[MCN] On getting braced for summer heat

[Lance Olsen]

Earth’s Future  -  An open access journal by the American Geophysical Union.
Accepted article
Accepted, unedited articles published online and citable. The final edited and typeset version of record will appear in future. 

Recent very hot summers in northern hemispheric land areas measured by wet bulb globe temperature will be the norm within 20 years 

Chao Li1,2, Xuebin Zhang3 , Francis Zwiers1 , Yuanyuan Fang2 , and Anna Michalak2 

1 Pacific Climate Impacts Consortium, University of Victoria, Victoria, British Columbia, V8W 2Y2, Canada. 
2 Department of Global Ecology, Carnegie Institution for Science, Stanford, California, 94305, USA. 
3 Climate Data and Analysis Section, Climate Research Division, Environment and Climate Change Canada, Toronto, Ontario, M3H 5T4, Canada. 

 Key Points: 
• Human influence has increased summer wet bulb globe temperature (WBGT) 
• Summer WBGT greater than the 1973-2012 record is now at least 70 times as likely 
• The 1973-2013 summer WBGT records will be the norm within 20 years. 

Abstract [Open access]
http://onlinelibrary.wiley.com/doi/10.1002/2017EF000639/abstract <http://onlinelibrary.wiley.com/doi/10.1002/2017EF000639/abstract>

Wet bulb Globe Temperature (WBGT) accounts for the effect of environmental temperature and humidity on thermal comfort, and can be directly related to the ability of the human body to dissipate excess metabolic heat and thus avoid heat stress. Using WBGT as a measure of environmental conditions conducive to heat stress, we show that anthropogenic influence has very substantially increased the likelihood of extreme high summer mean WBGT in northern hemispheric land areas relative to the climate that would have prevailed in the absence of anthropogenic forcing. We estimate that the likelihood of summer mean WGBT exceeding the observed historical record value has increased by a factor of at least 70 at regional scales due to anthropogenic influence on the climate. We further estimate that, in most northern hemispheric regions, these changes in the likelihood of extreme summer mean WBGT are roughly an order of magnitude larger than the corresponding changes in the likelihood of extreme hot summers as simply measured by surface air temperature. Projections of future summer mean WBGT under the RCP8.5 emissions scenario that are constrained by observations indicate that by 2030s at least 50% of the summers will have mean WBGT higher than the observed historical record value in all the analyzed regions, and that this frequency of occurrence will increase to 95% by mid-century. 
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"All organisms live within a limited range of body temperatures."

Hans O. Pörtner and Anthony P. Farrell. Physiology and Climate Change. 
SCIENCE 31 OCTOBER 2008
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“  … organisms have a physiological response to temperature, and these responses have important consequences."

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“Climate change impacts have now been documented across every ecosystem on Earth, despite an average warming of only ~1°C so far."

Scheffers et al. The broad footprint of climate change from genes to biomes to people. 
Science, 11 NOVEMBER 2016

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