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 world leaders gather in Belém, 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.
Watch: More leaders need to 'tell it as it is' om climate, Taoiseach tells COP30
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 Niño 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 Niño/La Niña 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."
He said it could push ecosystems past irreversible tipping points, expose billions of people to un-livable conditions, and amplify threats to peace and security.
"Every fraction of a degree means more hunger, displacement, and loss – especially for those least responsible. This is moral failure – and deadly negligence," he said.
Watch: Guterres says political courage is needed to transition to clean energy
He said the United Nations will not give up on the 1.5 degrees goal and that we have never been better equipped to fight back.
He spoke about the clean energy revolution with solar and wind, now the cheapest sources of power, and the fastest growing sources of electricity in history.
In 2024, investors poured 2 trillion US dollars into clean energy – 800 billion more than fossil fuels.
"Clean energy is winning on price, performance, and potential – offering the solutions to transform our economies and protect our populations. What's still missing is political courage", he said.
"Fossil fuels still command vast subsidies – taxpayers’ money. Too many corporations are making record profits from climate devastation – with billions spent on lobbying, deceiving the public and obstructing progress. Too many leaders remain captive to these entrenched interests. Too many countries are starved of the resources to adapt – and locked out of the clean energy transition," he added.
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 that ocean heat 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.
The WMO highlighted too that 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.
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."
Lula warns world leaders of 'extremist forces' lying about climate
President Luiz Inacio Lula da Silva of COP30 host Brazil said that "extremist forces" were condemning future generations to life on a planet forever altered by global warming.
Mr Lula lashed out at "extremist forces (that) fabricate fake news ... to obtain electoral gains and imprison future generations," as he warned that the window to prevent calamitous climate change was "closing rapidly".
Mr Lula pointed to a recent UN report that found Earth will likely be 2.5C warmer by 2100 from pre-industrial levels.
This would claim an estimated 250,000 lives per year and shrink global GDP by almost a third, he told dozens of leaders gathered in Belem.
"Now is the moment ... to face reality and decide if we will have the courage and the necessary determination to transform things," the president urged.
But he pointed to a tendency of "selfish immediate interests" prevailing over the long-term common good.
Global climate efforts have been tarnished by "insecurity and mutual mistrust," said Mr Lula, who has been involved in a heated tariff spat with counterpart Donald Trump of the United States, which was absent from the high-level climate talks.
Brazil president launches forest fund at climate summit
Mr Lula launched a fund today to protect the world's forests, key absorbers of planet-warming carbon.
In what Mr Lula dubbed "one of the main tangible outcomes" expected from the gathering, the so-called Tropical Forest Forever Facility is meant to gather investments of $125bn from governments and private investors in the long term, with startup funding of $10bn that has not yet been received.
"When forest destruction reaches irreversible points, its effects will be felt across the world. Forests are worth more standing than cut down. They should be part of the GDP of our countries," said Mr Lula.
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Additional reporting by George Lee
