The loss of lifetime related to heat exposure attributable to human-induced climate change

Recent evidence shows that anthropogenic climate change is responsible for a large share of heat-related mortality and morbidity globally. Over long time scales, these impacts are modified by demographic and socioeconomic trends, such as population ageing and increasing life expectancy. To better evaluate the societal burden of climate change over time, attribution of impacts beyond mortality counts and risks is needed, including metrics that capture both the quality and length of life.

In this study, we quantify the loss of lifetime attributable to climate change resulting from deaths related to heat and cold. We combine life tables with individual-level mortality data from Mexico, Spain, and Switzerland. We apply state-of-the-art health-impact attribution methods to estimate the association between temperature and years of life lost based on the age at death of each individual. We stratify our analysis by sex and age groups, and aggregate our results to the state level. We obtain observed exposure temperature data from ERA5Land and derive yearly and country-specific counterfactual temperatures by linearly regressing local warming from reanalysis and simulated datasets on attributable global mean surface temperature change.

We show that climate change-attributable heat-related loss of lifetime has increased globally in recent decades. This burden is consistently shifting towards younger individuals. At least 50% is shouldered by individuals who lost more than 20 years of their expected lifetime (i.e., younger than approximately 67 years old in 2024) in Switzerland and Mexico,  while in Spain, this share reached 77% already. This increasing heat-related burden is leading to more frequent net losses of lifetime in younger individuals in recent years, accounting for both heat and cold-related deaths. Nevertheless, the attributable net effects of climate change on the entire population are generally negative, driven by a larger reduction in cold exposure in the older population. For older individuals, the net effect shows a decreasing trend with ongoing climate change, which leads to an extension of lifetimes. Only extreme years, like 2003 in Spain and Switzerland, show a net shortening of lifetime across the entire population.

These findings suggest increasing pressure from climate change on heat-vulnerable individuals, reducing their expected lifetime disproportionately. Importantly, this is not exclusive to individuals close to their life expectancy, as individuals with more than 20 years yet to live are the main contributors to attributable years of life lost. These younger individuals are already experiencing climate change as a pressure on their life expectancy across the whole temperature range. In the future, exposure to more frequent and extreme heat could lead to a net loss in lifetime in the overall population, therefore decreasing life expectancy. Our results provide a more nuanced view of which group carries the disproportional burden of climate change health impacts.