United Nations Secretary-General Antonio Guterres has issued his latest climate SOS, calling on countries to “Save Our Seas” as he warned of a crisis of an “unimaginable scale” caused by greenhouse gases and rising sea levels.

Speaking at a gathering of Pacific Island regional leaders on Tuesday in Tonga’s capital Nuku’alofa, he warned there was “no lifeboat to take us back to safety”.

“This is a crazy situation: Rising seas are a crisis entirely of humanity’s making. A crisis that will soon swell to an almost unimaginable scale,” he said. “The reason is clear: Greenhouse gases – overwhelmingly generated by burning fossil fuels – are cooking our planet. And the sea is taking the heat – literally.”

Nuku’alofa is hosting more than 1,000 international delegates for the Pacific Islands Forum Leaders Meeting until August 30. Climate change and its impact on the Pacific’s low-lying communities is high on the agenda at the gathering of regional officials, who lead some of the world’s most imperilled countries.

Guterres, who last attended the Leaders Meeting in 2019, warned that with about 90 percent of people living within 5km (3 miles) of the coast, and an average elevation of just one to 1-2 metres (3.2-6.5 ft) above sea level, the “Pacific islands are uniquely exposed”.

He is also expected to visit Samoa while he is in the Pacific.

“Without drastic cuts to emissions, the Pacific Islands can expect at least 15 centimetres [6 inches] of additional sea level rise by mid-century, and more than 30 days per year of coastal flooding in some places,” he said. “But if we save the Pacific, we also save ourselves. The world must act and answer the SOS before it is too late.”

Among the Pacific Islands’ most ambitious climate change mitigation efforts is the Pacific Resilience Facility. The “Pacific-owned and led” financial institution, which will support local communities to become more resilient to climate change, is scheduled to start operations in 2025 but is facing a severe shortfall in funding from international donors.

Guterres repeated his longstanding appeal to “the biggest emitters”, the Group of 20 (G20) nations, to financially support the world’s most climate-vulnerable countries.

“We need a surge in funds to deal with surging seas,” he said.