Climate change is now irreversible, thanks to ocean warming crossing a “tipping point”, UN experts have warned.

A new report predicts that, even with significant emission cuts, sea levels will rise by the end of the century, with serious coastal flooding becoming hundreds of times more frequent.

The planet has warmed to 1C above pre-industrial temperatures, and around 90 per cent of that excess heat has been absorbed by the oceans, the Intergovernmental Panel on Climate Change said.

It means rapidly melting ice in Antarctica and Greenland is now pushing up sea levels by 3.6mm a year, at twice the rate of the Twentieth Century.

Despite commitments by the UK, French and other governments to achieve net-zero carbon emissions in coming decades, the analysis predicts that there is too much heat in the oceans to prevent disruption for hundreds of millions of people.

Unveiling the latest report in Monaco on Wednesday, panel-member Valerie Masson-Delmotte, said: “Climate change is already irreversible due to the heat uptake in the ocean.

“We can’t go back, whatever we do with our emissions.”

According to the new forecasts, approximately 70 per cent of the world’s permafrost will thaw if emissions continue to rise. This in turn could free up “tens to hundreds of billions of tonnes” of CO2 and methane into the atmosphere, further heating the planet.