Greenhouse gas concentrations in the atmosphere reached record highs in 2025, according to the United Nations’ weather agency. The World Meteorological Organization (WMO) reported that levels of carbon dioxide (CO2), methane, and nitrous oxide all rose to unprecedented figures, locking in long-term climate impacts.
The WMO’s annual Greenhouse Gas Bulletin, released ahead of the upcoming COP31 climate summit in Antalya, Turkey, confirmed that CO2 concentrations reached 426.8 parts per million (ppm)—153% of pre-industrial levels. Methane and nitrous oxide also hit record concentrations of 1,948 parts per billion and 339.1 parts per billion, respectively.
Immediate impacts and long-term consequences
The WMO emphasized that these record levels will drive centuries of warming, as greenhouse gases trap heat in the atmosphere. Ko Barrett, WMO Deputy Secretary-General, stated: “Another year, another new record. Greenhouse gases are trapping an unprecedented amount of heat, fueling more extreme weather and risks to economies and societies.”
The bulletin measures atmospheric concentrations rather than annual emissions, meaning the data reflects the cumulative effect of past and present emissions. CO2 accounts for about 66% of the warming effect, with roughly half of emitted CO2 remaining in the atmosphere while the rest is absorbed by land and oceans.
Year-over-year trends and variability
While CO2 growth rates have accelerated since the 1960s, the 2024–2025 increase of 2.8 ppm was slightly lower than the 3.6 ppm surge from 2023–2024. WMO scientists attributed this moderation to recovery in land carbon sinks and reduced wildfire emissions following the strong 2023–2024 El Niño, which had weakened biosphere efficiency through drought and increased fires.
Despite global commitments to Net Zero targets and renewable energy expansion, the data shows no decline in greenhouse gas concentrations. The WMO noted that CO2 growth rates tripled from 0.8 ppm per year in the 1960s to 2.4 ppm per year between 2011 and 2020, signaling persistent challenges in mitigation efforts.
Policy context and upcoming climate negotiations
The findings come ahead of the COP31 summit, scheduled for November 9–20 in Antalya, where nations are expected to review progress on climate pledges under the Paris Agreement. The WMO’s report underscores the urgency of reducing emissions, as the long lifespan of CO2 means its effects will persist for decades and centuries.
Key figures from the report:
- CO2: 426.8 ppm (153% of pre-industrial levels)
- Methane: 1,948 ppb (267% of pre-industrial levels)
- Nitrous oxide: 339.1 ppb (126% of pre-industrial levels)
- CO2 growth (2024–2025): 2.8 ppm (down from 3.6 ppm in 2023–2024)
The data reinforces warnings that current trajectories are insufficient to meet global temperature goals, with the WMO stressing that immediate and sustained action is required to alter long-term warming trends.