Climate change affects human health, however, there have been no large-scale, systematic efforts to quantify the heat-related human health impacts that have already occurred due to climate change. Here we use empirical data from 732 locations in 43 countries to estimate the mortality burdens associated with the additional heat exposure that has resulted from recent human-5 induced warming, during the period 1991-2018. Across all study countries, we find that 37.0% (range 20.5-76.3%) of heat-related deaths can be attributed to anthropogenic climate change, and that increased mortality is evident on every continent. Burdens varied geographically, but were on the order of dozens to hundreds of deaths per year in many locations. Our findings support the urgent need for more ambitious mitigation and adaptation strategies to minimize the public 10 health impacts of climate change.

Background Exposure to cold or hot temperatures is associated with premature deaths. We aimed to evaluate the global, regional, and national mortality burden associated with non-optimal ambient temperatures. MethodsIn this modelling study, we collected time-series data on mortality and ambient temperatures from 750 locations in 43 countries and five meta-predictors at a grid size of 0•5° × 0•5° across the globe. A three-stage analysis strategy was used. First, the temperature-mortality association was fitted for each location by use of a time-series regression. Second, a multivariate meta-regression model was built between location-specific estimates and meta-predictors. Finally, the grid-specific temperature-mortality association between 2000 and 2019 was predicted by use of the fitted metaregression and the grid-specific meta-predictors. Excess deaths due to non-optimal temperatures, the ratio between annual excess deaths and all deaths of a year (the excess death ratio), and the death rate per 100 000 residents were then calculated for each grid across the world. Grids were divided according to regional groupings of the UN Statistics Division. FindingsGlobally, 5 083 173 deaths (95% empirical CI [eCI] 4 087 967-5 965 520) were associated with non-optimal temperatures per year, accounting for 9•43% (95% eCI 7•58-11•07) of all deaths (8•52% [6•19-10•47] were coldrelated and 0•91% [0•56-1•36] were heat-related). There were 74 temperature-related excess deaths per 100 000 residents (95% eCI 60-87). The mortality burden varied geographically. Of all excess deaths, 2 617 322 (51•49%) occurred in Asia. Eastern Europe had the highest heat-related excess death rate and Sub-Saharan Africa had the highest cold-related excess death rate. From 2000-03 to 2016-19, the global cold-related excess death ratio changed by -0•51 percentage points (95% eCI -0•61 to -0•42) and the global heat-related excess death ratio increased by 0•21 percentage points (0•13-0•31), leading to a net reduction in the overall ratio. The largest decline in overall excess death ratio occurred in South-eastern Asia, whereas excess death ratio fluctuated in Southern Asia and Europe.Interpretation Non-optimal temperatures are associated with a substantial mortality burden, which varies spatiotemporally. Our findings will benefit international, national, and local communities in developing preparedness and prevention strategies to reduce weather-related impacts immediately and under climate change scenarios.

Studies have pointed out that air pollution may be a contributing factor to the coronavirus disease 2019 (COVID-19) pandemic. However, the specific links between air pollution and severe acute respiratory syndrome-coronavirus-2 infection remain unclear. Here we provide evidence from in vitro, animal and human studies from the existing literature. Epidemiological investigations have related various air pollutants to COVID-19 morbidity and mortality at the population level, however, those studies suffer from several limitations. Air pollution may be linked to an increase in COVID-19 severity and lethality through its impact on chronic diseases, such as cardiopulmonary diseases and diabetes. Experimental studies have shown that exposure to air pollution leads to a decreased immune response, thus facilitating viral penetration and replication. Viruses may persist in air through complex interactions with particles and gases depending on: 1) chemical composition; 2) electric charges of particles; and 3) meteorological conditions such as relative humidity, ultraviolet (UV) radiation and temperature. In addition, by reducing UV radiation, air pollutants may promote viral persistence in air and reduce vitamin D synthesis. Further epidemiological studies are needed to better estimate the impact of air pollution on COVID-19. In vitro and in vivo studies are also strongly needed, in particular to more precisely explore the particle–virus interaction in air.

Background Many regions of the world are now facing more frequent and unprecedentedly large wildfires. However, the association between wildfire-related PM 2•5 and mortality has not been well characterised. We aimed to comprehensively assess the association between short-term exposure to wildfire-related PM 2•5 and mortality across various regions of the world.Methods For this time series study, data on daily counts of deaths for all causes, cardiovascular causes, and respiratory causes were collected from 749 cities in 43 countries and regions during 2000-16. Daily concentrations of wildfirerelated PM 2•5 were estimated using the three-dimensional chemical transport model GEOS-Chem at a 0•25° × 0•25° resolution. The association between wildfire-related PM 2•5 exposure and mortality was examined using a quasi-Poisson time series model in each city considering both the current-day and lag effects, and the effect estimates were then pooled using a random-effects meta-analysis. Based on these pooled effect estimates, the population attributable fraction and relative risk (RR) of annual mortality due to acute wildfire-related PM 2•5 exposure was calculated.Findings 65•6 million all-cause deaths, 15•1 million cardiovascular deaths, and 6•8 million respiratory deaths were included in our analyses. The pooled RRs of mortality associated with each 10 µg/m³ increase in the 3-day moving average (lag 0-2 days) of wildfire-related PM 2•5 exposure were 1•019 (95% CI 1•016-1•022) for all-cause mortality, 1•017 (1•012-1•021) for cardiovascular mortality, and 1•019 (1•013-1•025) for respiratory mortality. Overall, 0•62% (95% CI 0•48-0•75) of all-cause deaths, 0•55% (0•43-0•67) of cardiovascular deaths, and 0•64% (0•50-0•78) of respiratory deaths were annually attributable to the acute impacts of wildfire-related PM 2•5 exposure during the study period.Interpretation Short-term exposure to wildfire-related PM 2•5 was associated with increased risk of mortality. Urgent action is needed to reduce health risks from the increasing wildfires.