GENEVA, 27th October, 2026 (WAM) -- Levels of carbon dioxide (CO2) and other major greenhouse gases in the atmosphere reached unprecedented highs in 2025, locking in more long-term temperature increase for the planet, according to a new report from the World Meteorological Organisation (WMO).
The WMO Greenhouse Gas Bulletin reported that the globally averaged surface concentration of CO2 in 2025 was 426.8 parts per million, or 153% of the 1750 pre-industrial baseline. Concentrations of methane and nitrous oxide - the second and third most important long-lived greenhouse gases related to human activities - also rose to a new record.
“Another year, another new record. Greenhouse gases are trapping an unprecedented amount of heat in the atmosphere, providing energy for more extreme weather and associated risks to our economies and societies. The past 11 years have been the warmest on record and this trend is set to continue. CO2 has a very long life-time and so will affect the global climate not just for years but for decades and even centuries,” said WMO Deputy Secretary-General Ko Barrett.
WMO releases the Bulletin, one of its flagship annual publications, to provide authoritative scientific information for negotiators at the UN Climate conference. The COP 31 meeting in Antalya, Türkiye, from 9-20 November 2026 is seeking to turn climate commitments into concrete actions.
Methane accounts for about 16% of the warming effect on our climate by long-lived greenhouse gases but it has a much shorter lifetime than CO2. Approximately 35% of methane is emitted into the atmosphere by natural sources (for example, wetlands) which are sensitive to climate as well, and about 65% comes from anthropogenic sources such as cattle, rice farming, fossil fuel exploitation, landfills and biomass burning.
The globally averaged methane concentration in 2025 was 1948 parts per billion (ppb) – or 267% of the 1750 level.
Nitrous oxide is the third most important long-lived greenhouse gas and comes from both natural sources and due to human activities such as biomass burning, fertilizer use and various industrial processes.
The globally averaged concentration of N2O reached 339.1 ppb in 2025, 126% above 1750.