Garment worker Raj Pal often sleeps on the roof of his one-room home near India’s capital to try to escape the sweltering heat, but even so headaches and exhaustion mean he sometimes misses work and can lose as much as a quarter of his £200-a-month pay.

Researchers said relying on the resilience of garment workers to endure the withering effects of climate change was likely to undermine India’s drive to become a global force in garment manufacturing and boost the sector’s exports from the current $40 billion to $100 billion by 2030.

India’s garment industry employs around 45 million people and accounts for about 12 per cent of its exports.

“It feels like my hands will fall off from the shoulder,” Pal said, describing how he feels at the end of a typical 15-hour working day.

New York University’s Stern Center for Business and Human Rights said in a report on India’s garment sector last month that extreme heat led to greater absenteeism, lower productivity, more product defects and more frequent disruptions caused by power failures and overheating equipment.

Managers estimated productivity fell by between 3 per cent to 10 per cent during peak summer months, while workers said they suffered health problems and wage losses, the report said.

“The key lesson is that heat can no longer be viewed solely as a worker safety issue,” said Lucy Siers, co-author of the report. “It is increasingly an operational, productivity and supply chain resilience issue.”