Hans-Otto Pörtner, co-chair of the IPCC’s Working Group II, said: “The scientific evidence is unequivocal: climate change is a threat to human wellbeing and the health of the planet.

“Any further delay in concerted global action will miss a brief and rapidly closing window to secure a liveable future.”

John Kerry, US, special presidential envoy for climate, said: “We have seen the increase in climate-fueled extreme events, and the damage that is left behind—lives lost and livelihoods ruined.

“The question at this point is not whether we can altogether avoid the crisis—it is whether we can avoid the worst consequences.”

‘Considerable changes in our lifetime’

Professor Albert Klein Tank, director of the Met Office’s Hadley Centre, said: “Preventing debilitating impacts on society from increasing climate change is no longer a choice – that option closed several decades ago.

“Today’s report says it is vital to adapt to the increasing climate change we are already seeing and what we know we will see in future.

“But of course lowering greenhouse gas emissions will help to avoid the most extreme climate change impacts.”

Cop26 president Alok Sharma said: “It is happening much faster, and the impacts are more extreme than previously thought.

“We will witness considerable changes in our lifetime and without ambitious action, millions across the planet could no longer have anywhere to call home.”

Scientists warned that while developing countries were particularly vulnerable to the impacts of climate change, the UK would also experience effects including higher food prices, growing river flooding and coastal erosion.

Dr Peter Alexander, lead author of the report’s European chapter, said: “We import close to half the food that we consume within the UK, and if the rest of the world’s agriculture is being impacted by climate change, then we’re going to effectively import those impacts to the UK, largely through potentially higher food prices.”

More funds need to be directed to adapting to the effects of climate change, including disaster warnings, restoring nature, water efficiency, coastal defences and more resilient agriculture, the report said.

But in some cases efforts to adapt can make the problem worse. Measures such as planting trees in the wrong places or burning wood pellets for energy “can compound climate-related risks to biodiversity, water and food security, and livelihoods,” the report warns.

There is also “emerging evidence” that young people across Europe have anxiety about climate change, while people displaced because of flooding in 2013-2014 floods in England were more likely to experience PTSD, depression and anxiety, the report says.