Understanding Heat Stress and Preparing for the Future

Tuesday, January 5, 2016

How the number of days above an extreme wet-bulb temperature changed by the 2060s. Credit: Ethan Coffel

The work of Ethan Coffel, NE CSC Graduate Fellow at Columbia University was featured in several news outlets following the American Geophysical Union (AGU) annual meeting in San Fransisco.  By later this century, parts of the world where the population is expected to rise the most will experience an increase in the worst heat events — 

those where sky-high temperatures combine with oppressive humidity to hit the limits of the human capacity to cope.  Ethan presented his findings at the AGU meeting in December. 
“As the humidity climbs, you lose the ability to cool yourself — pretty quickly, actually,” Ethan said. Young children, the elderly and the infirm are particularly vulnerable to these heat stress events. Research has suggested that there’s a threshold to what even a healthy human body can handle, defined by a measure of both temperature and humidity called the wet-bulb temperature. A wet-bulb temperature of 95°F (35°C) is thought to be the limit of what is endurable when a person is sitting in the shade and at rest. Essentially it’s the point where sweat stops evaporating, and “is basically unheard of” in today’s climate, Ethan said.
Ethan and colleagues used climate models to estimate how much more often the worst heat stress events of a recent period (1985-2005) would occur by the 2060s all over the globe, as well as how many times per year certain wet-bulb thresholds might be hit. The largest increases came, unsurprisingly, in a band across the tropics, because conditions there don’t change as much throughout the year as they do in more temperate locations.
While lowering greenhouse gas emissions could delay the effects, Ethan said the findings point to the need for societies to adapt to such changes. Populations, particularly in developing countries, already struggle to deal with major heat waves because they lack access to simple measures like clean drinking water or cooling centers.
The researchers hope to explore more of the ways that extreme heat stress might tax society, including how it might interact with other factors like poor air quality, as well as what particular meteorological conditions are important for such events to come together to get a better understanding of how they might change in the future. Follow up work will explore the implications of these heat stress projections for large mammals in the Northeast U.S.
Figure at top:  How the number of days above an extreme wet-bulb temperature changed by the 2060s.
Credit: Ethan Coffel