Greenhouse gases hit record highs as WMO warns warming locked in for centuries

The World Meteorological Organization has published a Greenhouse Gas Bulletin every year since 2004, when the first edition put the global average carbon dioxide concentration at 377.5 ppm. The 22nd edition, released in Geneva on 27 October 2026, extends that series from a much higher starting point and lands less than two weeks before governments meet for COP31 in Antalya, Turkiye, scheduled for 9 to 20 November 2026.

The bulletin tracks atmospheric concentrations rather than annual emissions, and the distinction shapes how its findings should be read. A concentration is the net outcome of what is released into the air and what land and oceans absorb. The WMO notes that roughly half of the carbon dioxide emitted each year stays in the atmosphere, while the remainder is taken up by vegetation, soils and seawater. The number therefore describes an accumulated stock, not a yearly flow, which is why one year of slower growth does not undo the build-up.

The baseline for the series is 1750, the reference used for the pre-industrial atmosphere. The measurements come from the WMO Global Atmosphere Watch network, whose observations date back to 1957. The 2025 values are the highest recorded since that programme began, and the report presents them as unprecedented in the instrumental record. Because carbon dioxide persists in the atmosphere for a very long time, the bulletin treats today's concentrations as a commitment that will outlast any single political cycle.

Publication is timed for the annual UN climate conference so that delegations arrive with current atmospheric data. This year's meeting follows a stretch in which the 1.5C limit has dominated debate and in which researchers have warned that current emissions point to far more warming. The bulletin itself does not model policy choices. It reports what the atmosphere already holds, and it leaves the interpretation to the governments that will gather in Antalya.

Key Facts

The World Meteorological Organization reported on October 27 that the globally averaged surface concentration of carbon dioxide reached 426.8 ppm in 2025, with an uncertainty of plus or minus 0.2 ppm. That is 153 percent of the 1750 level. The increase from 2024 was 2.8 ppm, below the anomalously large 3.6 ppm jump recorded between 2023 and 2024 but slightly above the 2.6 ppm average annual growth rate for 2016 to 2025. In the 1960s the annual rise was about 0.8 ppm, so the growth rate has roughly tripled over six decades.

AFP reported on October 27 that methane stood at 1,948 ppb, or 267 percent of the pre-industrial level, and nitrous oxide at 339.1 ppb, or 126 percent. Methane's annual rise was 6 ppb, below the 10 ppb average of the past decade, while nitrous oxide added 1.1 ppb, in line with its recent average. The WMO's figures carry small uncertainties of plus or minus 2 ppb for methane and plus or minus 0.1 ppb for nitrous oxide. All three gases are at their highest since Global Atmosphere Watch observations began in 1957.

Oksana Tarasova, a senior scientific officer at the WMO, attributed the smaller carbon dioxide increase to the recovery of land carbon sinks and reduced fire emissions in 2025, following the strong 2023/2024 El Nino. She cautioned that 2.8 ppm is still 'a substantial addition of carbon to the atmosphere from fossil fuel burning'. The WMO expects concentrations to climb again in 2026 because of continued fossil fuel combustion and a developing powerful El Nino that could once more weaken the land sink.

New Scientist reported on October 27 that the bulletin also flags two trace gases tied to electrification. Sulphur hexafluoride, used mainly as a spark suppressant in electricity distribution equipment, has a 100-year warming potential roughly 24,000 times that of carbon dioxide and an atmospheric lifetime of more than 1,000 years, and its 2025 annual increase was the largest on record. Molecular hydrogen is not a greenhouse gas, but it slows the breakdown of methane and therefore has an indirect warming effect; its concentration rose 5.3 percent between 2010 and 2024.

Seoul Economic Daily reported on October 27 that background concentrations in Korea ran above the global averages, with domestic carbon dioxide at 432.7 ppm, methane at 2,023 ppb and nitrous oxide at 340.6 ppb. The Korea Meteorological Administration derives those figures from stations at Anmyeondo, Gosan on Jeju and Ulleungdo, and it has run the WMO World Calibration Centre for sulphur hexafluoride since 2012, having monitored the gas since 2007. The Korean report put the previous year's carbon dioxide rise at 3.5 ppm, while the WMO bulletin itself states 3.6 ppm.

