Associations Between Extreme Temperatures and Cardiovascular Cause-Specific Mortality: Results From 27 Countries.

BACKGROUND: Cardiovascular disease is the leading cause of death worldwide. Existing studies on the association between temperatures and cardiovascular deaths have been limited in geographic zones and have generally considered associations with total cardiovascular deaths rather than cause-specific cardiovascular deaths. METHODS: We used unified data collection protocols within the Multi-Country Multi-City Collaborative Network to assemble a database of daily counts of specific cardiovascular causes of death from 567 cities in 27 countries across 5 continents in overlapping periods ranging from 1979 to 2019. City-specific daily ambient temperatures were obtained from weather stations and climate reanalysis models. To investigate cardiovascular mortality associations with extreme hot and cold temperatures, we fit case-crossover models in each city and then used a mixed-effects meta-analytic framework to pool individual city estimates. Extreme temperature percentiles were compared with the minimum mortality temperature in each location. Excess deaths were calculated for a range of extreme temperature days. RESULTS: The analyses included deaths from any cardiovascular cause (32 154 935), ischemic heart disease (11 745 880), stroke (9 351 312), heart failure (3 673 723), and arrhythmia (670 859). At extreme temperature percentiles, heat (99th percentile) and cold (1st percentile) were associated with higher risk of dying from any cardiovascular cause, ischemic heart disease, stroke, and heart failure as compared to the minimum mortality temperature, which is the temperature associated with least mortality. Across a range of extreme temperatures, hot days (above 97.5th percentile) and cold days (below 2.5th percentile) accounted for 2.2 (95% empirical CI [eCI], 2.1-2.3) and 9.1 (95% eCI, 8.9-9.2) excess deaths for every 1000 cardiovascular deaths, respectively. Heart failure was associated with the highest excess deaths proportion from extreme hot and cold days with 2.6 (95% eCI, 2.4-2.8) and 12.8 (95% eCI, 12.2-13.1) for every 1000 heart failure deaths, respectively. CONCLUSIONS: Across a large, multinational sample, exposure to extreme hot and cold temperatures was associated with a greater risk of mortality from multiple common cardiovascular conditions. The intersections between extreme temperatures and cardiovascular health need to be thoroughly characterized in the present day-and especially under a changing climate.

Extreme Temperatures and Stroke Mortality: Evidence From a Multi-Country Analysis.

BACKGROUND: Extreme temperatures contribute significantly to global mortality. While previous studies on temperature and stroke-specific outcomes presented conflicting results, these studies were predominantly limited to single-city or single-country analyses. Their findings are difficult to synthesize due to variations in methodologies and exposure definitions. METHODS: Within the Multi-Country Multi-City Network, we built a new mortality database for ischemic and hemorrhagic stroke. Applying a unified analysis protocol, we conducted a multinational case-crossover study on the relationship between extreme temperatures and stroke. In the first stage, we fitted a conditional quasi-Poisson regression for daily mortality counts with distributed lag nonlinear models for temperature exposure separately for each city. In the second stage, the cumulative risk from each city was pooled using mixed-effect meta-analyses, accounting for clustering of cities with similar features. We compared temperature-stroke associations across country-level gross domestic product per capita. We computed excess deaths in each city that are attributable to the 2.5% hottest and coldest of days based on each city's temperature distribution. RESULTS: We collected data for a total of 3 443 969 ischemic strokes and 2 454 267 hemorrhagic stroke deaths from 522 cities in 25 countries. For every 1000 ischemic stroke deaths, we found that extreme cold and hot days contributed 9.1 (95% empirical CI, 8.6-9.4) and 2.2 (95% empirical CI, 1.9-2.4) excess deaths, respectively. For every 1000 hemorrhagic stroke deaths, extreme cold and hot days contributed 11.2 (95% empirical CI, 10.9-11.4) and 0.7 (95% empirical CI, 0.5-0.8) excess deaths, respectively. We found that countries with low gross domestic product per capita were at higher risk of heat-related hemorrhagic stroke mortality than countries with high gross domestic product per capita (P=0.02). CONCLUSIONS: Both extreme cold and hot temperatures are associated with an increased risk of dying from ischemic and hemorrhagic strokes. As climate change continues to exacerbate these extreme temperatures, interventional strategies are needed to mitigate impacts on stroke mortality, particularly in low-income countries.

