People have some ability to adapt to their local climate type, but both cold and hot temperatures are still associated with increased risk of mortality. Public health strategies to alleviate the impact of ambient temperatures are important, in particular in the context of climate change.

Background:The evidence and method are limited for the associations between mortality and temperature variability (TV) within or between days.Objectives:We developed a novel method to calculate TV and investigated TV-mortality associations using a large multicountry data set.Methods:We collected daily data for temperature and mortality from 372 locations in 12 countries/regions (Australia, Brazil, Canada, China, Japan, Moldova, South Korea, Spain, Taiwan, Thailand, the United Kingdom, and the United States). We calculated TV from the standard deviation of the minimum and maximum temperatures during the exposure days. Two-stage analyses were used to assess the relationship between TV and mortality. In the first stage, a Poisson regression model allowing over-dispersion was used to estimate the community-specific TV-mortality relationship, after controlling for potential confounders. In the second stage, a meta-analysis was used to pool the effect estimates within each country.Results:There was a significant association between TV and mortality in all countries, even after controlling for the effects of daily mean temperature. In stratified analyses, TV was still significantly associated with mortality in cold, hot, and moderate seasons. Mortality risks related to TV were higher in hot areas than in cold areas when using short TV exposures (0–1 days), whereas TV-related mortality risks were higher in moderate areas than in cold and hot areas when using longer TV exposures (0–7 days).Conclusions:The results indicate that more attention should be paid to unstable weather conditions in order to protect health. These findings may have implications for developing public health policies to manage health risks of climate change.Citation:Guo Y, Gasparrini A, Armstrong BG, Tawatsupa B, Tobias A, Lavigne E, Coelho MS, Pan X, Kim H, Hashizume M, Honda Y, Guo YL, Wu CF, Zanobetti A, Schwartz JD, Bell ML, Overcenco A, Punnasiri K, Li S, Tian L, Saldiva P, Williams G, Tong S. 2016. Temperature variability and mortality: a multi-country study. Environ Health Perspect 124:1554–1559; http://dx.doi.org/10.1289/EHP149

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OBJECTIVE To assess short term mortality risks and excess mortality associated with exposure to ozone in several cities worldwide. DESIGNTwo stage time series analysis.SETTING 406 cities in 20 countries, with overlapping periods between 1985 and 2015, collected from the database of Multi-City Multi-Country Collaborative Research Network. POPULATIONDeaths for all causes or for external causes only registered in each city within the study period. MAIN OUTCOME MEASURESDaily total mortality (all or non-external causes only). RESULTSA total of 45 165 171 deaths were analysed in the 406 cities. On average, a 10 µg/m 3 increase in ozone during the current and previous day was associated with an overall relative risk of mortality of 1.0018 (95% confidence interval 1.0012 to 1.0024). Some heterogeneity was found across countries, with estimates ranging from greater than 1.0020 in the United Kingdom, South Africa, Estonia, and Canada to less than 1.0008 in Mexico and Spain. Short term excess mortality in association with exposure to ozone higher than maximum background levels (70 µg/ m 3 ) was 0.26% (95% confidence interval 0.24% to 0.28%), corresponding to 8203 annual excess deaths (95% confidence interval 3525 to 12 840) across the 406 cities studied. The excess remained at 0.20% (0.18% to 0.22%) when restricting to days above the WHO guideline (100 µg/m 3 ), corresponding to 6262 annual excess deaths (1413 to 11 065). Above more lenient thresholds for air quality standards in Europe, America, and China, excess mortality was 0.14%, 0.09%, and 0.05%, respectively. CONCLUSIONSResults suggest that ozone related mortality could be potentially reduced under stricter air quality standards. These findings have relevance for the implementation of efficient clean air interventions and mitigation strategies designed within national and international climate policies.Cite this as: BMJ 2020;368:m108 http://dx. WHAT IS ALREADY KNOWN ON THIS TOPICStudies on the short term association between ground level ozone and mortality have been mostly performed in a few locations, in limited geographical areas, and using various designs and modelling approaches Although most of the studies found positive associations, results are heterogeneous, and a critical comparison across different countries and regions is made difficult by the limited statistical power and differences across studies Estimates of the association are usually reported as relative risks, a summary measure that does not quantify the actual health impact and makes it difficult to evaluate comparative health benefits of different regulatory limits WHAT THIS STUDY ADDSThis large multi-country study found increased mortality risks associated with exposure to ozone across locations and countries, with an average 0.18% per 10 µg/m3, reinforcing the evidence of a potential causal association Risk estimates were translated in measures of excess mortality, and it was found that more than 6000 deaths each year, corresponding to 0.20% of the total mortality, would have been avoided in the...