Greenhouse gas concentrations in the atmosphere reached new record highs in 2025, according to a report released Tuesday by the United Nations. The World Meteorological Organization (WMO) highlighted that levels of the three primary greenhouse gases—carbon dioxide, methane, and nitrous oxide—continued to climb, contributing to climate impacts expected to persist for centuries.
The WMO’s 22nd annual Greenhouse Gas Bulletin reported that in 2025, carbon dioxide (CO2) concentrations averaged 426.8 parts per million (ppm), methane reached 1,948 parts per billion, and nitrous oxide was measured at 339.1 parts per billion. These figures represent increases to 153%, 267%, and 126% respectively, relative to pre-industrial levels before 1750.
CO2 remains the dominant driver of climate warming among these gases, contributing approximately 66% of the long-lived greenhouse gas effect. Around half of the CO2 emitted annually remains in the atmosphere, while the rest is absorbed by terrestrial and oceanic systems. From 2024 to 2025, the global CO2 concentration grew by 2.8 ppm, which, while lower than the 3.6 ppm increase recorded between 2023 and 2024, still reflects a substantial annual addition of carbon from fossil fuel combustion. This growth rate exceeds the average increase of 2.6 ppm observed over the past decade and is significantly higher than the 0.8 ppm annual rise seen in the 1960s.
WMO senior scientific officer Oksana Tarasova attributed the slowdown in CO2 growth between 2024 and 2025 to the "recovery of the land carbon sinks and reduced fire carbon emissions" following the strong El Niño event during 2023-2024—a natural climate phenomenon known to influence atmospheric conditions. Nevertheless, she emphasized that the addition of 2.8 ppm still represents a significant infusion of greenhouse gases due to fossil fuel use.
Methane, which accounts for about 16% of the warming effect from long-lived greenhouse gases, has a shorter atmospheric lifetime compared to CO2. Approximately one-third of methane emissions originate from natural sources such as wetlands, while the majority come from human activities including livestock farming, rice cultivation, landfills, and biomass burning. Nitrous oxide, responsible for roughly 6% of greenhouse gas-driven warming, also increased in concentration during 2025.
WMO deputy secretary-general Ko Barrett stated that greenhouse gases are trapping an unprecedented amount of heat, fueling more intense and frequent extreme weather events such as heatwaves, tropical cyclones, and heavy rainfall. He noted that “the past 11 years have been the warmest on record,” a trend expected to continue.
The bulletin’s release precedes the upcoming COP31 United Nations climate summit, scheduled from November 9 to 20 in Antalya, Turkey. The report also draws attention to less abundant but potent trace gases related to energy systems, including molecular hydrogen and sulphur hexafluoride, which may require increased focus as countries advance decarbonization efforts.
Overall, the findings underline the persistent challenge in limiting greenhouse gas concentrations and mitigating long-term climate change impacts worldwide.