Global, regional, and national burden of heatwave-related mortality from 1990 to 2019: A three-stage modelling study.

BACKGROUND: The regional disparity of heatwave-related mortality over a long period has not been sufficiently assessed across the globe, impeding the localisation of adaptation planning and risk management towards climate change. We quantified the global mortality burden associated with heatwaves at a spatial resolution of 0.5°×0.5° and the temporal change from 1990 to 2019. METHODS AND FINDINGS: We collected data on daily deaths and temperature from 750 locations of 43 countries or regions, and 5 meta-predictors in 0.5°×0.5° resolution across the world. Heatwaves were defined as location-specific daily mean temperature ≥95th percentiles of year-round temperature range with duration ≥2 days. We first estimated the location-specific heatwave-mortality association. Secondly, a multivariate meta-regression was fitted between location-specific associations and 5 meta-predictors, which was in the third stage used with grid cell-specific meta-predictors to predict grid cell-specific association. Heatwave-related excess deaths were calculated for each grid and aggregated. During 1990 to 2019, 0.94% (95% CI: 0.68-1.19) of deaths [i.e., 153,078 cases (95% eCI: 109,950-194,227)] per warm season were estimated to be from heatwaves, accounting for 236 (95% eCI: 170-300) deaths per 10 million residents. The ratio between heatwave-related excess deaths and all premature deaths per warm season remained relatively unchanged over the 30 years, while the number of heatwave-related excess deaths per 10 million residents per warm season declined by 7.2% per decade in comparison to the 30-year average. Locations with the highest heatwave-related death ratio and rate were in Southern and Eastern Europe or areas had polar and alpine climates, and/or their residents had high incomes. The temporal change of heatwave-related mortality burden showed geographic disparities, such that locations with tropical climate or low incomes were observed with the greatest decline. The main limitation of this study was the lack of data from certain regions, e.g., Arabian Peninsula and South Asia. CONCLUSIONS: Heatwaves were associated with substantial mortality burden that varied spatiotemporally over the globe in the past 30 years. The findings indicate the potential benefit of governmental actions to enhance health sector adaptation and resilience, accounting for inequalities across communities.

Spatio-temporal evolution of heat waves severity and expansion across the Iberian Peninsula and Balearic islands.

In the current climate change scenario, heat waves have become one of the most concerning extreme climatic events, both because of their implications for human health and the economy, and because of their increase in intensity and frequency in recent decades. This work presents for the first time a climatological analysis of heat waves in the Iberian Peninsula and Balearic Archipelago (IPB) using the Excess Heat Factor index (EHF). This index considers the factor of intensity and the acclimatization process of human body in the study of heat waves. We focused on the intensity (also called severity), duration, frequency and spatial extension of heat waves in the IPB in the 1950-2020 period. The exceptional heat wave of August 2018 was approached in a similar way to further explore the usefulness of the EHF index. We found that the EHF index identified heat wave conditions 2 days earlier than indices that used only maximum temperatures. Results showed a significant increase in intensity, duration, frequency and spatial extension of heat waves for the whole IPB for 1950-2020 period. The average extent of heat waves increased by 4.0% per decade and the maximum extent by 4.1% per decade. This trend suggested a significant increase in human exposure, droughts, fire risk and energy demand in this region in the last decades.

Effects of Hot Nights on Mortality in Southern Europe.

