, Europe, and the Arctic once GDP is controlled, indicating that fertility decline in these regions is driven primarily by socioeconomic modernization rather than climatic stress. These findings suggest that global warming functions as a conditional demographic stressor whose impact depends critically on adaptive capacity. In regions with limited infrastructure, including constrained access to air conditioning, healthcare, and occupational heat protection, rising temperatures remain significant predictors of fertility decline, potentially mediated through heat-sensitive biological mechanisms such as impaired spermatogenesis. By contrast, in higher-income regions, high adaptive capacity appears to buffer reproductive systems from thermal stress, allowing socioeconomic factors to dominate fertility dynamics.