Carbon dioxide, methane and nitrous oxide all reached record concentrations in the atmosphere in 2025, the World Meteorological Organization said in its annual Greenhouse Gas Bulletin released October 27, two weeks before the COP31 climate summit opens in Antalya, Türkiye.
“Another year, another new record,” said Ko Barrett, the WMO’s deputy secretary-general. “Greenhouse gases are trapping an unprecedented amount of heat in the atmosphere,” she said. “The past 11 years have been the warmest on record and this trend is set to continue.”
The numbers
The bulletin put the globally averaged surface concentration of carbon dioxide at 426.8 parts per million in 2025, or 153% of the pre-industrial level of 1750. When the bulletin was first published in 2004, the annual average was 377.5 parts per million, so the 2025 figure is 49.3 parts per million higher. The WMO said the growth rate of carbon dioxide rose from 0.8 parts per million per year starting in the 1960s to 2.4 parts per million per year in the 2011 to 2020 decade, meaning it has tripled. The increase from 2024 to 2025 was 2.8 parts per million. Carbon dioxide accounts for about 81% of the increase in warming influence from long-lived greenhouse gases between 1990 and 2025, the WMO said. The figures draw on observations from 179 stations.
Methane reached 1,948 parts per billion, or 267% of its 1750 level. The WMO said methane accounts for about 16% of warming from long-lived greenhouse gases. About 35% of methane comes from natural sources and about 65% from human activities, according to the bulletin.
Nitrous oxide reached 339.1 parts per billion, 126% above its 1750 level.
The bulletin also noted that sulfur hexafluoride, a gas with an atmospheric lifetime of more than 1,000 years and a 100-year warming potential of about 24,300 times that of carbon dioxide, had a record increase in 2025. It also reported that hydrogen concentrations rose 5.3% between 2010 and 2024.
Why growth slowed in 2025
The 2.8 parts per million increase from 2024 to 2025 was more modest than the year before. Oksana Tarasova, a senior scientific officer at the WMO, said the slower growth “reflects recovery of the land carbon sinks,” after conditions in the previous year had “reduced the efficiency of the biosphere through more drought, drier vegetation and more wildfires.” She added, “However, a 2.8 ppm annual increase is still a substantial addition of carbon to the atmosphere from fossil fuel burning.”
Barrett said carbon dioxide “has a very long life-time and so will affect the global climate not just for years but for decades and even centuries.”
Share of warming by gas
The WMO bulletin attributed 66% of the warming from long-lived greenhouse gases to carbon dioxide, 16% to methane and 6% to nitrous oxide. It assigned 8% to chlorofluorocarbons, 2% to hydrochlorofluorocarbons and 2% to hydrofluorocarbons.
What comes next
COP31 runs from November 9 to 20, 2026, in Antalya, Türkiye, the WMO said.
The WMO bulletin series began in 2004, according to the organization’s publication page.
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