Atmospheric Heat-Trapping Gases Hit New Highs in 2025, WMO Reports

Greenhouse gas concentrations in the atmosphere reached record levels in 2025, a development the United Nations says will influence global temperatures for centuries. The World Meteorological Organization released its annual findings from Geneva on Tuesday, noting that the rise will lead to further long-term temperature increases.

The WMO's 22nd annual Greenhouse Gas Bulletin reports that concentrations of carbon dioxide, methane, and nitrous oxide all rose to record figures last year. Carbon dioxide levels were recorded at 426.8 parts per million, methane at 1,948 parts per billion, and nitrous oxide at 339.1 parts per billion. When compared to pre-industrial levels from before 1750, these figures represent 153%, 267%, and 126% respectively. Carbon dioxide contributes about 66% of the warming effect on the climate.

The growth rate for carbon dioxide slowed slightly compared to the previous year, though it remained above the decade's average. Global average CO2 concentrations increased by 2.8 ppm between 2024 and 2025, down from the 3.6 ppm jump recorded from 2023 to 2024. This rate still exceeds the 10-year average of 2.6 ppm, a figure that stood at 0.8 ppm in the 1960s. Oksana Tarasova, a senior scientific officer at the WMO, attributed the slower rise to the recovery of land carbon sinks and reduced fire emissions following the strong 2023/2024 El Nino.

Despite the smaller annual increase, Tarasova stated that a 2.8 ppm rise represents a substantial addition of carbon to the atmosphere from fossil fuel burning. She warned that concentrations will continue to rise in 2026 due to ongoing fossil fuel use and the development of a powerful El Nino that will affect land carbon sinks, similar to the impact seen in 2023/2024. The bulletin notes that approximately half of the CO2 emitted each year remains in the atmosphere, while the rest is absorbed by land and oceans.

The report also examines gases associated with electricity production and distribution as nations shift their energy systems toward decarbonization. Sulfur hexafluoride (SF6), used primarily as a spark suppressant in electricity distribution, has risen steadily over the past three decades. Molecular hydrogen (H2) has also increased over the last decade, though the WMO states the reason for this rise is unknown; hydrogen has begun to be used as an energy storage medium.

WMO Deputy Secretary-General Ko Barrett characterized the situation by saying, "Another year, another new record." She noted that greenhouse gases are trapping heat in the atmosphere, providing energy for extreme weather and associated risks to economies and societies. Barrett added that the past 11 years have been the warmest on record and that carbon dioxide has a long lifetime, affecting the global climate for decades and centuries. The bulletin was released ahead of the COP31 U.N. climate summit scheduled for Antalya, Turkey, from Nov. 9 to Nov. 20.