Threshold identified for climate conditions causing human mortality

Lethal climate conditions
Average daily air temperature and relative humidity during lethal heat events (black crosses) and during non-lethal heat event (the red to yellow shading indicates the number of such non-lethal events). The blue line separates lethal and non-lethal heatwave events. The red line is a conservative estimate beyond which all events were deadly.

In a new study documented global lethal heat events were used to identify the climatic conditions under which human death occurred.  The results were used to geographically  quantify the current  occurrence lethal climatic conditions worldwide. Papers published between 1980 and 2014 were reviewed and 783 cases of excess human mortality associated with heat from 164 cities in 36 countries were found. Based on the climatic conditions of the lethal heat events, a global threshold beyond which daily mean surface air temperature and relative humidity become deadly was identified.  It is estimated that about 30% of the world’s population is currently exposed to climatic conditions exceeding this deadly threshold for at least 20 days a year.  Global risk of deadly heat, C. Mora et al., Global risk of deadly heat, Nature Climate Change 2, doi:10.1038/nclimate3322, (2017)