WMO says three major greenhouse gases reached record atmospheric levels in 2025
Carbon dioxide reached a global average of 426.8 parts per million, the UN weather agency said, adding to warming that will affect the climate for decades and centuries.
The World Meteorological Organization said on 27 October 2026 that atmospheric concentrations of carbon dioxide, methane and nitrous oxide all reached records in 2025. The global average for carbon dioxide was 426.8 parts per million, a level the UN weather agency said will add to warming for decades and centuries.
What the 2025 greenhouse gas figures measure
Carbon dioxide stood at 153% of its 1750 pre-industrial baseline, according to the WMO bulletin. AFP reported that methane reached 1,948 parts per billion, or 267% of its pre-industrial level, while nitrous oxide reached 339.1 parts per billion, or 126% of its baseline. The figures describe concentrations of gases already accumulated in the atmosphere; they are not a measure of new emissions during 2025.
The global average carbon dioxide concentration rose by 2.8 parts per million from 2024 to 2025. AFP reported that this was below the 3.6-part-per-million rise in the preceding year, but above the past decade’s average annual increase of 2.6 parts per million. A slower increase than the previous year therefore still left the atmospheric concentration at a new high.
The WMO said roughly half the carbon dioxide emitted each year remains in the atmosphere; land ecosystems and oceans absorb the rest. The persistence of carbon dioxide helps explain why the agency says today’s concentrations will affect the climate long after the year in which the emissions occurred.
Why WMO says the records matter
“Every additional part per million matters because it traps additional heat,” WMO Deputy Secretary-General Ko Barrett told journalists in Geneva, according to UN News. Barrett said the added heat affects the ocean and atmosphere, intensifying heatwaves, tropical cyclones and rainstorms beyond historical baselines. That is the agency’s assessment of the broader climate risk, rather than a finding about the cause of any particular weather event.
WMO also expects concentrations to rise further in 2026. It attributed that outlook to continued fossil-fuel burning and the development of a powerful El Niño, which it said could affect the capacity of land ecosystems to absorb carbon dioxide, as happened in 2023 and 2024.
The bulletin comes ahead of the COP31 climate conference, scheduled for 9–20 November 2026 in Antalya, Türkiye. Its distinction between annual emissions and accumulated atmospheric gases matters for interpreting the new records: even when the yearly rise in carbon dioxide slows, the concentration can continue to climb.
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Sources and context
- Record carbon dioxide levels will impact us for centuries, says UN weather agencyUN News
- Greenhouse gas levels hit new record highs in 2025 - UNAgence France-Presse, published by RTÉ
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