Abstract
Objective
Climate change is expected to increase global temperatures. How temperature-related mortality risk will change is not completely understood, and how future demographic changes will affect temperature-related mortality needs to be clarified. We evaluate temperature-related mortality across Canada until 2099, accounting for age groups and scenarios of population growth.
Methods
We used daily counts of non-accidental mortality for 2000 to 2015 for all 111 health regions across Canada, incorporating in the study both urban and rural areas. A two-part time series analysis was used to estimate associations between mean daily temperatures and mortality. First, current and future daily mean temperature time series simulations were developed from Coupled Model Inter-Comparison Project 6 (CMIP6) climate model ensembles from past and projected climate change scenarios under Shared Socioeconomic Pathways (SSPs). Next, excess mortality due to heat and cold and the net difference were projected to 2099, also accounting for different regional and population aging scenarios.
Results
For 2000 to 2015, we identified 3,343,311 non-accidental deaths. On average, a net increase of 17.31% (95% eCI: 13.99, 20.62) in temperature-related excess mortality under a higher greenhouse gas emission scenario is expected for Canada in 2090–2099, which represents a greater burden than a scenario that assumed strong levels of greenhouse gas mitigation policies (net increase of 3.29%; 95% eCI: 1.41, 5.17). The highest net increase was observed among people aged 65 and over, and the largest increases in both net and heat- and cold-related mortality were observed in population scenarios that incorporated the highest rates of aging.
Conclusion
Canada may expect net increases in temperature-related mortality under a higher emissions climate change scenario, compared to one assuming sustainable development. Urgent action is needed to mitigate future climate change impacts.
Résumé
Objectif
Les changements climatiques devraient accroître les températures mondiales. La façon dont le risque de mortalité lié à la température évoluera n’est pas entièrement comprise, et la façon dont les changements démographiques futurs influeront sur la mortalité liée à la température doit être clarifiée. Nous étudions la mortalité liée à la température au Canada jusqu’en 2099, en tenant compte des groupes d’âge et des scénarios de croissance démographique.
Méthodes
Nous avons utilisé les nombres quotidiens de mortalité non accidentelle pour 2000 à 2015 pour toutes les 111 régions socio sanitaires du Canada, en intégrant dans l’étude des régions urbaines et rurales. Une analyse en séries chronologiques en deux parties a été utilisée pour estimer les associations entre les températures quotidiennes moyennes et la mortalité. Premièrement, des simulations de séries chronologiques de températures moyennes quotidiennes actuelles et futures ont été élaborées à partir d’ensembles de modèles climatiques du Projet de comparaison croisée 6 (CMIP6) du modèle couplé à partir de scénarios de changements climatiques passés et projetés dans le cadre de voies socioéconomiques partagées (SSP). Ensuite, la surmortalité due à la chaleur et au froid et la différence nette ont été projetées jusqu’en 2099, ce qui tient également compte de différents scénarios régionaux et de vieillissement de la population.
Résultats
De 2000 à 2015, nous avons recensé 3 343 311 décès non accidentels. En moyenne, une augmentation nette de 17,31% (eCI à 95%: 13,99, 20,62) de la mortalité excessive liée à la température dans le cadre d’un scénario d’émissions de gaz à effet de serre plus élevées est prévue pour le Canada en 2090–2099, ce qui représente un fardeau plus lourd qu’un scénario qui suppose des niveaux élevés de politiques d’atténuation des émissions de gaz (augmentation nette de 3,29%; eCI à 95%: 1,41, 5,17). La plus forte augmentation nette a été observée chez les personnes de 65 ans ou plus, et les plus fortes augmentations de la mortalité nette, de mortalité liée à la chaleur et au froid ont été observées dans les scénarios de population qui comprenaient les taux de vieillissement les plus élevés.
Conclusion
Le Canada pourrait s’attendre à des augmentations nettes de la mortalité liée à la température dans le cadre d’un scénario de changement climatique à émissions plus élevées, comparativement à un scénario de développement durable. Des mesures urgentes sont nécessaires pour atténuer les répercussions futures des changements climatiques.
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Introduction
Climate change represents a leading global health threat for the twenty-first century (Watts et al., 2018). In Canada, surface temperatures have risen by 1.7 °C since 1948 (Bush & Lemmen, 2019) and are expected to increase about a further 5.44 °C in major cities towards the end of the century under the higher greenhouse gas emission scenario (Lee et al., 2019).
