Extreme heat is devastating the health and livelihoods of tens of millions in South Asia — and it’s only getting worse, according to experts.

Scientists warn that if global greenhouse gas emissions continue to rise at the current clip, heat and humidity levels in India will make it entirely uninhabitable, reports The New York Times.

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“These cities are going to become unlivable unless urban governments put in systems of dealing with this phenomenon and make people aware,” said Sujata Saunik, who served as a senior official in the Indian Ministry of Home Affairs and is now a fellow at the Harvard University School of Public Health, in an interview with the Times. “It’s a major public health challenge.”

Extreme heat can kill, as it did in Pakistan in May when more than 65 residents living in poverty succumbed to temperatures of 111 degrees Fahrenheit during Ramadan, reported Newsweek.

But as many of South Asia’s sweltering cities grow even hotter, scientists and economists are say that extreme heat is also devastating the health and livelihoods of tens of millions more, according to the Times report.

Street vendors, pedicab drivers, construction laborers, and anyone else exposed to the outdoors for six hours or more are increasingly in need of medical attention, due to stomach pains, migraines, fatigue, and other issues — all causing them to miss work and daily wages.

If things continue at the current rate, extreme heat could lead to a $2 trillion loss in labor productivity worldwide by 2030, the International Labor Organization recently estimated.

Climate change could sharply diminish living conditions for up to 800 million people in South Asia if nothing is done to reduce global greenhouse gas emissions, the World Bank warned in a study released in June.

This is particularly prescient for India: Among the 100 most populous cities where summer highs are expected to reach at least 95 degrees Fahrenheit by 2050, 24 are in India, according to estimates by the Urban Climate Change Research Network.

And approximately 38,000 extra deaths are projected to occur each year worldwide between 2030 and 2050, due to heat stress linked to climate change, according to the World Health Organization.

In India, local governments in some cities have already responded to concerns by painting tin roofs with reflective white paint in poor neighborhoods and distributing free bottled water during the hotter months. But long-term solutions are still needed, as those with access to air conditioning are few, and the machines themselves emit additional hot air back onto the street only adding to the stressful environs.