Rising global temperatures due to increased carbon emissions pose a significant threat to public health, with frequent extreme heat events causing heat stroke, respiratory and cardiovascular diseases, and death. Historical heatwaves have resulted in tens of thousands of deaths globally. Substantial emission reduction is crucial to mitigate these negative impacts. The Intergovernmental Panel on Climate Change (IPCC) has provided new emission scenarios and climate projections using the Coupled Model Intercomparison Project phase 6 (CMIP6). China, with its large population, is experiencing significant warming and requires effective mitigation and adaptation strategies for climate change. While previous studies have assessed future health risks associated with heat in China, few have quantified the avoidable heat-related risks through emission reductions. This study aims to examine future avoidable heat-related mortality in China, considering population changes and the independent contributions of temperature and population changes to heat-related deaths. This will inform strategic planning and prioritization of healthcare infrastructure needs.

Existing research highlights the rising dangers of heat-related mortality due to climate change, particularly in densely populated areas. Studies have used CMIP6 datasets to project climate patterns, including those in China. Some studies have combined demographic projections and mortality records to assess future heat risks in China but have largely neglected to quantify the avoidable risks through emissions reduction, which is critical for effective infrastructure planning. The current warming trend in China exceeds the global average, with high latitudes and altitudes experiencing more significant warming. This underscores the necessity for robust healthcare infrastructure and prevention strategies.

This study used daily non-accidental mortality records from 195 sites across China, covering most climate zones. Eleven CMIP6 models were used, providing historical simulations (1900–2014) and future projections (2021–2100) under different emission scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5). A two-stage analysis was conducted to estimate the temperature-mortality relationship. The first stage used quasi-Poisson regression with a distributed lag non-linear model (DLNM) for each location. The second stage used multivariate meta-analysis to obtain a pooled temperature-mortality relationship for each region. Future heat-related mortality was projected by combining CMIP6 projected temperatures and the established exposure-response relationship. The independent contributions of temperature and population changes to heat-related deaths were quantified using Gini importance from Random Forest. Gross Domestic Product (GDP) and hospital bed data were used to explore the relationship between economic development and heat-related mortality.

Currently, natural climate change is the primary driver of heat-related deaths in China, with anthropogenic influences accounting for less than 50%. By 2100, under high-emission scenarios (SSP3-7.0 and SSP5-8.5), heat-related mortality could quadruple. Southern regions (East, South, and Southwest China) will experience the highest future mortality due to high heat-related mortality and large population size. Anthropogenic warming will increase over time and across emission scenarios. Temperature increases are the dominant contributor to heat-related deaths at high latitudes and altitudes, while population changes have a greater influence in Central and South China. Avoiding 48–72% of future heat-related mortality is possible through emission reduction. Over the next 20 years, anthropogenic warming could cause 15,576–87,612 additional deaths annually. Without historical human-induced emissions, China's lower economic and medical development would have increased current heat-related mortality by 57%.

The findings highlight the significant impact of both climate change and population dynamics on future heat-related mortality in China. Mitigation of greenhouse gas emissions is crucial, especially at high latitudes and altitudes. However, even under low-emission scenarios, heat-related deaths will remain significantly elevated in the near term. The substantial projected increase in heat-related deaths emphasizes the urgent need for improved healthcare infrastructure and emergency response strategies, especially in regions like Northwest and South China. The study also reveals a complex interplay between emission-induced economic development and heat-related mortality, suggesting that the benefits of economic advancement might offset some negative impacts of climate change. However, this requires further investigation.

This study demonstrates the significant potential for reducing future heat-related mortality in China through emission reduction, particularly at high latitudes and altitudes. However, immediate action on infrastructure and emergency response planning is crucial to manage near-term heat risks, as emission reduction effects won't be immediate. Future research should incorporate humidity and other meteorological factors into the exposure-response relationships, improve population projections, and develop comprehensive climate-health-economy models for more refined risk assessments.

Several limitations exist. The study primarily used temperature as a predictor for future heat-related mortality, omitting other factors like humidity. Population data did not include age details. Socioeconomic factors influencing adaptation to heat were not comprehensively considered. Uncertainties arise from temperature-mortality relationships and variations in CMIP6 model simulations. Although the study considered China's two-child policy, discrepancies from the actual population changes might still affect the results.