The emissions from burning oil and gas produced by the world’s leading fossil fuel companies could cause millions of excess heat deaths before the end of the century, according to a new analysis.

The study from Global Witness found that the combined emissions from fossil fuels produced by Shell, BP, TotalEnergies, ExxonMobil and Chevron up to 2050 could result in 11.5 million excess deaths from heat by 2100.

The findings represent the first attempt to quantify heat deaths resulting from planned oil production by big oil and add weight to calls to drastically reduce fossil fuel extraction.

Sarah Biermann Becker, senior investigator at Global Witness, said: “Every 0.1C of warming will be lethal. Unless the supermajors change course quickly, the death toll will be comparable to some of history’s most brutal wars. We cannot leave it up to them. Governments need to step in, mitigate the impact of extreme heat and urgently ramp up the transition away from fossil fuels.”

The report used the mortality cost of carbon model devised by academics at Columbia University and used by Oxfam – among others. It calculates that in a high emissions scenario – which is predicted to happen to the climate if no further concerted action is taken to rapidly reduce warming – there will be 226 excess heat deaths worldwide for every million tonnes of carbon released.

It then used data from leading analysts Rystad Energy to calculate projected emissions from fossil fuels produced by the oil firms. It calculated that together they would add 51bn tonnes of carbon dioxide emissions to the atmosphere by 2050. Based on the high emissions scenario that would result in 11.5 million excess heat deaths by the end of the century.

The analysis found that if the world managed a lower emissions scenario, reaching net zero globally by 2050, excess deaths associated with the companies’ production would come to about 5.5 million people.

Intense and deadly heatwaves have hit almost every continent over the past few years, sparking wildfires and causing hundreds of thousands of excess deaths. In Europe, searing heat killed more than 60,000 people in 2022 and heat-related deaths rose by 95% in the US between 2010 and 2022.

Heat often hits the poorest and most vulnerable members of each society hardest, with the homeless, those who work outside and the elderly most at risk.

Shouro Dasgupta, an environmental economist at the Euro-Mediterranean Center on Climate Change, said action needed to be taken to protect the most vulnerable.

“We’re already seeing the impacts of heat stress on workers around the world, particularly on people in outdoor or heavy-duty industries such as agriculture and construction.

“This will likely get much worse as the planet continues to heat up. We need labour protection policies that are tailored to local needs rather than a one-size-fits-all approach. This isn’t just a moral question – it’s also in the economic interests of employers to provide adequate protection for their workers.”

Experts point out that heat deaths will be just one result of a failure to rapidly transition away from fossil fuels alongside other disasters such as food shortages, flooding and political and economic turmoil.

The big oil corporations continue to invest billions in new oil and gas reserves and BP and Shell have recently weakened their climate pledges.

In response to Wednesday’s analysis, TotalEnergies said it was continuing to invest in new oil projects to offset the “natural decline” in existing production in order to meet expanding global demand.

Along with Shell and BP, it said it was investing in renewable and low-carbon energy to support a just transition to a low-carbon energy system.

BP added that since it had not set out its oil and gas production beyond 2030, predictions based on its plans to 2050 were invalid.

BP and Shell said they had made progress in reducing emissions from their operations. Shell questioned some of the methodology used in the analysis.

A spokesperson for Shell added: “The pace of transition depends on action in many areas, including government policy, changing customer demand and investment in low-carbon energy. Our aim is to play our part in a balanced energy transition, where the world achieves net zero emissions without compromising on delivery of secure and affordable energy, which has improved so many lives, and which people will continue to need today and for many years to come.”

Exxon and Chevron did not respond to requests for comment.