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Last Updated:: 04/08/2017
Parts of east to be 'too hot' for humans
A deadly combination of heat and humidity could by the end of the century leave vast areas of South Asia, including parts of northern and eastern India, too hot for human survival, scientists tracking climate change said today.
A group of Massachusetts Institute of Technology researchers who have simulated temperature and moisture changes in conditions of unrestrained global warming have detected the highest risk around the densely populated regions along the Ganga and the Indus rivers.
Their study, published in the journal Science Advances on Wednesday, has found that by the end of the century, the combined heat-and-humidity conditions will exceed human "survivability threshold" in regions around the Chhotanagpur plateau, eastern India and Bangladesh.
"The combination of severe hazard from extreme heat waves and the acute vulnerability of a large population across South Asia maximises the risk from climate change impacts," said MIT professor of environmental engineering Elfatih Eltahir who led the study.
The study is one of the first to use computer simulations to predict changes in wet-bulb temperatures (TW), a measure that combines heat and humidity.
The TW value is always equal to or lower than the actual temperature, and the maximum TW rarely exceeds 31°C under current climate conditions. While a TW value below 35°C is still dangerous for most people, scientists believe a TW of 35°C should be considered an upper limit for human survivability in an environment that is not air-conditioned.
"A perfectly healthy adult exposed to a TW value of 35 degrees for about six hours has very little chance of survival even under shaded, well-ventilated conditions," Eltahir said. "For people who are already ill or for the very young or elderly, the survivability TW is possibly even lower."
Previous studies and observations have pointed to a rising trend in the frequency of heat waves in South Asia. Heat waves struck Odisha in 1998, Andhra Pradesh in 2003 and Gujarat in 2010. The fifth-deadliest heat wave in recorded history affected large parts of India and Pakistan in 2015, claiming over 3,500 lives.
The simulations predict that the TW will exceed 35°C on the Chhotanagpur plateau, eastern India, and Bangladesh and approach 35°C over most of South Asia by the end of the century under a climate change scenario where the global temperature rises by 4.5°C by 2100.
"But this is avoidable through global, regional and national actions to check global warming," Eltahir said.
Still, even under the lower global temperature rise of 2.25°C, Eltahir and his colleagues said, vast regions of South Asia are likely to experience TW episodes exceeding 31°C, which is "considered extremely dangerous" for most humans.
The study puts Lucknow and Patna among South Asian cities where the TW "reaches and exceeds" the survivability threshold of 35°C under the 4.5°C global warming scenario.This is a good scientific simulation; it tells us that South Asia needs to prepare for drastically reduced human comfort index levels," said Krishnan Raghavan, a climate change scientist at the Indian Institute of Tropical Meteorology, Pune, who was not associated with the study.
While earlier studies had independently probed changes in temperature and rainfall under various climate change scenarios, Krishnan said, it was important to factor in the effects of heat and moisture.
The Indian subcontinent is hemmed in by oceans on three sides and has vast cultivated areas and river basins, all of which contribute to moisture.
Scientists believe that applying TW values to assess heat stress in such regions is more meaningful than just predicting temperature trends. "Humans are very sensitive to the temperature and humidity, or mugginess," said Eun-Soon Im, assistant professor at the Hong Kong University of Science and Technology who was a member of the study team.
An increase in TW reduces the difference between the skin temperature and the body's inner temperature, lowering the body's ability to cool itself. The normal human body temperature lies within about 1°C of 37°C or 98.6°F, and any disruption in the body's ability to regulate its temperature within that narrow range may quickly cause harm. The risk of illness and death from extreme heat will be even more exacerbated for populations without access to air-conditioning, the researchers said.
They added that their findings might pose a "significant dilemma for India" because of the added health risks to its vulnerable populations.
Source: The Telegraph