Carbon dioxide averaged 426.8 parts per million in 2025, while methane and nitrous oxide also set records, the World Meteorological Organization (WMO) said, noting CO2's climate influence can extend for decades and centuries.
The 2025 addition was lower than the exceptional climb between 2023 and 2024. Against the 2016-25 period, however, it was faster than the average yearly gain, WMO said. The concentration was 53% above its estimated preindustrial level in 1750.
The other annual means were 1,948 parts per billion for methane and 339.1 parts per billion for nitrous oxide. WMO identifies wetlands as a natural methane source, alongside human activities such as cattle raising, rice farming and fossil fuel exploitation. Nitrous oxide comes from natural processes and human activity, including fertilizer use and industrial production.
WMO said stronger uptake by land carbon sinks and lower fire-related emissions helped moderate the CO2 increase after the 2023-24 El Niño, which brought drought, dry vegetation and wildfires. The agency's bulletin series recorded an annual CO2 average of 377.5 ppm in 2004. EconoTimes previously covered the 2025 concentration figures.
The bulletin reports the gases accumulated in the atmosphere, rather than the amount emitted in a single year. WMO estimates that about 50% of annual CO2 emissions stays in the air, with land ecosystems and oceans absorbing the rest.
The National Oceanic and Atmospheric Administration (NOAA) reported a separate measure: the heat-trapping influence of long-lived greenhouse gases, called radiative forcing, stood 56% above its 1990 benchmark in 2025. Carbon dioxide accounted for 81% of that increase in NOAA's Annual Greenhouse Gas Index.
“Every additional part per million matters because it traps additional heat,” WMO Deputy Secretary-General Ko Barrett said. For 2026, WMO forecasts a further rise in atmospheric CO2, pointing to continued fossil fuel burning and an emerging El Niño that may affect how much carbon land ecosystems absorb. The projection is not a full-year measurement. WMO publishes the bulletin to inform climate negotiators ahead of COP31, scheduled for Nov. 9-20 in Antalya, Türkiye.
