The air we breathe now carries more heat-trapping gas than at any time since humans began measuring it systematically, the World Meteorological Organization reported in Geneva on Tuesday. Its yearly Greenhouse Gas Bulletin reports an average CO2 level of 426.8 ppm across the globe in 2025. That is roughly one and a half times what the atmosphere contained in 1750. When the agency printed its first edition in 2004, the figure stood at 377.5.
Methane and nitrous oxide, the next two long-lived culprits, also set fresh highs. Methane reached 1,948 parts per billion, more than two and a half times its pre-industrial level, with roughly two thirds of it traced to human activities such as livestock, rice paddies, landfills and fossil fuel extraction. Nitrous oxide, largely linked to fertiliser and industry, rose to 339.1 ppb.
There is a small footnote of relief. The CO2 increase slowed to 2.8 ppm from the extraordinary 3.5 ppm jump between 2023 and 2024. WMO scientist Oksana Tarasova credits forests and soils, which soaked up more carbon once the strong El Niño of those years, with its droughts and wildfires, had passed. She warned against reading too much into it, calling the latest rise “a substantial addition of carbon” and predicting further growth in 2026 as another powerful El Niño takes shape.
Deputy Secretary-General Ko Barrett was blunter: “Another year, another new record.” The last eleven years have all ranked as the hottest on record, she said, and because carbon dioxide lingers so long, today’s pollution will shape the climate for generations.
The bulletin tracks what builds up in the sky rather than what is emitted each year, since oceans and land absorb about half of all CO2 released. It is designed as a reference for negotiators heading to the COP31 climate summit in Antalya, Türkiye, which runs from 9 to 20 November.
