United Nations Secretary-General Antonio Guterres warned today that sea levels will rise significantly even if global warming is “miraculously” limited to 1.5 degrees Celsius — and said Earth is more likely on a path to warming that amounts to “a death sentence” for countries vulnerable to that rise.

Every fraction of a degree counts, since sea level rise could double if temperatures rise by 2C, and increase exponentially with further temperature increases, the UN chief said. He spoke at the opening of a UN Security Council meeting on sea level rise, which was hearing from 75 countries, and said the council has a critical role in building support for actions to fight climate change.

Under any scenario, countries like Bangladesh, China, India and the Netherlands are all at risk, and large cities on every continent will face serious impacts, including Cairo, Lagos, Maputo, Bangkok, Dhaka, Jakarta, Mumbai, Shanghai, Copenhagen, London, Los Angeles, New York, Buenos Aires and Santiago, he added.

The World Meteorological Organisation released figures Tuesday, cited by Guterres, that say global mean sea level will rise by about 2-3 metres over the next 2000 years if warming is limited to 1.5C. With a 2C increase, seas could rise up to 6m, and with a 5C increase, seas could rise up to 22m, according to the WMO.

 “Our world is hurtling past the 1.5C warming limit that a liveable future requires, and with present policies, is careening towards 2.8C — a death sentence for vulnerable countries,” Guterres said.

Guterres said the danger is especially acute for nearly 900 million people who live in coastal zones at low elevations, or one out of every 10 people worldwide.

The consequences are unthinkable, Guterres said: Low-lying communities and entire countries could disappear, the world would witness a mass exodus of entire populations on a Biblical scale and competition would become ever fiercer for fresh water, land and other resources.

Waves crash into reinforced seawalls in Shishmaref, Alaska, in October last year. Rising sea levels, flooding and increased erosion have led residents of this island community to vote twice to relocate. Photo / AP

Guterres has been trying to call the world’s attention to the dangers posed by climate change, to spur action.

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In October, he warned that the world is in “a life-or-death struggle” for survival as “climate chaos gallops ahead” and accused the world’s 20 wealthiest countries of failing to do enough to stop the planet from overheating.

In November, he said the planet is heading toward irreversible “climate chaos” and urged global leaders to put the world back on track to cut emissions, keep promises on climate financing and help developing countries speed their transition to renewable energy.

The landmark Paris agreement adopted in 2015 to address climate change called for global temperatures to rise a maximum of 2C by the end of the century compared to pre-industrial times, and as close as possible to 1.5C.

Guterres said the world must address the climate crisis as the root cause of rising seas, and the Security Council has a critical role to play in building the political will required.