BACKGROUND: There is strong evidence concerning the impact of heat stress on mortality, particularly from high temperatures. However, few studies to our knowledge emphasize the importance of hot nights, which may prevent necessary nocturnal rest. OBJECTIVES: In this study, we use hot-night duration and excess to predict daily cause-specific mortality in summer, using multiple cities across Southern Europe. METHODS: We fitted time series regression models to summer cause-specific mortality, including natural, respiratory, and cardiovascular causes, in 11 cities across four countries. We included a distributed lag nonlinear model with lags up to 7 days for hot night duration and excess adjusted by daily mean temperature. We summarized city-specific associations as overall-cumulative exposure-response curves at the country level using meta-analysis. RESULTS: We found positive but generally nonlinear associations between relative risk (RR) of cause-specific mortality and duration and excess of hot nights. RR of duration associated with nonaccidental mortality in Portugal was 1.29 (95% confidence interval [CI] = 1.07, 1.54); other associations were imprecise, but we also found positive city-specific estimates for Rome and Madrid. Risk of hot-night excess ranged from 1.12 (95% CI = 1.05, 1.20) for France to 1.37 (95% CI = 1.26, 1.48) for Portugal. Risk estimates for excess were consistently higher than for duration. CONCLUSIONS: This study provides new evidence that, over a wider range of locations, hot night indices are strongly associated with cause-specific deaths. Modeling the impact of thermal characteristics during summer nights on mortality could improve decisionmaking for preventive public health strategies.

Temperature-related effects on respiratory medical prescriptions in Spain.

BACKGROUND: The increased risk of mortality during periods of high and low temperatures has been well established. However, most of the studies used daily counts of deaths or hospitalisations as health outcomes, although they are the ones at the top of the health impact pyramid reflecting only a limited proportion of patients with the most severe cases. OBJECTIVES: This study evaluates the relationship between short-term exposure to the daily mean temperature and medication prescribed for the respiratory system in five Spanish cities. METHODS: We fitted time series regression models to cause-specific medical prescriptions, including different respiratory subgroups and age groups. We included a distributed lag non-linear model with lags up to 14 days for daily mean temperature. City-specific associations were summarised as overall-cumulative exposure-response curves. RESULTS: We found a positive association between cause-specific medical prescriptions and daily mean temperature with a non-linear inverted J- or V-shaped relationship in most cities. Between 0.3% and 0.6% of all respiratory prescriptions were attributed to cold for Madrid, Zaragoza and Pamplona, while in cities with only cold effects the attributable fractions were estimated as 19.2% for Murcia and 13.5% for Santander. Heat effects in Madrid, Zaragoza and Pamplona showed higher fractions between 8.7% and 17.2%. The estimated costs are in general higher for heat effects, showing annual values ranging between €191,905 and €311,076 for heat per 100,000 persons. CONCLUSIONS: This study provides novel evidence of the effects of the thermal environment on the prescription of medication for respiratory disorders in Spain, showing that low and high temperatures lead to an increase in the number of such prescriptions. The consumption of medication can reflect exposure to the environment with a lesser degree of severity in terms of morbidity.

Effects of circulation weather types on influenza hospital admissions in Spain.

In this study, we use a statistical approach based on generalized additive models, linking atmospheric circulation and the number of influenza-related hospital admissions in the Spanish Iberian Peninsula during 2003-2013. The relative risks are estimated for administrative units in the Spanish territory, which is politically structured into 15 regions called autonomous communities. A catalog of atmospheric circulation types is defined for this purpose. The relationship between the exposure and response variables is modeled using a distributed lag nonlinear model (DLNM). Types from southwest and anticyclonic are significant in terms of the probability of having more influenza-related hospital admissions for all of Spain. The heterogeneity of the results is very high. The relative risk is also estimated for each autonomous community and weather type, with the maximum number of influenza-related hospital admissions associated with circulation types from the southwest and the south. We identify six specific situations where relative risk is considered extreme and twelve with a high risk of increasing influenza-related hospital admissions. The rest of the situations present a moderate risk. Atmospheric local conditions become a key factor for understanding influenza spread in each spatial unit of the Peninsula. Further research is needed to understand how different weather variables (temperature, humidity, and sun radiation) interact and promote the spread of influenza.

Glossary on atmospheric electricity and its effects on biology.

