In South Asia, research of 2017 at MIT suggests that by the end of this century climate change could lead to summer heat waves with levels of heat and humidity that exceed what humans can survive without protection.
The study shows these deadly heat waves could begin within as little as a few decades to strike regions of India, Pakistan, and Bangladesh, including the fertile Indus and Ganges river basins that produce much of the region’s food supply.
The study follows an earlier report by Eltahir and his team that looked at projected heat waves in the Persian Gulf region. While the number of extreme-heat days projected for that region was even worse than for South Asia, Eltahir says the impact in the latter area could be vastly more severe. That’s because while the Persian Gulf area has a relatively small, relatively wealthy population and little agricultural land, the areas likely to be hardest hit in northern India, Bangladesh, and southern Pakistan are home to 1.5 billion people. These areas are also among the poorest in the region, with much of the population dependent on subsistence farming that requires long hours of hard labor out in the open and unprotected from the sun.
While the projections show the Persian Gulf may become the region of the worst heat waves on the planet, northern India is a close second, Eltahir says, and eastern China, also densely populated, is third. The highest concentrations of heat in the Persian Gulf region would be seen over water and not land, unlike in the Indo-Gangetic plains where the brunt will be borne on inhabited land.
The new analysis is based on recent research showing that hot weather’s most deadly effects for humans comes from a combination of high temperature and high humidity, an index which is measured by a reading known as wet-bulb temperature. The internal temperature of the human body is maintained at 37 degrees Celsius, while the temperature on the surface is around 35 °C. Sweating is the key process to this constant temperature modulation and the ability for moisture to evaporate is affected by heat and humidity. At a wet-bulb temperature of 35 degrees Celsius, the human body cannot cool itself enough to survive more than a few hours.
A previous study of temperature and humidity records show that in today’s climate, wet-bulb temperatures have rarely exceeded about 31 C anywhere on Earth. While the earlier report from Eltahir and his colleagues showed that this survivability limit would start to be exceeded occasionally in the Persian Gulf region by the end of this century, actual readings there in the summer of 2015 showed that the 35-degree wet-bulb limit had almost been reached already, suggesting that such extremes could begin happening earlier than projected. The summer of 2015 also produced one of the deadliest heat waves in history in South Asia, killing an estimated 3,500 people in Pakistan and India.
The study shows that by century’s end, absent serious reductions in global emissions, the most extreme, heat waves would increase from wet-bulb temperatures of about 31 C to 34.2 C. “It brings us close to the threshold” of survivability, he says, and “anything in the 30s is very severe.”
In today’s climate, about 2 percent of the Indian population sometimes gets exposed to extremes of 32-degree wet-bulb temperatures. According to this study, by 2100 that will increase to about 70 percent of the population, and about 2 percent of the people will sometimes be exposed to the survivability limit of 35 degrees. And because the region is important agriculturally, it’s not just those directly affected by the heat who will suffer, Eltahir says: “With the disruption to the agricultural production, it doesn’t need to be the heat wave itself that kills people. Production will go down, so potentially everyone will suffer.”
Heat waves over the last decade have been seen to cause more mortality among urban rather than rural Indians. One of the reasons for this is the work routine of Indian farmers which keeps them indoors during the hottest hours of the day. In cities, on the other hand, heavy concentration of concrete and glass along with limited natural cover increases temperature, creating the heat-island effect. Studies have found that by 2100, cities could get up to as much as 8°C hotter than current levels! This, combined with the typically round-the-clock physical labour in cities, has caused heavily disproportionate mortality in cities rather than in the country side.
Studies looking at heat waves in Ahmedabad found that spikes in mortality correlate with spikes in temperature. The case has been made that the actual number could be much higher since the National Crime Record Bureau only records death by heat strokes as a heat wave-associated death. This could also be the reason for the huge discrepancy in the number of deaths associated with the disastrous 2003 heat wave that struck Europe and killed over 70,000 and the 2015 Indian heat wave in which 2,241 people died. Both the events were of comparable duration and intensity.
The decadal mean of daily maximum temperature for April and May in the 2010s is 40 to 42 degrees over large parts of India. In the 1950s, the area with this high temperature was limited to only a small spot in south-central India touching 41 degrees. The region with temperature over 40 degrees began to expand in the 1970s and 1980s. The region with temperatures exceeding 41 degrees has expanded, and a region with temperatures greater than 42 degrees has appeared in south-central India in the 2010s, the study has found.
But while the study provides a grim warning about what could happen, it is far from inevitable, Eltahir stresses. The study examined not just the “business as usual” case but also the effects under a moderate mitigation scenario, which showed that these dramatic, deadly effects can still be averted.
