Research ArticleCLIMATOLOGY

The emergence of heat and humidity too severe for human tolerance

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Science Advances  08 May 2020:
Vol. 6, no. 19, eaaw1838
DOI: 10.1126/sciadv.aaw1838
  • Fig. 1 Observed global extreme humid heat.

    Color symbols represent the 99.9th percentile of observed daily maximum TW for 1979–2017 for HadISD stations with at least 50% data availability over this period. Marker size is inversely proportional to station density.

  • Fig. 2 Global trends in extreme humid heat.

    (A to D) Annual global counts of TW exceedances above the thresholds labeled on the respective panel, from HadISD (black, right axes, with units of station days) and ERA-Interim grid points (gray, left axes, with units of grid-point days). We consider only HadISD stations with at least 50% data availability over 1979–2017. Correlations between the series are annotated in the top left of each panel, and dotted lines highlight linear trends. (E) Annual global maximum TW in ERA-Interim. (F) The line plot shows global mean annual temperature anomalies (relative to 1850–1879) according to HadCRUT4 (40), which we use to approximate each year’s observed warming since preindustrial; circles indicate HadISD station occurrences of TW exceeding 35°C, with radius linearly proportional to global annual count, measured in station days.

  • Fig. 3 Monsoon-modulated seasonality of extreme humid heat.

    (A) Early monsoon areas (light orange shading; <June 15 average onset date) and late monsoon areas (green shading; ≥June 15 average onset date) in South Asia. (B) (Solid line) Mean annual number of TW exceedances of 31°C per station, by pentad, in the early monsoon areas. (Dashed line) Mean relative humidity associated with these exceedances. The division between the brown- and blue-shaded sections represents the station-weighted-average climatological monsoon onset date. (C) Same as in (B), but for the late monsoon areas.

  • Fig. 4 Projections of extreme humid heat exceeding the physiological survivability limit.

    (A) Shading shows the amount of global warming (since preindustrial) until TW = 35°C is projected to become at least a 1-in-30-year event at each grid cell according to a nonstationary GEV model. In blank areas, more than 4°C of warming is necessary. Black dots indicate ERA-Interim grid cells with a maximum TW (1979–2017) in the hottest 0.1% of grid cells worldwide. (B) Total area with TW of at least 35°C, as a function of mean annual temperature change 〈T〉 from the preindustrial period. Red (green) vertical lines highlight the lowest 〈T〉 for which there are nonzero areas over land (sea)—the respective ToE. (C) Bootstrap estimates of the ToE. See text for details of this definition and calculation.

  • Fig. 5 Trends and maxima of observed SST.

    (A) Annual maximum of monthly SST across all grid cells in the HadISST dataset; orange dashed line is a running 30-year average, and red line marks 35°C. (B) All-time maximum SST around the Persian Gulf and Arabian Sea. The blue points mark locations where monthly mean SST rose above 35°C in 2017.

Supplementary Materials

  • Supplementary Materials

    The emergence of heat and humidity too severe for human tolerance

    Colin Raymond, Tom Matthews, Radley M. Horton

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