There is an increasing interest to study the interactions between atmospheric electrical parameters and living organisms at multiple scales. So far, relatively few studies have been published that focus on possible biological effects of atmospheric electric and magnetic fields. To foster future work in this area of multidisciplinary research, here we present a glossary of relevant terms. Its main purpose is to facilitate the process of learning and communication among the different scientific disciplines working on this topic. While some definitions come from existing sources, other concepts have been re-defined to better reflect the existing and emerging scientific needs of this multidisciplinary and transdisciplinary area of research.

Comparison of temperature-mortality associations using observed weather station and reanalysis data in 52 Spanish cities.

BACKGROUND: Most studies use temperature observation data from weather stations near the analyzed region or city as the reference point for the exposure-response association. Climatic reanalysis data sets have already been used for climate studies, but are not yet used routinely in environmental epidemiology. METHODS: We compared the mortality-temperature association using weather station temperature and ERA-5 reanalysis data for the 52 provincial capital cities in Spain, using time-series regression with distributed lag non-linear models. RESULTS: The shape of temperature distribution is very close between the weather station and ERA-5 reanalysis data (correlation from 0.90 to 0.99). The overall cumulative exposure-response curves are very similar in their shape and risks estimates for cold and heat effects, although risk estimates for ERA-5 were slightly lower than for weather station temperature. CONCLUSIONS: Reanalysis data allow the estimation of the health effects of temperature, even in areas located far from weather stations or without any available.

Heat wave intensity and daily mortality in four of the largest cities of Spain.

In the current context of climate change, heat waves have become a significant problem for human health. This study assesses the effects of heat wave intensity on mortality (natural, respiratory and cardiovascular causes) in four of the largest cities of Spain (Barcelona, Bilbao, Madrid and Seville) during the period between 1990 and 2014. To model the heat wave severity the Excess Heat Factor (EHF) was used. The EHF is a two-component index. The first is the comparison of the three-day average daily mean temperature with the 95th percentile. The second component is a measure of the temperatures reached during the three-day period compared with the recent past (the previous 30 days). The city-specific exposure-response curves showed a non-linear J-shaped relationship between mortality and the EHF. Overall city-specific mortality risk estimates in natural causes for 1st vs. 99th percentile increases range from the highest mortality risk with 2.73 (95% CI: 2.34-3.18) in Seville to a risk of 1.78 (95% CI: 1.62-1.97) and 1.78 (95% CI: 1.45-2.19) in Barcelona and Bilbao, respectively. When we compare our results with risk estimates for the analyzed Spanish cities in other studies, the heat wave related mortality risks seem to be clearly higher. Furthermore, it has been demonstrated that different heat wave days of the same event do not present the same degree of severity/intensity. Thus, the intensity of a heat wave is an important mortality risk indicator during heat wave days. Due to the low number of studies on the EHF as a heat wave intensity indicator and heat-related mortality and morbidity, further research is required to validate its application in other geographic areas and focus populations.

A time series analysis of the relationship between apparent temperature, air pollutants and ischemic stroke in Madrid, Spain.

The understanding of the role of environment on the pathogenesis of stroke is gaining importance in the context of climate change. This study analyzes the temporal pattern of ischemic stroke (IS) in Madrid, Spain, during a 13-year period (2001-2013), and the relationship between ischemic stroke (admissions and deaths) incidence and environmental factors on a daily scale by using a quasi-Poisson regression model. To assess potential delayed and non-linear effects of air pollutants and Apparent Temperature (AT), a biometeorological index which represents human thermal comfort on IS, a lag non-linear model was fitted in a generalized additive model. The mortality rate followed a downward trend over the studied period, however admission rates progressively increased. Our results show that both increases and decreases in AT had a marked relationship with IS deaths, while hospital admissions were only associated with low AT. When analyzing the cumulative effects (for lag 0-14 days), with an AT of 1.7 °C (percentile 5%) a RR of 1.20 (95% CI, 1.05-1.37) for IS mortality and a RR of 1.09 (95% CI, 0.91-1.29) for morbidity is estimated. Concerning gender differences, men show higher risks of mortality in low temperatures and women in high temperatures. No significant relationship was found between air pollutant concentrations and IS morbi-mortality, but this result must be interpreted with caution, since there are strong spatial fluctuations of the former between nearby geographical areas that make it difficult to perform correlation analyses.

