A triple-whammy of hottest years ever recorded threatens “irreversible damage”, the UN has warned as the world’s nations prepare to meet at the Cop30 climate summit in Brazil.

This year is on course to be the second or third hottest ever, in records that stretch back 176 years, the UN World Meteorological Organization (WMO) said. It means 2023, 2024 and 2025 will be the three hottest on record, demonstrating that the world is now deep into the climate crisis.

The past 11 years, back to 2015, will also be the 11 warmest years on record.

The WMO said limiting global heating to the Paris agreement target of 1.5C above preindustrial levels was now virtually impossible, echoing the UN secretary-general, António Guterres, and the UN Environment Programme (Unep), who have both said in the past week that the target was now unachievable.

“The unprecedented streak of high temperatures, combined with last year’s record increase in greenhouse gas levels, makes it clear that it will be virtually impossible to limit global warming to 1.5C in the next few years without temporarily overshooting this target,” said Celeste Saulo, the WMO secretary-general.

“But the science is equally clear that it’s still entirely possible and essential to bring temperatures back down to 1.5C by the end of the century,” she said. That would require carbon dioxide to be sucked from the atmosphere, by growing new forests and using technology to remove and bury the CO2.

“Each year above 1.5C will hammer economies, deepen inequalities and inflict irreversible damage,” said Guterres. “We must act now, at great speed and scale, to make the overshoot as small, as short, and as safe as possible – and bring temperatures back below 1.5C before the end of the century.” Scientists worry that overshooting the target could trigger climate tipping points and cause catastrophic damage.

Despite the accelerating rollout of renewable energy and electric vehicles, the world’s nations are falling drastically short of the action needed to cut the carbon emissions from fossil fuels.

The WMO reported in October that the levels of CO2 in the atmosphere soared by a record amount in 2024 to hit a new high. Scientists are worried the natural land and ocean sinks that remove CO2 from the air are weakening as a result of global heating, which could form a vicious circle and drive temperatures up even faster.

A natural El Niño event in 2023 and 2024 supercharged global heating but the climate system has now moved into neutral/La Niña conditions in 2025, reducing global temperatures a little. The Unep report said the upcoming withdrawal of the US from the Paris agreement will increase global heating by 0.1C in the coming decades.

The WMO report said the hydrological year, up to October 2024, has seen the largest loss of glacier ice in records running back to 1950. The year saw 450bn tonnes of ice lost, pushing up sea levels.

Extreme weather is being made more intense and frequent by the climate crisis, meaning early warning systems are more vital than ever to protect lives. The WMO said the number of countries with multi-hazard early warning systems has more than doubled since 2015, from 56 to 119 in 2024. However, 40% of countries still lack the systems, the agency said, and urgent action was needed to meet the UN goal of universal coverage by 2027.