Atmospheric concentrations of carbon dioxide, methane and nitrous oxide all reached record levels in 2025, according to the World Meteorological Organization's latest annual Greenhouse Gas Bulletin.
The United Nations weather and climate agency measured global average carbon dioxide at 426.8 parts per million. Methane reached 1,948 parts per billion and nitrous oxide 339.1 parts per billion. Those levels corresponded to 153%, 267% and 126% of their respective pre-industrial concentrations before 1750.
The bulletin measures the amount of each gas accumulated in the atmosphere, which is different from annual emissions. Concentrations reflect continuing human releases as well as the portion absorbed by land and oceans. Roughly half of carbon dioxide emitted in a year remains in the atmosphere, according to the report summarized by AFP.
Carbon dioxide rose by 2.8 parts per million between 2024 and 2025. That was below the previous year's record 3.6 ppm increase but above the past decade's average annual growth of 2.6 ppm. WMO senior scientific officer Oksana Tarasova attributed the slower rise compared with the prior year to recovering land carbon sinks and reduced fire emissions following the strong 2023–2024 El Niño, while stressing that the increase still represented a substantial addition from fossil-fuel use.
Carbon dioxide accounts for about two-thirds of the warming influence from long-lived greenhouse gases and can affect climate for centuries. Methane contributes about 16% and remains in the atmosphere for less time, making reductions potentially important on a shorter horizon. The WMO said about one-third of methane emissions come from natural sources such as wetlands, with the remainder linked to activities including livestock, rice cultivation, landfills and biomass burning.
The agency also drew attention to less abundant gases connected with energy systems. Sulfur hexafluoride, used in electricity distribution, has increased steadily for three decades. WMO deputy secretary-general Ko Barrett said it can persist for as long as 3,200 years and has a warming potential more than 24,000 times that of carbon dioxide. The bulletin also noted rising molecular hydrogen levels, though the reason for the recent increase remains uncertain.
Monitoring stations showed carbon dioxide continuing to rise in 2026. Because each additional increment traps more heat, the WMO linked the accumulation to higher long-term temperatures and greater energy in the atmosphere and oceans.
The findings were released ahead of the COP31 climate summit scheduled in Antalya, Turkey, from November 9 to 20. They underscore that year-to-year variations in growth do not change the central trend: the stock of heat-trapping gases is still increasing, extending climate effects well beyond the year in which emissions occur.
