Record greenhouse gases trap more heat, WMO warns

The World Meteorological Organization reported on Tuesday that the atmosphere held record greenhouse gases in 2025, with carbon dioxide, methane and nitrous oxide all reaching new highs.

The finding comes from the agency's annual Greenhouse Gas Bulletin, compiled from its Global Atmosphere Watch network of monitoring stations. The bulletin measures gases that have accumulated in the atmosphere, not emissions in a single year. About half of the carbon dioxide emitted each year stays in the air, while land ecosystems and oceans absorb the rest, according to the report.

Carbon dioxide averaged 426.8 parts per million at the surface last year, or 153 per cent of the pre-industrial level recorded in 1750. When the bulletin was first published in 2004, the average stood at 377.5 parts per million.

This is the 22nd edition of the bulletin, which tracks the gases that trap heat in the atmosphere over decades. Carbon dioxide accounts for about 66 per cent of the warming effect of the three main gases combined, the bulletin says, because it persists in the air far longer than methane or nitrous oxide and because so much of it is emitted.

Methane reached 1,948 parts per billion, or 267 per cent of its pre-industrial level. Nitrous oxide climbed to 339.1 parts per billion, or 126 per cent of the level before industrialisation. Both gases rose to new peaks alongside carbon dioxide, according to the bulletin.

The numbers behind the new highs

The pace of increase has quickened sharply over the decades. Annual carbon dioxide growth averaged 0.8 parts per million in the 1960s and 2.4 parts per million between 2011 and 2020. The rise last year was smaller than the jump of the year before, a slowdown the agency links to recovering land carbon sinks and lower fire emissions after the strong El Nino of recent years.

Senior scientific officer Oksana Tarasova put the slowdown in context: "However, a 2.8 ppm annual increase is still a substantial addition of carbon to the atmosphere from fossil fuel burning."

The agency expects concentrations to climb further in 2026, driven by continued fossil fuel use and a powerful El Nino that could weaken land carbon sinks again, as it did during the previous strong event. Readers following the Pacific pattern can see how this year's event is already reshaping conditions in Super El Nino Turns Pacific Waters Bluer From Space.

A longer shadow than one year

Deputy Secretary-General Ko Barrett told journalists in Geneva that the gases are "trapping an unprecedented amount of heat in the atmosphere" and providing energy for more extreme weather, with associated risks to economies and societies. "Another year, another new record," Barrett said.

Barrett added that the past 11 years have been the warmest on record and that the 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," Barrett said.

The United States National Oceanic and Atmospheric Administration's Annual Greenhouse Gas Index found that the warming effect of greenhouse gases rose 56 per cent between 1990 and last year, with carbon dioxide accounting for about 81 per cent of that increase.

The consequences are visible in the cryosphere as well as the atmosphere: Greenland Ice Sheet Loses Ice for 30th Year Straight documents a melt trend running in parallel with the gas records.

What negotiators face in Antalya

The bulletin lands shortly before the COP31 UN climate conference, scheduled for 9 to 20 November in Antalya, Turkiye, where negotiators are due to turn climate commitments into concrete actions.

The report also flags a pair of trace gases tied to the energy transition. Sulphur hexafluoride, used mainly as insulation in electricity distribution equipment, recorded its largest annual increase last year. The gas can linger in the air for well over a millennium and carries a warming potential over a hundred-year span of more than twenty-four thousand times that of carbon dioxide.

Molecular hydrogen, increasingly considered for energy storage and for cutting emissions in steelmaking and shipping, is not itself a greenhouse gas but can add to warming indirectly by changing atmospheric chemistry. Atmospheric hydrogen concentrations rose by 5.3 per cent between 2010 and 2024, the bulletin notes, and leaks from production, pipelines and storage could erode some of the climate benefit of hydrogen-based energy.

Full details of the findings are set out in the UN News report on the bulletin, and Reuters reported the same record figures from Geneva in its account of the release. The bulletin itself is based on measurements from the Global Atmosphere Watch network of monitoring stations.