Analysis

The headline number invites a misleading reading. Carbon dioxide grew more slowly in 2025 than in 2024, but that slowing came from the natural side of the ledger, not from a decline in fossil fuel use. Recovering forests and soils absorbed more carbon, and fewer fires released less, after the El Nino years. What this really means is that the atmospheric trend is still being driven by accumulated fossil carbon, with the year to year wiggle supplied by the variable strength of land and ocean sinks. A smaller increase is not the same as a small increase.

Carbon dioxide accounts for about 66 percent of the warming effect from long-lived greenhouse gases, and methane for about 16 percent. Methane's 6 ppb rise is modest against its own history, but each part per billion sits on top of a concentration already at 267 percent of the pre-industrial level. Nitrous oxide, largely associated with agriculture, keeps climbing at its familiar pace. Because roughly half of each year's carbon dioxide output stays airborne, the stock keeps growing even when the flow momentarily slows.

The bigger picture here is that decarbonisation is beginning to generate atmospheric problems of its own. Sulphur hexafluoride and molecular hydrogen are both embedded in the shift to electrification, one as insulation in power transmission and the other as an energy carrier and storage medium. Leaks of either can partly offset the emissions cuts that the same equipment is meant to deliver. That does not argue against electrification, but it does argue for leak detection, inventory work and calibration standards keeping pace with deployment.

The WMO's own outlook points to a rebound. Tarasova expects concentrations to rise further in 2026 as fossil fuel burning continues and a powerful El Nino develops, echoing conditions that weakened land sinks in 2023 and 2024. If that happens, the 2025 slowdown will look like a pause inside a trend rather than a turning point. The bulletin's value lies in exactly that kind of framing: it separates the long, slow accumulation from the noisy yearly variation and shows how little the underlying direction has changed.

Why It Matters

AFP reported on October 27 that Ko Barrett, the WMO's Deputy Secretary-General, opened the launch with a blunt summary: 'Another year, another new record.' She said greenhouse gases are trapping an unprecedented amount of heat in the atmosphere, providing energy for more extreme weather and the associated risks to economies and societies. She also noted that the past 11 years have been the warmest on record and that carbon dioxide's long lifetime means the climate effects will persist for decades and centuries.

New Scientist reported on October 27 that the bulletin follows UN confirmation that the 1.5C target is due to be exceeded within the next few years, with current emissions putting the world on a path to 2.8C of warming by 2100. Concentrations, unlike emissions, cannot be recalled once released. A policy that stopped adding carbon tomorrow would still leave the atmosphere holding what has already accumulated, which is why the report describes the current record as locking in additional long-term warming.

For national meteorological services, the numbers also carry an operational message. Korea's experience shows how background stations and calibration centres translate a global average into local evidence, and how a gas such as sulphur hexafluoride can be tracked through the same infrastructure that supports emissions accounting. Countries that expand grids and hydrogen networks will need comparable monitoring if they are to show that the climate benefits of electrification are not being eroded by leaks.

Next Up

Attention now turns to COP31 in Antalya, Turkiye, from 9 to 20 November 2026, where the bulletin will serve as one of the scientific inputs to negotiations. The report explicitly asks for more attention to sulphur hexafluoride and molecular hydrogen as countries decarbonise, an argument that lands as grids and hydrogen projects expand. Delegations will also have to reconcile the 2025 numbers with the wider warning that warming is on course to overshoot 1.5C.

The next test arrives with the 2027 bulletin, which will show whether the expected El Nino rebound materialises and whether land sinks recover again. Until then, the 22nd edition stands as the reference point: carbon dioxide at 426.8 ppm, methane at 1,948 ppb and nitrous oxide at 339.1 ppb, all records, all measured, and all still rising at a pace close to the recent average.