GENEVA, Switzerland / EuroWire.IO / – Concentrations of carbon dioxide and other major greenhouse gases in the atmosphere reached record highs in 2025, the World Meteorological Organization said on October 27. The globally averaged surface concentration of CO2 rose to 426.8 parts per million. That is 153% of the pre-industrial level in 1750. Methane and nitrous oxide also reached new records, locking in further long-term warming. The WMO is the United Nations’ weather and climate agency.
The figures come from the WMO Greenhouse Gas Bulletin, one of the agency’s flagship annual reports. It measures concentrations of gases in the atmosphere rather than annual emissions. CO2 levels rose by 2.8 ppm between 2024 and 2025. That was above the average for the past decade but slightly below the surge recorded in 2023 to 2024. The first bulletin, published in 2004, recorded CO2 at 377.5 ppm.
WMO Deputy Secretary-General Ko Barrett called it another year with a new record. She said greenhouse gases are trapping an unprecedented amount of heat, fuelling more extreme weather and risks to economies and societies. Barrett noted that the past 11 years have been the warmest on record. She said CO2 will affect the climate for decades and even centuries because of its long lifetime. Barrett said the trend of record heat is set to continue.
Methane and nitrous oxide climb further
The global average concentration of methane reached 1,948 parts per billion in 2025, or 267% of the 1750 level. Methane accounts for about 16% of the warming effect of long-lived greenhouse gases. It stays in the atmosphere for a much shorter time than CO2. About 35% comes from natural sources such as wetlands. The remaining 65% comes from human activities, including cattle, rice farming, fossil fuels, landfills and biomass burning.
Nitrous oxide reached 339.1 ppb, or 126% of its pre-industrial level. It is the third most important long-lived greenhouse gas linked to human activity. Sources include biomass burning, fertiliser use and industrial processes, as well as natural emissions. Levels of sulphur hexafluoride also rose by a record amount in 2025. The gas is used in electricity distribution and has a lifetime of more than 1,000 years. Its warming potential is about 24,300 times that of CO2 over 100 years.
Further rise expected in 2026
WMO senior scientific officer Oksana Tarasova said growth in 2025 was more modest than a year earlier. Land carbon sinks recovered and emissions from fires fell after the 2023 to 2024 El Niño. She said the 2.8 ppm rise still marked a substantial addition of carbon from burning fossil fuels. The WMO expects concentrations to rise again in 2026 because of fossil fuel use and a developing El Niño.
The bulletin is published to inform negotiators ahead of the UN climate conference. The COP31 summit will take place in Antalya, Türkiye, from November 9 to 20 and aims to turn climate commitments into concrete action. About half of the CO2 emitted each year remains in the atmosphere, while oceans and land absorb the rest. Emissions in the European Union have fallen since 2015, according to official data.