This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Levels of carbon dioxide (CO₂) and other major greenhouse gases in the atmosphere reached unprecedented highs in 2025, locking in more long-term warming for the planet, according to a new report from the World Meteorological Organization (WMO). The WMO Greenhouse Gas Bulletin reported that the globally averaged surface concentration of CO₂ in 2025 was 426.8 parts per million, or 153% of the 1750 preindustrial baseline.
Concentrations of methane and nitrous oxide—the second and third most important long-lived greenhouse gases related to human activities—also rose to record highs. "Another year, another new record. Greenhouse gases are trapping an unprecedented amount of heat in the atmosphere, providing energy for more extreme weather and associated risks to our economies and societies.
The past 11 years have been the warmest on record and this trend is set to continue. CO₂ has a very long lifetime and so will affect the global climate not just for years but for decades and even centuries," said WMO Deputy Secretary-General Ko Barrett. WMO releases the bulletin, one of its flagship annual publications, to provide authoritative scientific information for negotiators at the U.N. climate conference.
The COP 31 meeting in Antalya, Turkey, Nov. 9–20 is seeking to turn climate commitments into concrete actions. The bulletin reports on greenhouse gas concentrations—namely the amount of gas that accumulates in the atmosphere—and not new annual emissions. About half of the total CO₂ emitted each year remains in the atmosphere, and the rest is absorbed by Earth's land ecosystems and oceans.
When the bulletin was first published in 2004, the annual average level of CO₂ measured by WMO's Global Atmosphere Watch network of monitoring stations was 377.5 ppm. The National Oceanic and Atmospheric Administration (NOAA) Annual Greenhouse Gas Index shows that from 1990 to 2025, radiative forcing—the warming effect on our climate—by long-lived greenhouse gases increased by 56%, with CO₂ accounting for about 81% of this increase. Growth rates of CO₂ have tripled since the 1960s, accelerating from an annual average increase of 0.8 ppm to 2.4 ppm in the decade from 2011 to 2020.
From 2024 to 2025, the global average concentration of CO₂ rose by 2.8 ppm—above the decadal average but slightly less than the exceptional surge of 2023/2024. "The more modest growth rate from 2024 to 2025 reflects recovery of the land carbon sinks and reduced fire carbon emissions in 2025 after the strong 2023/2024 El Niño, which reduced the efficiency of the biosphere through more drought, drier vegetation and more wildfires," said WMO senior scientific officer Oksana Tarasova. "However, a 2.8 ppm annual increase is still a substantial addition of carbon to the atmosphere from fossil fuel burning.
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