Climate change is causing a detectable rise in global temperatures, leading to more frequent and intense heat waves. The summer of 2022 witnessed record-breaking heat in Europe, posing a significant health threat to vulnerable populations. This study aimed to quantify the mortality burden associated with this extreme heat, focusing on the period between May 30th and September 4th, 2022. The research builds upon the societal awareness of heat's impact on health, which emerged after the devastating heat wave of 2003 that resulted in over 70,000 excess deaths across Europe. Since then, adaptation strategies have been implemented to protect at-risk populations, but the effectiveness of these strategies needs ongoing evaluation in light of the accelerating warming trends. This study aims to provide valuable insights into the mortality burden of the 2022 heat wave, comparing it with the 2003 event and considering the warming observed over the past decade. This information is crucial for informing the development and refinement of heat prevention plans and adaptation strategies to mitigate the growing threat posed by climate change.

Previous research has established a strong link between exposure to heat and increased morbidity and mortality, particularly during heat waves. The 2003 heat wave highlighted the vulnerability of European populations to extreme temperatures and the urgent need for effective heat prevention plans. Since then, research has focused on understanding the physiological and sociocultural factors contributing to heat-related mortality, including age, sex, socioeconomic status, and pre-existing health conditions. Studies have also explored the effectiveness of heat prevention plans in reducing heat-related health impacts, although evidence remains limited. Notably, past studies have observed decreasing trends in heat-related mortality in some European countries, suggesting that adaptation efforts have had some positive impact. However, the exceptional heat wave of 2022 underscores the need for continuous evaluation and strengthening of existing heat prevention plans and adaptation strategies to keep pace with the accelerating warming trends.

This multi-country study employed a two-stage statistical analysis to quantify the mortality burden specifically attributable to heat during the summer of 2022. The research utilized publicly available datasets: weekly counts of all-cause mortality according to sex and age groups from Eurostat, weekly regional averages of daily mean 2-meter temperature from the ERA5-Land reanalysis, and yearly regional population estimates from Eurostat. The analysis encompassed 823 contiguous regions representing over 543 million Europeans across 35 countries. The first stage involved using quasi-Poisson regression models to calculate the location-specific temperature-lag-mortality relationship for each European region. These models incorporated an intercept, a natural cubic spline of time to control for seasonal and long-term trends, and a cross-basis function to estimate the exposure-lag-response association between weekly temperatures and mortality counts. The second stage utilized a multivariate, multilevel meta-regression analysis to pool the location-specific coefficients obtained in the first stage. The meta-regression included country random effects, location-specific temperature average, temperature interquartile range, and the percentage of people aged 80 years and older as meta-predictors. This comprehensive approach allowed for the estimation of heat-related mortality numbers and rates at national and European levels, considering both spatial and temporal variations in temperature and mortality.

The study's key findings revealed a significant and alarming heat-related mortality burden during the summer of 2022, highlighting the urgent need for improved heat prevention and adaptation strategies. The study estimated 61,672 heat-related deaths across Europe between May 30th and September 4th, 2022. Italy, Spain, and Germany reported the highest numbers of heat-related deaths. The study also found notable sex and age-related disparities in heat-related mortality. Women experienced a 56% higher risk of heat-related death compared to men, with higher rates for men aged 0-64 and 65-79 years and for women aged 80 years and older. These findings underscore the importance of addressing the unique vulnerabilities of different population groups in heat prevention plans. Further analysis demonstrated a clear relationship between temperature and mortality risk, with a monotonically increasing risk of death for temperatures above and below the minimum mortality temperature. The study also identified a latitudinal pattern in heat-related mortality rates, with the highest rates observed in countries near the Mediterranean Sea, emphasizing the vulnerability of these populations to future heat waves. The analysis revealed that the summer of 2022 was the warmest season on record in Europe, exceeding the summer of 2003 in terms of average temperature. However, a comparison with the 2003 event necessitates cautious interpretation due to methodological differences. Despite the significant increase in heat-related mortality in 2022, the study found that the heat-related mortality burden was slightly lower than the excess mortality estimates reported for 2003. This suggests that some adaptation strategies have contributed to reducing heat-related mortality, but the effectiveness of these measures is still insufficient to fully mitigate the rising threat of extreme heat. The study also assessed the impact of warming trends over the past decade. The findings indicated a substantial increase in summer heat-related deaths compared to the period between 2015 and 2021, emphasizing the urgent need for enhanced adaptation strategies to address the accelerating warming trends. Projections suggest a rapid increase in summer heat-related mortality numbers in the coming years if no further adaptation measures are implemented.

The results of this study provide compelling evidence of the significant health consequences associated with record-breaking heat waves, especially in the context of accelerating climate change. The substantial heat-related mortality burden observed in the summer of 2022 highlights the urgent need for strengthening existing heat prevention plans and adaptation strategies across Europe. While previous efforts to mitigate heat-related mortality have shown some success, the magnitude of the 2022 event underscores the inadequacy of current measures. The study's findings on sex and age-related disparities in heat-related mortality emphasize the importance of tailoring prevention plans to address the unique vulnerabilities of different population groups. The latitudinal pattern of higher heat-related mortality rates near the Mediterranean Sea points to the heightened vulnerability of Southern European populations to future heat waves. These populations are expected to experience increasingly higher heat-related mortality in the coming years due to the ongoing warming trends. Addressing these geographical inequalities in vulnerability is crucial for mitigating the impact of climate change on human health. The study's findings raise important considerations regarding the effectiveness of heat prevention plans and the need for continuous evaluation and improvement. The magnitude of the 2022 heat-related mortality burden suggests that existing plans were only partially effective and highlights the need for a more comprehensive and effective approach to heat prevention and adaptation. Further research is needed to assess the biases associated with using weekly temperature and mortality data in epidemiological models, as this approach may underestimate the heat-related mortality burden. The study acknowledges the limitations related to data availability, particularly concerning the lack of cause-specific mortality data and the availability of data according to sex and age groups in all countries. Future research efforts should prioritize improving the accessibility and quality of data related to climate change and human health to better understand and address the complex factors contributing to heat-related mortality.

The findings of this study underscore the substantial and growing health consequences of climate change, particularly the impact of extreme heat events. The record-breaking temperatures experienced in Europe during the summer of 2022 led to a significant number of heat-related deaths, emphasizing the need for immediate and decisive action to mitigate the increasing threat. The study's findings call for a comprehensive reevaluation and strengthening of existing heat surveillance platforms, prevention plans, and long-term adaptation strategies to address the growing vulnerability of European populations to extreme heat. Governments and relevant agencies at national and European levels must prioritize the development and implementation of more effective heat prevention and adaptation plans, tailored to address the unique vulnerabilities of different population groups, particularly women and older adults. Addressing the geographic inequalities in vulnerability, especially in Southern Europe, is also critical to ensure equitable protection from the escalating impacts of climate change.

This study has several limitations that should be considered when interpreting the findings. Firstly, the use of weekly temperature and mortality data in the epidemiological models may have underestimated the heat-related mortality burden during the summer of 2022. Secondly, the study's analysis was limited by the availability of data according to sex and age groups in all countries. This underscores the need for coordinated efforts among national agencies to standardize and improve the collection and accessibility of health data, particularly concerning climate-related health impacts. Thirdly, the study utilized all-cause mortality data, which could have obscured the true impact of heat on specific causes of death. Further research using cause-specific mortality data is needed to gain a more comprehensive understanding of the health consequences of extreme heat.