A billion people could be living with potentially lethal levels of heat stress if global warming were to reach 2C, research has found.

Heat stress – a combination of dangerous heat and humidity – currently affects 68 million people globally.

New modelling from a consortium of academics and the Met Office showed that under a 2C scenario, the number of people living in these conditions could rise 15-fold.

Heat stress is defined as a wet bulb globe temperature (WBGT) – a measurement taking into account temperature, humidity, wind speed and solar radiation – of above 32C.

It can induce heat exhaustion, with symptoms including heavy sweating and a rapid pulse, which can in turn put a strain on the heart and other organs.

The elderly, those with pre-existing health conditions and those with physical, outdoor jobs are at the greatest risk.

According to analysis, the earth was on course for 2.7C of warming under countries’ carbon emissions reduction pledges going into the Cop26 climate negotiations.

US climate envoy John Kerry revealed on Thursday that if the pledges made so far during the summit are kept, it would put humanity on course for 1.8C, the International Energy Agency has said.

The Met Office warned that in a future where runaway global warming reaches 4C, half of the world’s population would be living with heat stress.

The heat stress maps are part of research projecting the future impacts of different consequences of climate change under 2C and at 4C, and also look at river flooding, wildfire risk, drought and food insecurity.

It was conducted by an international team of scientists in the EU-funded Helix project, and led by the University of Exeter

The Met Office analysed where the most severe projected impacts overlap on behalf of the UK Government.

Dr Andy Hartley, climate impacts lead at the Met Office, said: “Currently, the (heat stress) metric is met in several locations, such as parts of India, but our analysis shows that with a rise of 4C, extreme heat risk could affect people in large swathes of most of the world’s continents.”

Prof Richard Betts, of the University of Exeter and Met Office – who led the Helix project, said “This new combined analysis shows the urgency of limiting global warming to well below 2C.

“The higher the level of warming, the more severe and widespread the risks to people’s lives, but it is still possible to avoid these higher risks if we act now.”

Dr Andy Wiltshire, head earth system and mitigation science at the Met Office, said: “Of course, severe climate change will drive many impacts, and our maps show that some regions will be affected by multiple factors.

“Perhaps unsurprisingly, parts of the tropics are most affected with countries like Brazil and Ethiopia potentially facing impacts from four of the hazards.

“Rapid emission reductions are required if we are to avoid worst consequences of unmitigated climate change.”