Warning over 1.5C climate goal as 2025 set to be among hottest years on record

This year is on track to be the second or third warmest globally as an “unprecedented streak” of high temperatures continues, UN scientists have warned.

Global average surface temperatures in January to August 2025 were 1.42C above pre-industrial levels, the World Meteorological Organisation (WMO) said, a slight drop from the record highs of 1.55C in 2024.

As leaders gather in Belem, Brazil, for the latest round of UN climate talks, the WMO said it was “virtually impossible” to curb global warming to the agreed limit of 1.5C above pre-industrial levels in the next few years without temporarily overshooting the target.

But it is “still entirely possible and essential” to bring temperatures down to the 1.5C goal by the end of the century, WMO secretary-general Celeste Saulo said.

The latest UN talks come in the wake of a year in which people around the world have been battered by climate and weather extremes from damaging rainfall and floods to severe heat and wildfire – but as politicians in a number of countries seek to row back on action to combat the worsening situation.

This year has been slightly cooler than last year as the El Nino climate phenomenon in the tropical Pacific, which boosted global temperatures in 2023 and 2024, shifted to neutral conditions at the start of 2025.

The El Nino/La Nina pattern influences the global climate in addition to the warming caused by humans burning fossil fuels and cutting down forests, which put heat-trapping greenhouse gases into the atmosphere, pushing up temperatures and sea levels and causing more extreme weather.

The WMO’s analysis finds that the past 11 years – from 2015, when countries signed up to the Paris Agreement to pursue efforts to limit global warming to 1.5C to avoid its worst impacts, to 2025 – are individually the 11 warmest on record.

The past three years have been the three warmest years in the record stretching back 176 years, the WMO said.

The UN’s meteorological agency also warned that concentrations of greenhouse gases, which reached record levels in 2024, continued to rise in 2025.

Ms Saulo said: “This 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.

“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.”

UN secretary-general Antonio Guterres warned: “Each year above 1.5C will hammer economies, deepen inequalities and inflict irreversible damage.

“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.”

In an update to its annual state of the climate report timed to coincide with the start of the UN Cop30 talks in Brazil, the WMO highlighted:

– Ocean heat content continued to rise in 2025 above the record levels seen in 2024, with impacts including damage to natural systems, intensifying storms, accelerating sea ice loss and sea level rises.

– Long term rates of sea level rise have doubled, and 2024 set a new record for annual global average sea levels, though it has dropped slightly since 2025 in what the experts said is likely temporary behaviour;

– Arctic sea ice was at its lowest levels on record for the time of year after the winter freeze, while Antarctic sea ice was the third lowest on record for its annual minimum and maximum extents;

– Concentrations of three key greenhouse gases in the atmosphere, carbon dioxide, methane and nitrous oxide, were at record highs in 2024 and measurements from individual locations suggest they will be even higher in 2025;

– The world has been hit by extreme weather events, including flooding in many countries in Africa and Asia, wildfires in Europe and North America, extreme heat throughout the world and deadly tropical cyclones in 2025, causing loss of life and massive economic and social upheaval.

In response to the report, Gareth Redmond-King, from the Energy and Climate Intelligence Unit think tank said: “Nations are gathering for the start of the Cop30 climate summit at the end of a year that has seen devastating hurricanes, wildfires and flooding across the world; here at home, we’ve seen the second worst harvest as a result of climate change.”

He said that news that 2025 was set to be the second or third hottest on record, alongside warnings that current pledges of climate action still put the world on track for dangerous levels of temperature rise “should focus leaders’ minds”.

“Net zero emissions is the only solution we have to halt climate change, to limit the worsening danger and rising costs which this represents, and bring the climate system back into balance,” he said.