Concentrations of the three main greenhouse gases in the atmosphere hit record highs in 2025, the United Nations weather and climate agency said on Tuesday, warning that the consequences will persist for centuries.
The World Meteorological Organization (WMO) reported that carbon dioxide, methane and nitrous oxide all reached unprecedented levels. The agency said the increase will drive further long-term temperature rises across the planet. Its 22nd annual Greenhouse Gas Bulletin was released ahead of the COP31 U.N. climate summit, scheduled for Nov. 9 to Nov. 20 in Antalya, Turkey.
"Another year, another new record," said WMO Deputy Secretary-General Ko Barrett. She said greenhouse gases are trapping an unprecedented amount of heat, providing energy for more extreme weather and related risks to economies and societies. Barrett noted that the past 11 years have been the warmest on record and that the trend is expected to continue. Because carbon dioxide has a very long lifetime, she said, it will affect the climate for decades and even centuries.
The bulletin measures how much of each gas is present in the atmosphere, rather than the yearly amount of new emissions from burning coal, oil and gas. In 2025, carbon dioxide stood at 426.8 parts per million, methane at 1,948 parts per billion and nitrous oxide at 339.1 parts per billion. Those figures equal 153%, 267% and 126% of pre-industrial levels from before 1750.
Carbon dioxide accounts for about 66% of the warming effect among the three major gases. Roughly half of the carbon dioxide released each year stays in the atmosphere, while land and oceans absorb the remainder.
The global average concentration of carbon dioxide grew by 2.8 ppm from 2024 to 2025. That was less than the record jump of 3.6 ppm between 2023 and 2024. WMO senior scientific officer Oksana Tarasova attributed the smaller rise to the "recovery of the land carbon sinks and reduced fire carbon emissions in 2025 after the strong 2023/2024 El Nino." She cautioned, however, that 2.8 ppm is still a substantial addition of carbon from fossil fuel burning. It also exceeds the average growth rate of the past decade, 2.6 ppm, and compares with 0.8 ppm in the 1960s.
Tarasova said further increases are expected in 2026 because of continued fossil fuel use and the development of a powerful El Nino, which will affect land carbon sinks as it did in 2023/2024.
Methane contributes about 16% of the warming effect from long-lived greenhouse gases, although it persists in the atmosphere for a much shorter time than carbon dioxide. About a third of methane emissions come from natural sources such as wetlands. The rest comes from human activity, including cattle, rice farming, landfills and biomass burning.
The bulletin also urged greater attention to two potent but less abundant trace gases linked to electricity production and distribution as countries move toward decarbonization: molecular hydrogen and sulfur hexafluoride. Sulfur hexafluoride, used mainly as a spark suppressant in electricity distribution, has risen steadily over three decades. The reason hydrogen levels have climbed over the past decade is unknown, though it has begun to be used as an energy storage medium.
