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New York
The combined effects of rising heat and humidity will affect India's northeast the most in the world close to the end of of the century, a global study says.
Although humidity can greatly magnify the effects of heat, most climate projections tend to leave out this major factor that could worsen things.
The new study, published in the journal Environmental Research Letters, projects that in coming decades the effects of high humidity in many areas will dramatically increase. While hundreds of millions of people would suffer worldwide, the hardest-hit area in terms of human impact, will probably be densely populated northeastern India, the researchers said.
"The conditions we're talking about basically never occur now people in most places have never experienced them,"said lead author Ethan Coffel of Columbia University in New York.
"But they're projected to occur close to the end of the century,"Coffel said. Using global climate models, the researchers mapped current and projected future"wet bulb"temperatures, which reflect the combined effects of heat and humidity.
The measurement is made by draping a water-saturated cloth over the bulb of a conventional thermometer.
The study found that by the 2070s, high wet-bulb readings that now occur maybe only once a year could prevail 100 to 250 days of the year in some parts of the tropics.
Lab experiments have shown wet-bulb readings of 32 degrees Celsius are the threshold beyond which many people would have trouble carrying out normal activities outside.
"Lots of people would crumble well before you reach wet-bulb temperatures of 32 C, or anything close,"said coauthor Radley Horton, a climate scientist at Columbia University's Lamont-Doherty Earth Observatory.
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