The study shows these deadly heat waves could begin within as little as a few decades to strike regions of India, Pakistan, and Bangladesh, including the fertile Indus and Ganges river basins that produce much of the region’s food supply.
The study follows an earlier report by Eltahir and his team that looked at projected heat waves in the Persian Gulf region. While the number of extreme-heat days projected for that region was even worse than for South Asia, Eltahir says the impact in the latter area could be vastly more severe. That’s because while the Persian Gulf area has a relatively small, relatively wealthy population and little agricultural land, the areas likely to be hardest hit in northern India, Bangladesh, and southern Pakistan are home to 1.5 billion people. These areas are also among the poorest in the region, with much of the population dependent on subsistence farming that requires long hours of hard labor out in the open and unprotected from the sun.
While the projections show the Persian Gulf may become the region of the worst heat waves on the planet, northern India is a close second, Eltahir says, and eastern China, also densely populated, is third. The highest concentrations of heat in the Persian Gulf region would be seen over water and not land, unlike in the Indo-Gangetic plains where the brunt will be borne on inhabited land.
The new analysis is based on recent research showing that hot weather’s most deadly effects for humans comes from a combination of high temperature and high humidity, an index which is measured by a reading known as wet-bulb temperature. The internal temperature of the human body is maintained at 37 degrees Celsius, while the temperature on the surface is around 35 °C. Sweating is the key process to this constant temperature modulation and the ability for moisture to evaporate is affected by heat and humidity. At a wet-bulb temperature of 35 degrees Celsius, the human body cannot cool itself enough to survive more than a few hours.
A previous study of temperature and humidity records show that in today’s climate, wet-bulb temperatures have rarely exceeded about 31 C anywhere on Earth. While the earlier report from Eltahir and his colleagues showed that this survivability limit would start to be exceeded occasionally in the Persian Gulf region by the end of this century, actual readings there in the summer of 2015 showed that the 35-degree wet-bulb limit had almost been reached already, suggesting that such extremes could begin happening earlier than projected. The summer of 2015 also produced one of the deadliest heat waves in history in South Asia, killing an estimated 3,500 people in Pakistan and India.
The study shows that by century’s end, absent serious reductions in global emissions, the most extreme, heat waves would increase from wet-bulb temperatures of about 31 C to 34.2 C. “It brings us close to the threshold” of survivability, he says, and “anything in the 30s is very severe.”
In today’s climate, about 2 percent of the Indian population sometimes gets exposed to extremes of 32-degree wet-bulb temperatures. According to this study, by 2100 that will increase to about 70 percent of the population, and about 2 percent of the people will sometimes be exposed to the survivability limit of 35 degrees. And because the region is important agriculturally, it’s not just those directly affected by the heat who will suffer, Eltahir says: “With the disruption to the agricultural production, it doesn’t need to be the heat wave itself that kills people. Production will go down, so potentially everyone will suffer.”
Heat waves over the last decade have been seen to cause more mortality among urban rather than rural Indians. One of the reasons for this is the work routine of Indian farmers which keeps them indoors during the hottest hours of the day. In cities, on the other hand, heavy concentration of concrete and glass along with limited natural cover increases temperature, creating the heat-island effect. Studies have found that by 2100, cities could get up to as much as 8°C hotter than current levels! This, combined with the typically round-the-clock physical labour in cities, has caused heavily disproportionate mortality in cities rather than in the country side.
Studies looking at heat waves in Ahmedabad found that spikes in mortality correlate with spikes in temperature. The case has been made that the actual number could be much higher since the National Crime Record Bureau only records death by heat strokes as a heat wave-associated death. This could also be the reason for the huge discrepancy in the number of deaths associated with the disastrous 2003 heat wave that struck Europe and killed over 70,000 and the 2015 Indian heat wave in which 2,241 people died. Both the events were of comparable duration and intensity.
The decadal mean of daily maximum temperature for April and May in the 2010s is 40 to 42 degrees over large parts of India. In the 1950s, the area with this high temperature was limited to only a small spot in south-central India touching 41 degrees. The region with temperature over 40 degrees began to expand in the 1970s and 1980s. The region with temperatures exceeding 41 degrees has expanded, and a region with temperatures greater than 42 degrees has appeared in south-central India in the 2010s, the study has found.
But while the study provides a grim warning about what could happen, it is far from inevitable, Eltahir stresses. The study examined not just the “business as usual” case but also the effects under a moderate mitigation scenario, which showed that these dramatic, deadly effects can still be averted.
Acknowledgement : sourced entirely from this article.
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