Sub-optimal temperature exposures are associated with a range of conditions that impact health, directly and indirectly. Temperature stress can have an indirect relationship with a variety of mortality causes, beyond hypo- and hyperthermia, and may exacerbate underlying conditions and result in increased mortality (Ebi et al., 2021). Studies have projected health impacts associated with changes in ambient temperature for the next century, predicting an increase in heat-related mortality (Gasparrini et al., 2017; Guo et al., 2018; Martínez-Solanas et al., 2021; Wang et al., 2022; Weinberger et al., 2018). However, most studies have focused mainly on major cities or urban areas and therefore have yet to incorporate temperature-health projections for rural and northern latitudes. Therefore, mortality projections are often based on estimates from major cities, ignoring possible urban–rural differences which may result in incorrect estimations (Chen et al., 2016; Hu et al., 2019). In addition, debates remain as to whether an increase in heat-related health impacts would be offset by decreases in cold-related health consequences. Furthermore, changing demographics and population aging are likely to impact climate change and health burdens. The elderly are particularly at risk from non-optimal temperatures (Benmarhnia et al., 2015), and accounting for population changes, in particular by age subgroups at fine geographical spatial resolution, will improve understanding of future risks (Chen et al., 2020; Harper et al., 2021; ** strategies to contain global warming and prevent adverse health impacts.
Understanding the future trajectory of temperature-related mortality under climate change is improved by accounting for health region–specific population change, with the geographic specificity representing an advance over using previously available national-, provincial-, and territorial-level projections (Chen et al., 2020). The different population change scenarios used indicated a wide difference in projected mortality rates. The scenarios that incorporated the greatest degree of aging indicated the largest increases in both net and heat- and cold-related mortality. Impacts were also greater in those aged 65 and over, consistent with recent research (Chen et al., 2020).
In a qualitative analysis of local health authority needs for adapting to the impacts of climate change, Austin et al. (2019) identified the estimation or quantification of the disease burden of climate change on health as a priority. Here we provide quantitative information that can be used at the local health authority level for climate change adaptation planning, as well as at the national level to project climate change risks for Canada as a whole. These climate change and health risk estimates and projections are also a key step in the Building Resilience Against Climate Effects (BRACE) framework, developed to facilitate public health adaptation to climate change (Marinucci et al., 2014).
Limitations of the study
Some limitations must be acknowledged. We did not account for potential population adaption to future temperatures (Arbuthnott et al., 2016); our approach allowed us to explore the impacts of different climate change and population growth scenarios on projected mortality risk, but relies on the assumption that the relationship between temperature and mortality will be stable over time. As Canada is getting older, demographic trends could increase populations at higher risk for such impacts, while mitigation and adaptation could decrease these risks, and modify the temperature-mortality relationship over the long-time horizon that we used. In addition, we also did not account for potential changes in urbanization, as mentioned above (** public health policies at the health authority scale, and strategies for climate change mitigation and adaptation at both national and local levels. Future research should try to incorporate more information on adaptation measures implemented over time as well as more precise susceptibility variables of exposed groups in health regions, in order to adjust future simulations.
Contributions to knowledge
What does this study add to existing knowledge?
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Few studies in Canada have examined whether temperature-related impacts are expected to increase with climate change. In this population-scale study, we consider changing demographics, population aging, and different climate model scenarios, to project future climate-related health risks due to climate change.
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This study was conducted at the administrative health region geographic scale, so temperature-related mortality risk estimates will be of practical use to public health authorities in vulnerability and adaptation planning.
What are the key implications for public health interventions, practice, or policy?
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We find a net increase in temperature-related excess mortality is expected in Canada, that temperature-related mortality is highest under a higher emission scenario, that higher population growth will amplify temperature-related mortality, and that the highest net increase is expected among people over 65.
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These findings should be informative in continued efforts in develo** public health policies, and strategies for climate change mitigation and adaptation at both national and local levels.
Availability of data and material
All data used in our study were obtained under a data-sharing agreement between Health Canada and Statistics Canada, and cannot be made publicly available.
Code availability
R codes used for this study can be made available upon request.
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Funding
Open access funding provided by Health Canada. This study was funded by the Addressing Air Pollution Horizontal Initiative program of Heath Canada.
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All authors contributed to the study conception and design. Data collection was performed by MacDonald, Gosselin, Lavigne, and Hebbern. Data analysis was conducted by Lavigne and Hebbern. The first draft of the manuscript was written by Lavigne and Hebbern and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
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Hebbern, C., Gosselin, P., Chen, K. et al. Future temperature-related excess mortality under climate change and population aging scenarios in Canada. Can J Public Health 114, 726–736 (2023). https://doi.org/10.17269/s41997-023-00782-5
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DOI: https://doi.org/10.17269/s41997-023-00782-5