Short-term effects of heat and cold on respiratory drug use. A time-series epidemiological study in A Coruña, Spain.

The consumption of medication, especially over-the-counter drugs, can reflect environmental exposure with a lesser degree of severity in terms of morbidity. The non-linear effects of maximum and minimum apparent temperature on respiratory drug sales in A Coruña from 2006 to 2010 were examined using a distributed lag nonlinear model. In particular, low apparent temperatures proved to be associated with increased sales of respiratory drugs. The strongest consistent risk estimates were found for minimum apparent temperatures in respiratory drug sales with an increase of 33.4% (95% CI, 12.5%-58.0%) when the temperature changed from 2.8°C to -1.4 °C. These findings may serve to guide the planning of public health interventions to predict and manage the health effects of exposure to the thermal environment for lower degrees of morbidity. More precisely, significant increases in the use of measured over-the-counter medication could be used to identify and anticipate influenza outbreaks due to a more sensitive degree of the data source.

Kawasaki disease in Spanish paediatric population and synoptic weather types: an observational study.

Kawasaki disease (KD) is a vasculitis of unelucidated pathogenesis that usually occurs in paediatric patients. In this study we analyse the temporal pattern and geographical distribution of the disease in Spain, and its relationship with atmospheric circulation patterns. We performed a retrospective study in which we collected all hospital admissions due to KD in the country between 2005 and 2015 and explored their relationship with demographic and geographical characteristics. Moreover, we calculated daily surface atmospheric patterns over Spain to study the relationship between weather types (WT) and KD Admissions. The average admission rate for KD in the paediatric population was 3.90 per 100,000, with a male to female ratio of 1.56:1. The highest rate of admissions was found in the 0-4-year-old group, with an incidence of 11.7 cases per 100,000. Admissions followed an annual cyclic pattern with a peak of incidence in January (p = 0.022) and a nadir in September. There was an upwards trend in the number of KD admissions in male sex during the study period (p = 0.004). However, there were marked geographical differences in the incidence rate. Finally, the analysis of the relationship between the WT and the number of admissions by KD revealed no statistically significant association. KD admissions follow a peculiar seasonal and spatial distribution, that suggest the involvement of environmental factors in the disease; however, the absence of an association with WT should be interpreted with caution and regional studies should be done to explore this relationship.

Comparison of Air Pollution-Mortality Associations Using Observed Particulate Matter Concentrations and Reanalysis Data in 33 Spanish Cities.

Air pollution poses a health hazard in all countries. However, complete data on ambient particulate matter (PM) concentrations are not available in all world regions. Reanalysis data is already a valuable source of exposure data in epidemiological studies examining the relationship between temperature and health. Nevertheless, the performance of reanalysis data in assessing the short-term health effects of particulate air pollution remains unclear. We assessed the performance of CAMS reanalysis (EAC4) data from the European Centre for Medium-Range Weather Forecasts, compared with daily PM concentrations from field monitoring stations, to estimate short-term exposure to PM with an aerodynamic diameter less than 10 µm (PM10) on daily mortality in 33 Spanish provincial capital cities using a two-stage time series regression design. The shape of the PM10 distribution varied substantially between PM observations and CAMS global reanalysis of atmospheric composition (EAC4) reanalysis data, with correlation ranging from 0.21 to 0.58. The pooled mortality risk for a 10 µg/m3 increase in PM10 showed similar estimates using PM concentrations {relative risks (RR) = 1.007, 95% confidence intervals (95% CI) = [1.002, 1.011]} and EAC4 reanalysis data (RR = 1.011, 95% CI = [1.006, 1.015]). However, the city-specific PM10 beta coefficients estimated using PM concentrations and EAC4 reanalysis data showed a low correlation (r = 0.22). The use of reanalysis data should be approached with caution when assessing the association between particulate matter air pollution and health outcomes, particularly in cities with small populations.

