WMO: carbon dioxide hits a record 426.8 ppm in 2025, with COP31 in Antalya less than two weeks away

The amount of carbon dioxide in the atmosphere reached a new record in 2025, the World Meteorological Organization (WMO) said in its latest Greenhouse Gas Bulletin, and the UN weather agency warned that the effects will be felt for centuries. The findings were presented to journalists in Geneva on 27 October, less than two weeks before governments gather for the COP31 climate conference in Antalya, Turkey, from 9 to 20 November.

According to the bulletin, as reported by UN News, the global average concentration of carbon dioxide (CO2) in 2025 stood at 426.8 parts per million (ppm), or 153 percent of the level before industrialisation, which the WMO measures against 1750. Methane and nitrous oxide, the second and third most important long-lived greenhouse gases driven by human activity, also hit new peaks in 2025.

A faster rise than in the 1960s

The WMO said the pace of increase has accelerated sharply. When the bulletin series began in 2004, CO2 averaged 377.5 ppm. The annual growth rate has roughly tripled since the 1960s, from 0.8 ppm per year then to 2.4 ppm per year in the decade 2011 to 2020. Between 2023 and 2024 the concentration rose by 3.5 ppm, a jump that coincided with a strong El Niño. The agency said drought and wildfires reduced the ability of land vegetation to absorb carbon in that period, a point explained by WMO senior scientific officer Oksana Tarasova. From 2024 to 2025 CO2 rose by 2.8 ppm, and the WMO expects a further increase in 2026.

Speaking in Geneva, WMO Deputy Secretary-General Ko Barrett stressed why each increment counts: “Every additional part per million matters because it traps additional heat.” The agency noted that carbon dioxide stays in the atmosphere for decades to centuries, and that about half of the CO2 emitted each year remains in the air while the rest is taken up by land and oceans. The past 11 years were the warmest on record, the WMO said.

Other gases and the warming index

The bulletin also points to gases that receive less public attention. Sulphur hexafluoride (SF6), used in electrical equipment, has an atmospheric lifetime of more than 1,000 years and a 100-year warming potential about 24,300 times that of CO2, and its 2025 increase was a record, according to the figures relayed by UN News. Hydrogen concentrations rose by 5.3 percent between 2010 and 2024, a trend the WMO raised in the context of the energy transition.

The WMO also cited the Annual Greenhouse Gas Index of the U.S. National Oceanic and Atmospheric Administration (NOAA). It shows that the warming effect of long-lived greenhouse gases rose by 56 percent from 1990 to 2025, with carbon dioxide responsible for about 81 percent of that increase.

What comes next

The bulletin is intended to inform negotiators at COP31, which opens in Antalya on 9 November and runs until 20 November. The figures add to the pressure on delegations over emissions cuts, finance and energy security. The WMO did not set out any new policy proposal in the material released on 27 October; its role is to publish the measurements that the negotiations rely on.