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?

  • 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.

  • 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?

  • 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.

  • 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.