Researchers for the first time have calculated the highest tolerable "wet-bulb" temperature and found that this temperature could be exceeded for the first time in human history in future climate scenarios if greenhouse gas emissions continue at their current rate.
Wet-bulb temperature is equivalent to what is felt when wet skin is exposed to moving air. It includes temperature and atmospheric humidity and is measured by covering a standard thermometer bulb with a wetted cloth and fully ventilating it.
The researchers calculated that humans and most mammals, which have internal body temperatures near 98.6 degrees Fahrenheit, will experience a potentially lethal level of heat stress at wet-bulb temperature above 95 degrees sustained for six hours or more, said Matthew Huber, the Purdue professor of earth and atmospheric sciences who co-authored the paper that will be published in Thursday's (May 6) issue of the Proceedings of the National Academy of Sciences.
"Although areas of the world regularly see temperatures above 100 degrees, really high wet-bulb temperatures are rare," Huber said. "This is because the hottest areas normally have low humidity, like the 'dry heat' referred to in Arizona. When it is dry, we are able to cool our bodies through perspiration and can remain fairly comfortable. The highest wet-bulb temperatures ever recorded were in places like Saudi Arabia near the coast where winds occasionally bring extremely hot, humid ocean air over hot land leading to unbearably stifling conditions, which fortunately are short-lived today."
The study did not provide new evaluations of the likelihood of future climate scenarios, but explored the impacts of warming. The challenges presented by the future climate scenarios are daunting in their scale and severity, he said.
"Whole countries would intermittently be subject to severe heat stress requiring large-scale adaptation efforts," Huber said. "One can imagine that such efforts, for example the wider adoption of air conditioning, would cause the power requirements to soar, and the affordability of such approaches is in question for much of the Third World that would bear the brunt of these impacts. In addition, the livestock on which we rely would still be exposed, and it would make any form of outside work hazardous."
While the Intergovernmental Panel on Climate Change central estimates of business-as-usual warming by 2100 are seven degrees Fahrenheit, eventual warming of 25 degrees is feasible, he said.
"We found that a warming of 12 degrees Fahrenheit would cause some areas of the world to surpass the wet-bulb temperature limit, and a 21-degree warming would put half of the world's population in an uninhabitable environment," Huber said. "When it comes to evaluating the risk of carbon emissions, such worst-case scenarios need to be taken into account. It's the difference between a game of roulette and playing Russian roulette with a pistol. Sometimes the stakes are too high, even if there is only a small chance of losing."
Steven Sherwood, the professor at the Climate Change Research Centre at the University of New South Wales, Australia, who is the paper's lead author, said prolonged wet-bulb temperatures above 95 degrees would be intolerable after a matter of hours.
"The wet-bulb limit is basically the point at which one would overheat even if they were naked in the shade, soaking wet and standing in front of a large fan," Sherwood said. "Although we are very unlikely to reach such temperatures this century, they could happen in the next."
Humans at rest generate about 100 watts of energy from metabolic activity. Wet-bulb temperature estimates provide upper limits on the ability of people to cool themselves by sweating and otherwise dissipating this heat, he said. In order for the heat dissipation process to work, the surrounding air must be cooler than the skin, which must be cooler than the core body temperature. The cooler skin is then able to absorb excess heat from the core and release it into the environment. If the wet-bulb temperature is warmer than the temperature of the skin, metabolic heat cannot be released and potentially dangerous overheating can ensue depending on the magnitude and duration of the heat stress.
The National Science Foundation-funded research investigated the long-term implications of sustained greenhouse gas emissions on climate extremes. The team used climate models to compare the peak wet-bulb temperatures to the global temperatures for various climate simulations and found that the peak wet-bulb temperature rises approximately 1 degree Centigrade for every degree Centigrade increase in tropical mean temperature.
Huber did the climate modeling on supercomputers operated by Information Technology at Purdue (ITaP), Purdue's central information technology organization. Sherwood performed the wet-bulb calculations.
"These temperatures haven't been seen during the existence of hominids, but they did occur about 50 million years ago, and it is a legitimate possibility that the Earth could see such temperatures again," Huber said. "If we consider these worst-case scenarios early enough, perhaps we can do something to address the risk through mitigation or new technological advancements that will allow us to adapt."
Writers: Elizabeth K. Gardner, 765-494-2081, firstname.lastname@example.org
Greg Kline, 765-494-8167, email@example.com
Sources: Matthew Huber, 765-494-9531, firstname.lastname@example.org
Steven Sherwood, +61 (2) 9385 8960, email@example.com
Elizabeth K. Gardner | EurekAlert!
As sea level rises, much of Honolulu and Waikiki vulnerable to groundwater inundation
29.03.2017 | University of Hawaii at Manoa
Researchers discover dust plays prominent role in nutrients of mountain forest ecoystems
29.03.2017 | University of Wyoming
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
29.03.2017 | Materials Sciences
29.03.2017 | Physics and Astronomy
29.03.2017 | Earth Sciences