Temporal Change in minimum mortality temperature under climate change: a multi-country multi-community observational study

BACKGROUND AND AIM: Minimum mortality temperature (MMT) and MMT percentile (MMTP) are important indicators for human adaptation to climate. Several studies reported that the MMT and MMTP have changed over time, but the changing direction has been heterogeneous over locations. We examined the temporal change of the MMT and MMTP in a global scale and investigated the heterogeneity over communi-ties, countries, regions, and climate zones. METHODS: Daily time-series data for mortality and ambient temperature for 699 communities in 34 countries from 1986 to 2015 were analyzed by a two-stage meta-analysis. First, we used a generalized linear model with quasi-Poisson distribution to estimate the MMT in each of the 5-year non-overlapping subperiods for each community. Then, we pooled the subperiod-specific MMTs over communities using mixed effects meta-regressions to estimate the temporal change of the MMT (1) for the whole population, (2) by climate zone, (3) by region and (4) by country. Moreover, we estimated the tem-poral change of the MMTP in the same way. RESULTS:The MMT and MMTP have decreased over the subperiods for the whole population (linear slope (LS)=-0.182, p-value (p) =0.184 for MMT; LS=-0.021, p=0.035 for MMTP). Such decreasing trends were more prominent in the temperate climate zone (LS=-0.268, p=0.042 for MMT; LS=-0.025, p=0.01) than in others (i.e., tropical, dry, and continental). Region-specifically, the decreasing trends were observed in North Europe, Central Europe, South Europe, South Africa, Middle-East Asia, South-East Asia and Australia while increasing trends were found in North America, Central Amer-ica, South America and East Asia. Country-specific results closely followed the region-specific re-sults. CONCLUSIONS:We found the MMT and the MMTP have decreased over time for the entire study population, but the changing direction was largely heterogeneous over climate zones, regions, and countries. Our results suggest that human adaptation may largely depend on regional and country-specific characteristics. KEYWORDS: Climate Change, Minimum Mortality Temperature, Adaptation, Heterogeneity