Atmospheric concentrations of the three main greenhouse gases reached record levels in 2025, according to the latest bulletin from the World Meteorological Organization (WMO). Carbon dioxide, methane and nitrous oxide are now trapping more heat and contributing energy to extreme climate phenomena.
The bulletin was published to provide scientific information for negotiators attending the 31st Conference of the Parties on climate, COP31, scheduled to take place in Antalya, Türkiye, from 9 to 20 November.
Global average carbon dioxide concentration reached 426.8 parts per million, while methane stood at 1,948 parts per billion and nitrous oxide at 339.1 parts per billion. Compared with pre-industrial levels, before 1750, these figures represent increases of 53%, 167% and 26%, respectively.
The WMO cautions that the sequence of records may continue because the figures describe the accumulated concentration of greenhouse gases rather than annual emissions. Carbon dioxide can remain in the atmosphere for long periods. Around half of the CO2 emitted each year stays in the atmosphere, while the rest is absorbed by the oceans and terrestrial ecosystems.
The rate of CO2 accumulation has tripled since the 1960s, rising from an average annual increase of 0.8 parts per million to 2.4 parts per million during the 2011–2020 decade. Between 2024 and 2025, the global average concentration increased by 2.8 parts per million. That was above the recent decadal average but slightly below the 3.5-part-per-million increase recorded between 2023 and 2024.
Oksana Tarasova, a WMO scientific official, attributed the more moderate increase to the recovery of terrestrial carbon sinks and lower fire-related carbon emissions after the strong 2023–2024 El Niño. That event had reduced the biosphere’s efficiency through greater drought, drier vegetation and more wildfires. The WMO considers it plausible that concentration growth could accelerate in 2026, partly because of the super El Niño’s effects on land carbon sinks.
The bulletin also highlights the difference between slowing emissions and stabilizing atmospheric concentrations. As explained by Maurizio Maugeri, professor of Earth, planetary, space and climate system physics at the University of Milan, emissions cuts would first reduce the rate at which CO2 concentrations rise. Concentrations would begin to stabilize only once net-zero emissions were achieved, meaning that incoming CO2 no longer exceeded the amount absorbed by the Earth and, where possible, removed through technological methods.
Between 1990 and 2025, the warming effect on the climate from greenhouse gases increased by 56%. Carbon dioxide accounted for 81% of that effect, while methane contributed 16%. Methane remains in the atmosphere for considerably less time than CO2 and comes from both human activities and natural systems. Major human sources include livestock farming, rice cultivation, fossil fuel use, landfill emissions and biomass burning; natural sources include marshes and peatlands.
Nitrous oxide is associated with industrial processes, fertilizer use and biomass combustion. The WMO bulletin also calls for closer monitoring of two other long-lived gases linked to electricity production and distribution, whose concentrations could rise as decarbonization progresses.
Molecular hydrogen, or H2, is used for energy storage and is not itself a greenhouse gas. However, it affects atmospheric chemistry in ways that can indirectly promote global warming. Its concentration increased by 5.3% between 2010 and 2024, raising concerns about leaks from pipelines and production and storage facilities.
The second gas is sulfur hexafluoride, or SF6, which is used to suppress sparks in electricity distribution. Its atmospheric levels have risen steadily over the past three decades. SF6 can remain in the atmosphere for around a thousand years and has a 100-year global warming potential approximately 24,300 times greater than that of CO2.
Monitoring atmospheric composition in the coming years will help assess whether the benefits of the energy transition are being reduced by gases with unwanted climate effects.
Sources: Focus.it.