Standing behind the counter of his grocery store in Noida, on the outskirts of New Delhi, Deepak Kumar laments the searing temperatures that have enveloped much of India this month.  Wearing a modest vest and thin cotton towel around his waist, he gestures to the rickety fan whirring slowly overhead as his only protection against the oppressive heat. “I sprinkle water on the hot floor to sleep. If I’m lucky with the water supply I can lie on a wet sheet,” said Mr. Kumar, 30, adding the problem gets worse every year.

Northern India is in the midst of a long and deadly heatwave that began more than two weeks ago, an occurrence that is predicted to become more severe due to climate change. Six of the hottest years ever recorded in India have taken place this century.  “It’s historically unusual, but for the past decade, we have had the highest temperature every year. This is becoming the new normal,” said Tarun Gopalakrishnan, deputy program manager for climate at the Centre For Science and Environment, an Indian think-tank.

Economists believe these more frequent and prolonged heatwaves, which take a significant economic toll in terms of heat-related deaths and lost labor productivity, will be one of the most visible near-term results of global warming. Big cities with dense populations in already hot climates, such as India’s sprawling capital, will be among the worst affected.

The temperature in New Delhi touched a record 48C (118 F)on June 10 as the city of more than 21m people sizzled. In Churu, in arid Rajasthan province on the edge of the Thar desert, it has exceeded 50C twice this month, just missing the record 51C hit during a heatwave two years ago.

Kuldeep Srivastava, a climate scientist at the Indian Meteorological Department, said: “There’s been a rise of almost 1-2C across the country’s north-west over the past 50 years.”

Rising heat poses a grave challenge to India’s fast-growing population of 1.3bn people. A recent Stanford University study argued that global warming had already slowed India ‘s economy by 31 percent from where it would have been otherwise and that this trend would continue. “The more countries warm up, the more drag there is going to be on their development,” wrote Noah Diffenbaugh, lead author of the study.