GENEVA, Switzerland / EuroWire.IO / – Carbon dioxide in the atmosphere climbed to a record 426.8 parts per million in 2025, according to a new report from the World Meteorological Organization. The UN weather agency said concentrations of methane and nitrous oxide also hit new highs. CO2 levels now stand at 153% of the pre-industrial baseline set in 1750. The WMO said the rise locks in more long-term warming for the planet.
The findings were published in the WMO Greenhouse Gas Bulletin on October 27. The annual report tracks how much of each gas remains in the atmosphere. CO2 increased by 2.8 ppm from 2024 to 2025, the WMO said. Growth over the decade from 2011 to 2020 averaged 2.4 ppm a year, three times the rate of the 1960s. About half of each year’s CO2 emissions stay in the air.
Ko Barrett, the WMO’s Deputy Secretary-General, said greenhouse gases are trapping an unprecedented amount of heat. She said this provides energy for more extreme weather and creates risks for economies and societies. According to Barrett, the past 11 years have been the warmest ever recorded and the trend is set to continue. CO2 has a very long lifetime and will affect the climate for decades or centuries, she said.
Methane reaches 267% of pre-industrial level
Methane concentrations averaged 1,948 ppb in 2025, equal to 267% of the 1750 level. The gas is responsible for about 16% of the warming caused by long-lived greenhouse gases. Around 65% of methane comes from human sources, including livestock, rice cultivation, fossil fuel production, landfills and biomass burning. The other 35% is released by natural sources such as wetlands, which are themselves sensitive to climate. Methane stays in the atmosphere for a much shorter time than CO2.
Nitrous oxide rose to 339.1 ppb, which is 126% of its 1750 level. It ranks as the third most important long-lived greenhouse gas tied to human activity. Fertiliser use, biomass burning and industrial processes add to natural sources of the gas. The WMO also reported a record increase in sulphur hexafluoride, used as a spark suppressant in power networks. Its warming potential is about 24,300 times that of CO2.
Bulletin published ahead of COP31
The WMO said concentrations are expected to rise further in 2026. It cited continued fossil fuel burning and a developing strong El Niño, which could weaken land carbon sinks as in 2023 and 2024. Oksana Tarasova, a senior scientific officer at the agency, said growth slowed in 2025 as sinks recovered and fire emissions fell. She said the increase still showed a large addition of carbon from fossil fuels.
The bulletin is designed to give negotiators authoritative scientific information before the UN climate talks. COP31 will be held in Antalya, Türkiye, from November 9 to 20. The meeting aims to turn climate pledges into concrete actions. Oceans and land ecosystems absorb roughly half of the CO2 emitted each year. In Europe, EU greenhouse gas emissions edged higher in the first quarter of 2026, official data showed.