Carbon dioxide reached a record 426.8 ppm in 2025, WMO bulletin says

The amount of carbon dioxide in the atmosphere reached a new high of 426.8 parts per million (ppm) in 2025, the World Meteorological Organization (WMO) said on October 27, 2026, in its annual Greenhouse Gas Bulletin. That is 153% of the level in 1750, before industrialization. Methane and nitrous oxide, the second and third most important long-lived greenhouse gases linked to human activity, also set records.

CO2 rose by 2.8 ppm from 2024 to 2025. That was smaller than the unusually large jump from 2023 to 2024 but a little above the average yearly rise over the decade from 2016 to 2025, the bulletin says.

Why growth eased slightly, and why it may pick up

WMO senior scientific officer Oksana Tarasova linked the more modest 2025 increase to a recovery of land carbon sinks and lower fire emissions after the strong 2023-2024 El Niño, which brought more drought, drier vegetation and more wildfires. She cautioned that “a 2.8 ppm annual increase is still a substantial addition of carbon to the atmosphere from fossil fuel burning.”

Tarasova said WMO expects levels to climb again in 2026, driven by continued fossil fuel burning and a strong El Niño now developing, which she said will affect land carbon sinks as the last one did in 2023-2024.

Over the longer run, the trend is steeper. WMO says CO2 growth rates have tripled since the 1960s, from an average of 0.8 ppm a year to 2.4 ppm a year in the decade from 2011 to 2020. When the bulletin was first published, in 2004, the annual average CO2 level was 377.5 ppm.

Concentrations are not emissions

The bulletin measures how much of each gas has built up in the air, not how much was emitted in a given year. About half of the CO2 released each year stays in the atmosphere, and land ecosystems and oceans absorb the rest, WMO says. That is why, as Tarasova noted, a recovery of land sinks can slow the rise in a single year even while fossil fuel use continues.

Other agencies measure the same gases with their own networks. The US National Oceanic and Atmospheric Administration (NOAA), which samples air at remote sites, put the 2025 global average for CO2 at 425.62 ppm and measured a rise of 2.06 ppm between January 1, 2025, and January 1, 2026. WMO's analysis draws on observations from 179 stations and compares annual averages, so the two agencies' figures are not directly interchangeable. NOAA's Annual Greenhouse Gas Index found that the warming effect of long-lived greenhouse gases was 56% greater in 2025 than in 1990, with CO2 responsible for about 81% of the increase.

Two smaller gases to watch

WMO also flags two potent but less abundant gases closely tied to electricity and the energy transition. Sulfur hexafluoride (SF6), used mainly as a spark suppressant in electricity distribution, lasts more than 1,000 years in the atmosphere and has a 100-year warming potential about 24,300 times that of CO2. Its increase in 2025 was a record.

WMO says hydrogen is not itself a greenhouse gas, but its influence on the chemistry of the atmosphere gives it a strong indirect warming effect. Its concentration rose 5.3% between 2010 and 2024. Hydrogen is being used in hard-to-decarbonize sectors such as steelmaking and shipping, and for long-duration energy storage, so leaks from production plants, pipelines, storage tanks and fuel cells are a growing concern.

What comes next

WMO publishes the bulletin to give negotiators at the UN climate conference authoritative data. This year's conference, COP31, takes place in Antalya, Türkiye, from November 9 to 20, 2026. The measurements behind the bulletin are archived by the World Data Centre for Greenhouse Gases at the Japan Meteorological Agency.