The percentage of the world’s population experiencing extreme heat could double by 2050 over the 2010 benchmark because of continued use of fossil fuels, with India becoming one of the biggest sufferers, a research carried out by scientists at Oxford University has found.

The report has been published in the journal Nature Sustainability, a leading global publication in environmental studies, and is described as a “wake-up call” by one of the authors. The report said that if global temperatures rise by 2°C, projected to happen in about 25 years based on continuing use of fossil fuels, around 3.79 billion individuals are likely to face extreme heat. In 2010, that number had been projected to be 1.54 billion in 2050.

Extreme heat is a period of abnormally hot weather, often defined by temperatures above 32°C for several days.

“India, Nigeria, Indonesia, Bangladesh, Pakistan and the Philippines are projected to have the largest populations living under extreme heat, living under more than 3,000 cooling degree days,” said lead author Jesus Lizana.

Cooling degree days measure the energy needed to keep indoor environments at safe temperatures. “A threshold of 3,000+ CDD indicates prolonged, intense annual heat,” the report said.

“Our study shows most of the changes in cooling and heating demand occur before reaching the 1.5°C threshold (and) many homes may need air conditioning to be installed in the next five years, but temperatures will continue to rise long after that if we hit 2°C of global warming,” Lizana said.

“Our findings should be a wake-up call,” says Radhika Khosla, a professor and another author of the study, adding: “Overshooting 1.5°C of warming will have an unprecedented impact on everything from education and health to migration and farming. Net-zero sustainable development remains the only established path to reversing this trend for ever hotter days. It is imperative that politicians regain the initiative towards it.”

Despite the Paris climate agreement in 2015, mandated to keep the global temperature rise within 1.5°C, at most 2°C, compared to the pre-industrial-era benchmark, the global temperature has already risen tantalisingly close to 1.5°C. The report points out that the percentage of the “world’s population living in regions defined as extremely cool could halve from 14 per cent to 7 per cent”, as fewer places will be “extremely cool”.

The report highlights that India is among the countries projected to experience the largest population exposure to extreme heat conditions under global warming scenarios. “These findings emphasise the growing vulnerability of India’s population to extreme heat and the need for targeted adaptation and mitigation strategies to address the impacts of rising temperatures,” the report said.

Anjal Prakash, a climate expert and professor at the Indian School of Business, Hyderabad, said: “The Oxford study highlights a critical climate tipping point: if fossil fuel dependence is not reduced swiftly, extreme heat — which is already fatal — could threaten twice the current global population by 2050, particularly in vulnerable nations such as India….

“These areas, characterised by high population density and inadequate infrastructure, face elevated threats to health, agriculture, and economies, increasing inequality.”

“India, especially its northern part, reflects intensifying trends where heat waves worsen air pollution issues. Prompt action is crucial, requiring accelerated adoption of renewables, green finance, and equitable policies in line with climate COP commitments. Any delay could lead to irreversible consequences,” said Prakash, a scientist and a lead author of the United Nations Special Report on Climate Change and Cities, which will be part of the next UN overall assessment report on climate change.

The Central African Republic, Nigeria, South Sudan, Laos and Brazil will likely see the greatest increase in cooling needs per person, while Canada, the Russian Federation, Finland, Sweden and Norway will witness the greatest decrease in heating needs per person as the weather will get rapidly warmer.