Impact of population aging on future temperature-related mortality at different global warming levels.

Older adults are generally amongst the most vulnerable to heat and cold. While temperature-related health impacts are projected to increase with global warming, the influence of population aging on these trends remains unclear. Here we show that at 1.5 °C, 2 °C, and 3 °C of global warming, heat-related mortality in 800 locations across 50 countries/areas will increase by 0.5%, 1.0%, and 2.5%, respectively; among which 1 in 5 to 1 in 4 heat-related deaths can be attributed to population aging. Despite a projected decrease in cold-related mortality due to progressive warming alone, population aging will mostly counteract this trend, leading to a net increase in cold-related mortality by 0.1%-0.4% at 1.5-3 °C global warming. Our findings indicate that population aging constitutes a crucial driver for future heat- and cold-related deaths, with increasing mortality burden for both heat and cold due to the aging population.

Health and Economic Benefits of Complying With the World Health Organization Air Quality Guidelines for Particulate Matter in Nine Major Latin American Cities.

Objectives: This study aims to estimate the short-term preventable mortality and associated economic costs of complying with the World Health Organization (WHO) air quality guidelines (AQGs) limit values for PM10 and PM2.5 in nine major Latin American cities. Methods: We estimated city-specific PM-mortality associations using time-series regression models and calculated the attributable mortality fraction. Next, we used the value of statistical life to calculate the economic benefits of complying with the WHO AQGs limit values. Results: In most cities, PM concentrations exceeded the WHO AQGs limit values more than 90% of the days. PM10 was found to be associated with an average excess mortality of 1.88% with concentrations above WHO AQGs limit values, while for PM2.5 it was 1.05%. The associated annual economic costs varied widely, between US$ 19.5 million to 3,386.9 million for PM10, and US$ 196.3 million to 2,209.6 million for PM2.5. Conclusion: Our findings suggest that there is an urgent need for policymakers to develop interventions to achieve sustainable air quality improvements in Latin America. Complying with the WHO AQGs limit values for PM10 and PM2.5 in Latin American cities would substantially benefits for urban populations.

Mortality burden and economic loss attributable to cold and heat in Central and South America.

Background: We quantify the mortality burden and economic loss attributable to nonoptimal temperatures for cold and heat in the Central and South American countries in the Multi-City Multi-Country (MCC) Collaborative Research Network. Methods: We collected data for 66 locations from 13 countries in Central and South America to estimate location-specific temperature-mortality associations using time-series regression with distributed lag nonlinear models. We calculated the attributable deaths for cold and heat as the 2.5th and 97.5th temperature percentiles, above and below the minimum mortality temperature, and used the value of a life year to estimate the economic loss of delayed deaths. Results: The mortality impact of cold varied widely by country, from 9.64% in Uruguay to 0.22% in Costa Rica. The heat-attributable fraction for mortality ranged from 1.41% in Paraguay to 0.01% in Ecuador. Locations in arid and temperate climatic zones showed higher cold-related mortality (5.10% and 5.29%, respectively) than those in tropical climates (1.71%). Arid and temperate climatic zones saw lower heat-attributable fractions (0.69% and 0.58%) than arid climatic zones (0.92%). Exposure to cold led to an annual economic loss of $0.6 million in Costa Rica to $472.2 million in Argentina. In comparison, heat resulted in economic losses of $0.05 million in Ecuador to $90.6 million in Brazil. Conclusion: Most of the mortality burden for Central and South American countries is caused by cold compared to heat, generating annual economic losses of $2.1 billion and $290.7 million, respectively. Public health policies and adaptation measures in the region should account for the health effects associated with nonoptimal temperatures.

Impacts of land-use and land-cover changes on temperature-related mortality.

