For years the most remote continent on Earth had seemed largely immune to climate change, with satellites showing that sea ice extent grew despite global warming. But now scientists are growing concerned after evidence shows that Antarctica has suffered sea ice lows four years in a row.

Between 1978 and 2015 Antarctic ice extent was seen to grow at a steady rate, despite the planet warming and levels of greenhouse gases increasing. One reason is that winds around the continent appear to have insulated it from warmer air.

However, the World Meteorological Organisation (WMO), the Geneva-based UN agency, said in a report on Wednesday that the trend in ice extent appeared to be reversing.

Celeste Saulo, the secretary-general of the WMO, said: “The frozen parts of Earth’s surface, known as the cryosphere, are melting at an alarming rate: glaciers continue to retreat, and Antarctic sea ice reached its second-lowest extent ever recorded.”

While East Antarctica has experienced a growth in sea ice in the past, the west of the continent is more vulnerable. One glacier in the west, Thwaites, is dubbed the “doomsday glacier” because its loss could cause the collapse of other glaciers, causing 3.3 metres of global sea-level rise and threatening low-lying cities — including London.

Before 2022, Antarctica’s minimum sea ice extent — the lowest it gets during the southern hemisphere summer — had never been lower than 2 million square kilometres. But it has now been below the threshold for four years running. 2025 tied with 2022 for joint second-lowest, at 1.98 million square kilometres.

John Kennedy, the scientific coordinator of the report, said there had been warming below the surface in the Southern Ocean. The sea ice lows in recent years appeared to be related to some of that heat coming to the surface, he said.

Scientists said it was too early to say if Antarctica had flipped into a new pattern.

Karina von Schuckmann, an oceanographer at Mercator Ocean International, a French research institute, said: “There are many studies which are coming out, and there is no clear consensus yet. There are studies which have shown the impact of variability, the impact of changing winds, there are discussions about the warming on the ocean side.”

Kennedy said the changes mattered for people on the other side of the world because of their impact on sea level. “What happens in the poles doesn’t necessarily stay at the poles,” he said.

The sparse sea ice in Antarctica over the past two years may also have “played a role” in the record-breaking global temperatures seen in 2024 and 2023, the WMO said. However, the main reason for the record heat was climate change, Kennedy said. The past ten years have all been in the top ten warmest on record.

The agency’s report found levels of carbon dioxide in the atmosphere are now at the highest they have been for 800,000 years, as the emissions produced by humanity have kept climbing higher.

The result is that each of the past eight years set a new global record for heat in the oceans, which are absorbing much of our emissions. Sea levels are rising too, at twice the rate in the past ten years as they did between 1993 and 2002. Last year, the global average sea level hit its highest point since satellite records began in 1993.

António Guterres, the UN secretary-general, said the new data showed “our planet is issuing more distress signals”.

The UK and nearly 200 other countries will head to a Brazilian port city in the Amazon rainforest in November for the Cop30 international climate talks, in an attempt to curb global emissions.

“This report shows that limiting long-term global temperature rise to 1.5C is still possible,” said Guterres. “Leaders must step up to make it happen — seizing the benefits of cheap, clean renewables for their people and economies — with new national climate plans.”