Heat is accumulating in Earth’s systems at an accelerating rate, the UN’s weather agency has reported as the Cop31 climate change summit begins in Turkey, with 2026 on track to be one of the four warmest years on record.

The imbalance between incoming energy from the sun and energy leaving Earth reached its highest level since monitoring began, the World Meteorological Organization (WMO) said in its State of the Global Climate update.

That imbalance and the accumulation of heat will supercharge extreme weather events such as heatwaves, droughts and tropical cyclones.

Around the world, the average surface temperature for January to September 2026 was about 1.47C above the preindustrial average, the agency said. Sea surface temperatures hit monthly records and sea level was the highest since records began. The ocean absorbs 90% of the excess heat trapped by greenhouse gases and 2026 is on track to be a 10th successive year of record ocean heat.

A centre for people experiencing respiratory difficulties in Palangkaraya, Indonesia. More than 11,000 people have been treated during a months-long wildfire crisis. Photograph: REINA/AFP/Getty Images

“We have entered a new age of climate extremes,” said António Guterres, the UN secretary general. “A supersized El Niño is colliding with a planet already superheated by manmade climate change. Climate records keep falling. The human costs keep rising. And those least responsible are suffering first and worst.”

Diplomats and world leaders are meeting on Monday in the Turkish resort city of Antalya for the 31st conference of the parties (Cop) to the UN framework convention on climate change. In 1992, when the convention was signed, the atmospheric concentration of carbon dioxide, the primary greenhouse gas, was 356.42 parts per million (ppm). In 2025 it was 426.8 ppm, the WMO said. Overall, since 1750, the onset of the Industrial Revolution, the concentration has increased 53%.

The WMO reported that ocean heat content estimates indicate Earth’s energy imbalance rose at a rate of 0.3W per sq metre each decade for the period 2001–2025, compared with 0.13W per sq metre between 1960 and 2025.

Accordingly, 2026 is on track to be one of the four warmest years on record globally, making 2023 to 2026 the four warmest years since records began.

The Cop31 climate summit begins in Antalya, Turkey, on Monday. Photograph: Murad Sezer/Reuters

The year started with La Niña conditions in the Pacific, which typically act as a brake on global temperatures, lowering the average by about 0.1-0.2C. A brewing El Niño, a phenomenon that warms global temperatures, and whose latest iteration is forecast to be stronger than any to have taken place in the past 1,000 years, makes it likely that the final mean temperature for 2026 will be higher than 1.47C above the pre-industrial average.

Heat in the upper 2,000 metres (6,500ft) of the ocean in 2025 was the highest in the observed record and was accelerating, the WMO said. “This warming is projected to continue, representing a change that is irreversible on centennial to millennial timescales,” according to the report.

At the poles, Antarctic sea ice reached its third-lowest annual maximum ever in 2026, while the Arctic maximum was the lowest or second lowest. Elsewhere in the cryosphere, glaciers lost more than 400 gigatonnes of mass. It was the fourth consecutive year in which all 19 glacierised regions around the world experienced mass loss, the WMO said.

Bill McGuire, a professor emeritus of geophysical and climate hazards at University College London, said there were “no surprises” from the report, “to the extent that every measure reported, whether it be global temperature, sea level rise or sea ice extent, points to the fact that we are in deep shit”.

He said: “Of most concern is the growing imbalance between the incoming energy from the sun and that leaving the planet. Increasing greenhouse gas concentrations in the atmosphere mean that while the heat coming in stays the same, that going out is steadily decreasing as our world hangs on to more and more of it.

“It is this growing imbalance – rather than just emissions – that most accurately tracks global heating and how quickly our planet will continue to heat up in the decades to come. This is because natural feedbacks are now coming into play that are driving up the temperature more rapidly than 20 years ago.

“The latest research suggests we will cross the 1.5C limit permanently in 2028, and with the planet now heating at an extraordinary rate of 0.4C a decade, we can expect to smash through 2C in the late 2030s.

“The widely publicised idea that we are still on track for 2.6-2.8C by the end of the century now seems wildly optimistic, if not downright impossible.”