Background: Land-use and land-cover change (LULCC) can substantially affect climate through biogeochemical and biogeophysical effects. Here, we examine the future temperature-mortality impact for two contrasting LULCC scenarios in a background climate of low greenhouse gas concentrations. The first LULCC scenario implies a globally sustainable land use and socioeconomic development (sustainability). In the second LULCC scenario, sustainability is implemented only in the Organisation for Economic Cooperation and Development countries (inequality). Methods: Using the Multi-Country Multi-City (MCC) dataset on mortality from 823 locations in 52 countries and territories, we estimated the temperature-mortality exposure-response functions (ERFs). The LULCC and noLULCC scenarios were implemented in three fully coupled Earth system models (ESMs): Community Earth System Model, Max Planck Institute Earth System Model, and European Consortium Earth System Model. Next, using temperature from the ESMs' simulations and the estimated location-specific ERFs, we assessed the temperature-related impact on mortality for the LULCC and noLULCC scenarios around the mid and end century. Results: Under sustainability, the multimodel mean changes in excess mortality range from -1.1 to +0.6 percentage points by 2050-2059 across all locations and from -1.4 to +0.5 percentage points by 2090-2099. Under inequality, these vary from -0.7 to +0.9 percentage points by 2050-2059 and from -1.3 to +2 percentage points by 2090-2099. Conclusions: While an unequal socioeconomic development and unsustainable land use could increase the burden of heat-related mortality in most regions, globally sustainable land use has the potential to reduce it in some locations. However, the total (cold and heat) impact on mortality is very location specific and strongly depends on the underlying climate change scenario due to nonlinearity in the temperature-mortality relationship.

Seasonality of mortality under climate change: a multicountry projection study.

BACKGROUND: Climate change can directly impact temperature-related excess deaths and might subsequently change the seasonal variation in mortality. In this study, we aimed to provide a systematic and comprehensive assessment of potential future changes in the seasonal variation, or seasonality, of mortality across different climate zones. METHODS: In this modelling study, we collected daily time series of mean temperature and mortality (all causes or non-external causes only) via the Multi-Country Multi-City Collaborative (MCC) Research Network. These data were collected during overlapping periods, spanning from Jan 1, 1969 to Dec 31, 2020. We projected daily mortality from Jan 1, 2000 to Dec 31, 2099, under four climate change scenarios corresponding to increasing emissions (Shared Socioeconomic Pathways [SSP] scenarios SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5). We compared the seasonality in projected mortality between decades by its shape, timings (the day-of-year) of minimum (trough) and maximum (peak) mortality, and sizes (peak-to-trough ratio and attributable fraction). Attributable fraction was used to measure the burden of seasonality of mortality. The results were summarised by climate zones. FINDINGS: The MCC dataset included 126 809 537 deaths from 707 locations within 43 countries or areas. After excluding the only two polar locations (both high-altitude locations in Peru) from climatic zone assessments, we analysed 126 766 164 deaths in 705 locations aggregated in four climate zones (tropical, arid, temperate, and continental). From the 2000s to the 2090s, our projections showed an increase in mortality during the warm seasons and a decrease in mortality during the cold seasons, albeit with mortality remaining high during the cold seasons, under all four SSP scenarios in the arid, temperate, and continental zones. The magnitude of this changing pattern was more pronounced under the high-emission scenarios (SSP3-7.0 and SSP5-8.5), substantially altering the shape of seasonality of mortality and, under the highest emission scenario (SSP5-8.5), shifting the mortality peak from cold seasons to warm seasons in arid, temperate, and continental zones, and increasing the size of seasonality in all zones except the arid zone by the end of the century. In the 2090s compared with the 2000s, the change in peak-to-trough ratio (relative scale) ranged from 0·96 to 1·11, and the change in attributable fraction ranged from 0·002% to 0·06% under the SSP5-8.5 (highest emission) scenario. INTERPRETATION: A warming climate can substantially change the seasonality of mortality in the future. Our projections suggest that health-care systems should consider preparing for a potentially increased demand during warm seasons and sustained high demand during cold seasons, particularly in regions characterised by arid, temperate, and continental climates. FUNDING: The Environment Research and Technology Development Fund of the Environmental Restoration and Conservation Agency, provided by the Ministry of the Environment of Japan.