In a recent study published in Nature Medicine, researchers projected the number of heatstroke deaths by age and sex across Europe up to 2023. They also calculated the number of deaths that have been mitigated by societal adaptation to rising temperatures since 2000.
Study: Heatstroke mortality in Europe in 2023 and the role of adaptation to protect health. Image credit: aleks333/Shutterstock.com
background
Climate change is causing significant health impacts around the world, with Europe set to experience its hottest ever recorded temperature in global history and its second hottest ever recorded temperature in Europe in 2023. The world is likely to cross the 1.5°C threshold set out in the Paris Agreement by 2027, and summer heat-related health impacts pose challenges for European societies and public health systems.
In 2003, some European countries were forced to implement heat strategies after failing to address the health risks posed by hot summers. In 2022, more than 60,000 people died from heatstroke due to record summer temperatures, raising doubts about whether adaptation can avert deaths without temporary changes in heat exposure.
About the Research
In this study, the researchers quantified the burden of heatstroke mortality in 2023, calculated for weeks warmer than the minimum fatal temperature, and fitted an epidemiological model to factual and counterfactual scenarios to assess the role of adaptation in mitigating the number of deaths in 2023 under conditions of increasing temperature.
Adaptation refers to changes over time in exposure-response relationships, such as minimum mortality temperature and relative risk. The researchers analyzed temperature and mortality statistics for 823 adjacent regions in 35 countries, representing a European population of 543 million, built an epidemiological model for the pre-pandemic period 2015 to 2019, and projected the number of heatstroke deaths by sex and age in 2023.
The researchers projected heatstroke deaths in 2023 based on temporal changes in cumulative exposure-response relationships since 2000 that are attributable to socioeconomic improvements and climate change adaptation efforts. They fitted epidemiological models using data from several European countries spanning the periods 2000-2004, 2005-2009, 2010-2014 and 2015-2019.
The model allowed them to predict the number of deaths and mortality rates from heat stroke if the temperatures in 2023 occurred during the past historical period. The researchers fitted progressively older data to the model to estimate the increase in the number of deaths and mortality rates from heat stroke across all genders and age groups.
The researchers analyzed Eurostat's weekly all-cause mortality statistics by sex and age. The dataset includes 96,342,990 deaths (47,046,865 women and 46,780,242 men) from January 2000 to November 2023. The researchers used high-resolution ERA5-Land reanalysis data to convert hourly gridded 2-meter temperature data to weekly regional averages.
The researchers used quasi-Poisson regression models to determine the association between location-specific temperature lags and mortality in each European region. They aggregated location-specific coefficients using multivariate, multilevel meta-regression analysis. The researchers converted 2023 temperature and time-of-death data to heatstroke mortality rates with sensitivity analyses that considered seasonal and long-term trends.
result
The researchers project that there will be 47,690 heatstroke deaths in 2023 (47,312 from May 29 to October 1), the second-highest number of deaths from 2015 to 2023, behind only 2022. The researchers argue that if temperatures had risen between 2000 and 2004, without any adjustments this century, the number of heatstroke deaths across the population would have increased by 80%.
The increase was similar for women (83%) and men (86%) but differed significantly for those aged up to 64 years (63%), 65 to 79 years (79%), and 80 years and older (101%). Changes were fairly consistent over time, with larger changes seen from 2005 to 2009 and 2010 to 2014.
In 2023, the European Union reported 47,312 deaths due to heatstroke, with the highest mortality rates (per million inhabitants) in Southern Europe: Greece (393), Bulgaria (229), Italy (209), Spain (175), Cyprus (167), and Portugal (136). Women and the elderly had the highest mortality rates in Europe, with a female-to-male ratio of 1.6 for those aged 80 years and older and a ratio of 8.7 for those aged 65-79 years. Sensitivity analyses revealed limited sensitivity to parameter choices.
In 2023, two incidents in mid-July and late August accounted for 58% of all heatstroke deaths, with a notable increase in mortality in southern European countries and Germany from week 28 to week 29. Heatstroke deaths in weeks 33 and 34 were estimated at 14,407, affecting high-latitude regions such as the Baltic States.
The difference between the factual and counterfactual models arises from epidemiological correlations, in particular changes in minimum mortality temperatures over time: between 2000 and 2004 and between 2015 and 2019, the population as a whole warmed by 2.7°C, suggesting adaptation to relatively hotter conditions.
Conclusion
According to the study, the number of heatstroke deaths in 2023 was the second highest between 2015 and 2022, with 2022 being the highest.
Modern adaptations have helped reduce mortality, especially among older people. However, a more comprehensive open access dataset is needed for 23 countries. If the same percentage change occurred in 35 countries, the counterfactual number of deaths in 2023 would be 85,842, breaking the 2003 record.
The findings highlight the need for improved monitoring of the impacts of climate change on vulnerable individuals and proactive prevention programs for early adaptation.
