Extreme heat can kill, as it did by the dozens in Pakistan in May. But as many of South Asias already-scorching cities get even hotter, scientists and economists are warning of a quieter, more far-reaching danger: Extreme heat is devastating the health and livelihoods of tens of millions more.
If global greenhouse gas emissions continue at their current pace, they say, heat and humidity levels could become unbearable, especially for the poor.
It is already making them poorer and sicker. Like the Kolkata street vendor who squats on his haunches from fatigue and nausea. Like the woman who sells water to tourists in Delhi and passes out from heatstroke at least once each summer. Like the women and men with fever and headaches who fill emergency rooms. Like the outdoor workers who become so weak or so sick that they routinely miss days of work, and their daily wages.
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. Its a major public health challenge.
Indeed, a recent analysis of climate trends in several of South Asias biggest cities found that if current warming trends continued, by the end of the century, wet bulb temperatures a measure of heat and humidity that can indicate the point when the body can no longer cool itself would be so high that people directly exposed for six hours or more would not survive.
In many places, heat only magnifies the more thorny urban problems, including a shortage of basic services, like electricity and water. For the countrys National Disaster Management Agency, alarm bells rang after a heat wave struck the normally hot city of Ahmedabad, in western India, in May, 2010, and temperatures soared to 118 degrees Fahrenheit, or 48 Celsius: It resulted in a 43 percent increase in mortality, compared to the same period in previous years, a study by public health researchers found.
Since then, in some places, local governments, aided by the Natural Resources Defense Council, an advocacy group, have put in place simple measures. In Ahmedabad, for instance, city-funded vans distribute free water during the hottest months. In the eastern coastal city of Bhubaneswar, parks are kept open in afternoons so outdoor workers can sit in the shade. Occasionally, elected officials post heat safety tips on social media. Some cities that had felled trees for construction projects are busy trying to plant new ones.
The science is unequivocally worrying. Across the region, a recent World Bank report concluded, rising temperatures could diminish the living standards of 800 million people.
Worldwide, among the 100 most populous cities where summer highs are expected to reach at least 95 degrees Fahrenheit by 2050, according to estimates by the Urban Climate Change Research Network, 24 are in India.
Rohit Magotra, deputy director of Integrated Research for Action and Development, is trying to help the capital, Delhi, develop a plan to respond to the new danger. The first step is to quantify its human toll.
Heat goes unreported and underreported. They take it for granted, Mr. Magotra said. Its a silent killer.