In a recent study published in Nature Medicine, researchers projected age- and sex-specific heat-related deaths across Europe by 2023. They also calculated the death load saved via social adaptation to increasing temperatures since 2000.
Study: Heat-related mortality in Europe during 2023 and the role of adaptation in protecting health. Image Credit: aleks333/Shutterstock.com
Background
Climate change poses significant health hazards worldwide, with Europe experiencing the hottest record globally and the second-warmest in Europe in 2023. The world may cross the 1.5°C threshold set by the Paris Agreement by 2027, and summer heat-related health consequences pose challenges for European society and public health systems.
In 2003, some European nations failed to deal with the health repercussions of warm summers, prompting heat protection initiatives. In 2022, over 60,000 heat-related deaths were linked to record-breaking summer temperatures, casting doubt on the significance of adaptation in averting mortality without temporal changes in heat exposure.
About the study
In the present study, researchers quantified the heat-related death burden in 2023, computed for weeks warmer than the minimum mortality temperature, and fitted epidemiological models in factual-counterfactual scenarios to assess the role of adaptation in mitigating the 2023 death toll in the context of rising temperatures.
Adaptation denoted a time shift in exposure-response connections, such as the minimum mortality temperature and relative risks. Researchers analyzed temperature and death statistics from 823 contiguous areas across 35 nations, representing a population of 543 million Europeans, to construct epidemiological models for the pre-pandemic period 2015-2019, estimating sex- and age-specific heat-related deaths in 2023.
Researchers predicted heat-related fatalities in 2023 based on temporal changes in the cumulative exposure-response connection from 2000, ascribed to socioeconomic improvement and climate change adaptation efforts. They fitted epidemiological models using data from several European nations spanning 2000-2004, 2005-2009, 2010-2014, and 2015-2019.
The models enabled them to predict the number of deaths and rates connected with heat if temperatures for 2023 occurred in earlier historical periods. The researchers fitted models with data from increasingly older eras to estimate rising heat-related death numbers and rates in all sexes and age groups.
Researchers analyzed Eurostat's weekly all-cause death statistics by sex and age groups. The dataset included 96,342,990 death counts (47,046,865 for women and 46,780,242 for males) from January 2000 to November 2023. The researchers used high-resolution ERA5-Land reanalysis data to convert hourly gridded 2-m temperature data into weekly regional averages.
Researchers used quasi-Poisson regression models to determine location-specific temperature lag-mortality association in each European region. They aggregated location-specific coefficients using multivariate, multilevel meta-regression analysis. They converted temperature and death time data from 2023 to heat-related death rates, with sensitivity analysis considering seasonal and long-term trends.
Results
Researchers predicted 47,690 heat-related fatalities in 2023 (47,312 between 29 May and 1 October), the second largest mortality load from 2015-2023, only topped by 2022. They argue that if temperatures had occurred between 2000 and 2004, the overall population's heat-related death burden would have been 80% greater without current-century adjustments.
The increase was equivalent for women (83%) and males (86%), but it differed significantly for individuals aged up to 64 years (63%), 65 to 79 (79%), and above 80 (101%). Changes were reasonably consistent across time but showed higher shifts from 2005 to 2009 and 2010 to 2014.
In 2023, the European Union reported 47,312 heat-related fatalities, with Southern Europe having the highest mortality rates (per million), namely in Greece (393 deaths), Bulgaria (229 deaths), Italy (209 deaths), Spain (175 deaths), Cyprus (167 deaths), and Portugal (136 deaths). Women and the elderly have the highest death rates in Europe, with a women-to-men ratio of 1.6 and an elderly ratio of 8.7 for those over 80 and 65-79 years old, respectively. Sensitivity analysis revealed limited sensitivity to parameter selection.
In 2023, two incidents in mid-July and late August accounted for 58% of all heat-related deaths, with Southern European nations and Germany suffering significant mortality rates between weeks 28 and 29. Heat-related fatalities were estimated at 14,407 in weeks 33 and 34, impacting higher-latitude locations such as the Baltic nations.
Differences between factual and counterfactual models result from temporal changes in epidemiological correlations, particularly the minimum mortality temperature. Between 2000 and 2004, and 2015 and 2019, the overall population warmed by 2.7 degrees Celsius, suggesting adaptability to relatively hot conditions.
Conclusion
The study found that heat-related deaths in 2023 were the second highest between 2015 and 2022, with 2022 leading it.
Modern adaptation has helped to reduce mortality, particularly among elders. However, the 23 nations require more comprehensive open-access datasets. If the same percentage changes had occurred in 35 countries, the counterfactual mortality load would be 85,842 fatalities in 2023, breaking the 2003 record.
The findings underscore the need for improved monitoring of climate change's effects on vulnerable individuals and aggressive preventative programs for early adaptation.
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