Greenhouse gases hit new record levels in 2025, WMO bulletin says

The three main greenhouse gases reached their highest recorded concentrations in the atmosphere in 2025, the World Meteorological Organization (WMO), the UN weather and climate agency, said on Tuesday. It said the rise will lead to further long-term temperature increases and lock in climate impacts that will last for centuries.

The findings are in the WMO's 22nd annual Greenhouse Gas Bulletin. It was released ahead of the COP31 UN climate summit, which will be held in Antalya, Turkey, from 9 to 20 November. The bulletin measures the concentrations of gases in the atmosphere, not the amounts emitted each year.

The global average concentration of carbon dioxide was 426.8 parts per million (ppm) in 2025. Methane stood at 1,948 parts per billion (ppb) and nitrous oxide at 339.1 ppb. According to the bulletin, these are 153%, 267% and 126% of pre-industrial levels from before 1750. New Scientist described the CO2 level as 53 per cent above the pre-industrial level.

Carbon dioxide rose by 2.8 ppm between 2024 and 2025. That is smaller than the record jump of 3.6 ppm from 2023 to 2024, but above the average growth rate of the past decade, 2.6 ppm. In the 1960s the figure was 0.8 ppm. WMO senior scientific officer Oksana Tarasova said the smaller rise reflected the recovery of land carbon sinks and reduced fire emissions after the strong 2023/2024 El Nino. She added that 2.8 ppm is still a substantial addition from fossil fuel burning, and that concentrations are expected to rise further in 2026 because of fossil fuel use and a developing powerful El Nino.

CO2 accounts for about 66% of the warming effect of long-lived greenhouse gases, and around half of the CO2 emitted each year stays in the atmosphere, with the rest absorbed by land and oceans. Methane accounts for about 16% of the warming effect and has a much shorter lifetime. About a third of methane comes from natural sources such as wetlands; the rest comes from sources such as cattle, rice farming, landfills and biomass burning.

WMO Deputy Secretary-General Ko Barrett said, "Another year, another new record." She said greenhouse gases are trapping an unprecedented amount of heat, providing energy for more extreme weather and risks to economies and societies, and that the past 11 years have been the warmest on record.

The bulletin also says more attention should be paid to molecular hydrogen and sulphur hexafluoride as countries decarbonise their energy systems. Hydrogen is not a greenhouse gas but has a strong indirect warming effect, and its concentration rose 5.3 per cent between 2010 and 2024. The reason for the rise is unknown, though it has begun to be used for energy storage. Sulphur hexafluoride, used mainly as a spark suppressant in electricity distribution, has risen steadily for three decades and has a 100-year warming potential about 24,000 times that of CO2, according to the WMO.