Ten million people are “likely to die” due to extreme temperatures if world leaders fail to agree significant cuts in greenhouse gas emissions by 2030, a report has warned.

Agricultural output could also drop by 30% by 2050 – even as the amount of food needed by growing populations is predicted to rise by 50%, according to international affairs think tank Chatham House.

The report produced for governments ahead of COP26, the UN climate meeting in Glasgow this November, said severe impacts of climate change will be “locked in” from 2040 unless greenhouse gas emissions “drastically” decline before 2030.

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Corn crops are especially likely to suffer, with the think tank predicting at least a 10% drop in yields in the US, China, Brazil and Argentina, where most crops are grown.

More than 400m people would be “unable to work outside” by the 2030s, with 10m deaths predicted due to “heat stress”, the report said.

By 2040, researchers said almost 700m people each year would probably be exposed to severe droughts lasting at least six months – and by 2050, more than 70% of people in every region of the world would probably experience heatwaves.

The amount of flooding would surge by the turn of the next century, with the study’s authors warning nearly 200m people worldwide would probably be living below the 100-year flood level – the level at which water begins to overflow into the surrounding area.

Almost 60m people would likely be affected by river flooding due to the rise in the relative sea level, the report said.

The authors said the probability of flood events that currently happen once every 100 years increases with just a one-metre rise in the relative sea level, jumping by 40 times for Shanghai, 200 times for New York and 1000 times for Kolkata.

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They said the current pace of global decarbonisation efforts mean the world is on track for at least 2.7C in warming by the end of the century – well above the 1.5C target.

The report noted that new proposals by some governments to further cut emissions fall far short of what is required to meet the target, while several major economies are yet to commit to any further emission reduction goals.

At COP21 in Paris in 2015, countries agreed to try to limit global warming to 2C above pre-industrial levels to curb the climate crisis.

Dr Daniel Quiggin, a senior research fellow at Chatham House who co-authored the report, said: “There remains a real opportunity yet a closing window for greatly increased ambition from all governments to prevent the most catastrophic impacts of climate change.”

He added that there is also “the increasing possibility that climate-related events trigger a sequence of connected incidents across regions and sectors which cause trade disruption, political instability, increased migration, an increase in infectious diseases or even armed conflict”.

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Jamie Peters, director of campaigning at Friends of the Earth, called the report “horrifying” but said he does not think it is possible to be “too late” to respond to climate change.

“Every point of a degree is a question of lives,” he told Sky News.

He urged the UK government to “get its act together” and drop its support for all fossil fuel projects – like airport expansions, coal mines and gas projects.

He said doing this would give Britain the legitimacy needed to demand action from other countries.

The speed of climate change has shocked many people in the past,” he said. “The science has been clear and the projections get more and more stark.”

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