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THE BIG HEAT

The IPCC report predicts that South Asia will swing from droughts to floods

A boy plays in the flooded street after heavy monsoon rains triggered flooding at Kutapalong refugee camp in Bangladesh
OMAR'S FILM SCHOOL / REUTERS
A flood of suffering to come.
  • Samanth Subramanian
By Samanth Subramanian

Looking into the Future of Capitalism

Published

Man-made climate change will set off intense, frequent heatwaves in South Asia over the coming decades, according to a new report from the Intergovernmental Panel on Climate Change (IPCC). In tandem, the report said, the monsoon will strengthen over the subcontinent, leading to rain-fed flooding and humid heat stress, a combination of high temperature and moisture.

The deluges may not begin immediately. In a regional quirk, the aerosols emitted by South Asia—particles from emissions, or stirred-up dust—are thought to have had the opposite effect over the second half of the 20th century, drying out the monsoon and triggering droughts. But by the end of the 21st century, the IPCC reported with what it called a high degree of confidence, greenhouse gases and the heat they trap will have their effects. The rain will multiply; at the same time, the monsoon will turn less predictable year to year, making it harder to prepare for its consequences.

Climate change will make India both hotter and more humid

Just as the increase in rainfall will make the subcontinent more humid, the increase in temperature will result in more “extreme heat episodes.” The IPCC report predicts many parts of South Asia will cross the dangerous 41°C (106°F) threshold temperature more and more frequently. In the most extreme case of warming, the temperature will exceed 41°C on between 50-150 days more than it does at present.

The combination of heat and moisture results in higher “wet bulb temperatures,” which factor in ordinary, “dry bulb” temperature as well as humidity. On a day with 40°C ambient temperature and 64% humidity, the wet bulb temperature would be 34°C; if the humidity were just 40% on the same day, though, the wet bulb temperature would drop to 28°C.

Scientists think that a wet bulb temperature of 32°C makes it unsafe for people to work outdoors—a bleak sign for South Asia, where hundreds of millions of people labor without shelter. At a wet bulb temperature of 35°C, the human body struggles to cool itself.

If South Asia experiences 2°C of warming above pre-industrial levels, its population’s exposure to lethal wet bulb temperatures will rise 2.7 times, according to a study published by the American Geophysical Union earlier this year. “Even at 1.5 degrees, South Asia will have serious consequences in terms of heat stress,” said Moetasim Ashfaq, a scientist at the Oak Ridge National Laboratory in Tennessee.

Industrial productivity will wilt in the heat as well. Worker productivity drops between 2% and 4% per degree Celsius rise in temperature on a hot day, a recent study revealed. In the most extreme cases, a one-degree rise in average temperature over 10 days raised the probability of a garment worker being absent by 10% and of steel workers by 2%. As a result of these effects, if the daily average temperature rises by one degree, the annual output of a factory will fall by 2.1% over the year.

The Indian government has estimated that temperatures in the country could rise by as much as 4.4°C by 2100. India’s climate change strategy includes a commitment to slash the emissions intensity of its GDP by 33-35% by 2030, as compared to its 2005 levels. The strategy will help keep warming to 2°C of pre-industrial levels, according to an independent analysis, but it won’t meet the Paris Agreement’s long-term warming limit of 1.5°C.

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