By Henry Bodkin, science correspondent
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, 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 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.
Sea levels could rise by around 30cm to 60cm by 2100 even if greenhouse gases are rapidly cut and global warming is kept to well below 2C above pre-industrial levels, but around 60-110 cm if emissions continue to increase, the analysis found.
Meanwhile annual coastal flood damages are projected to increase 100 to 1,000 times by 2100, and some island nations are "likely to become uninhabitable".
Hans-Otto Portner, another IPCC expert, said: “There are large uncertainties about tipping points that may be ahead of us, but for some systems, especially biological evidence in the oceans, we have already evidence that the tipping point has been passed.”
The warnings come as the UK government announced international coalition to push for at least 30 per cent of oceans to be in protected areas by 2030.
Ministers say the move helps sensitive species such as seahorses, turtles and corals to thrive, and can fight climate change by protecting key habitats for storing carbon such as mangrove forests and seagrass meadows.
Historically the Antarctic Ocean has an ice-free September only once every 100 years or so, however if global temperatures rise to two degrees above pre-industrial levels this would become as frequent as every three years, the panel said.
The commits signatories to adopting policies intended to keep warming to within 1.5 degrees.
However, Donald Trump has since withdrawn the US from the agreement.
In one of her last acts as Prime Minister, Theresa May set a legally-binding target to cut greenhouse gasses to net-zero by 2050 in June.
Last year a separate IPCC report called for 45 per cent reductions in carbon emissions by 2030.
"If we reduce emissions sharply, consequences for people and their livelihoods will still be challenging, but potentially more manageable for those who are most vulnerable," said Hoesung Lee, chair of the body, on Wednesday.”
Professor Peter Wadhams, professor of ocean physics at the University of Cambridge, said the report had failed to mention the "very serious threat" of methane rising from the seabed of the Arctic continental shelf as its permafrost thaws, potentially contributing large amounts of extra greenhouse gas.
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Related to SDG 13: Climate action
