Another year, another record. Concentrations of carbon dioxide (CO₂) and other human-induced greenhouse gases in the atmosphere reached unprecedented highs in 2025, committing the planet to further long-term warming, according to the latest WMO Greenhouse Gas Bulletin.
Atmospheric concentrations of these gases continue to rise, driving changes in the global climate. The past 11 years have been the warmest on record, says the report by the World Meteorological Organization (WMO), which assesses greenhouse-gas levels through 2025.
Globally averaged surface concentrations of the three main long-lived greenhouse gases associated with human activities—carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O)—reached record highs in 2025. CO₂ concentrations stood at 426.8 parts per million (ppm), 53 per cent above pre-industrial levels in 1750. Methane and nitrous oxide, the second- and third-most important long-lived greenhouse gases associated with human activities, reached 1,948 parts per billion (ppb) and 339.1 ppb, respectively. These concentrations were 167 per cent and 26 per cent above pre-industrial levels.
The planet’s troublesome trio
The three main long-lived greenhouse gases are closely linked to human activities and interact strongly with the biosphere and oceans.
Greenhouse gases’ contribution to global warming
Contribution of the main long-lived greenhouse gases to the increase in global radiative forcing between pre-industrial times and 2025.
“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 Ko Barrett, WMO deputy secretary-general.
Greenhouse gases are trapping unprecedented amounts of heat in the atmosphere, providing energy for more extreme weather and increasing risks to economies and societies.
The WMO Greenhouse Gas Bulletin is one of the organisation’s flagship annual publications. It provides authoritative scientific information for negotiators at the UN climate conference. The 31st Conference of the Parties (COP31), scheduled to take place in Antalya, Türkiye, from November 9 to 20, aims to turn climate commitments into concrete action.
CO₂ growth rates have tripled
When the bulletin was first published in 2004, the annual average CO₂ concentration measured by the WMO’s Global Atmosphere Watch network of monitoring stations was 377.5 ppm, states the WMO press release.
Growth rates have tripled since the 1960s, rising from an annual average increase of 0.8 ppm to 2.4 ppm in the decade from 2011 to 2020.
The National Oceanic and Atmospheric Administration’s (NOAA) Annual Greenhouse Gas Index shows that radiative forcing— the warming effect on the climate—from long-lived greenhouse gases increased by 56 per cent between 1990 and 2025. CO₂ accounted for about 81 per cent of this increase.
There was, however, a modest slowdown in the annual increase in CO₂ concentrations. Between 2024 and 2025, the annual mean rose by 2.8 ppm, down from the record increase of 3.6 ppm between 2023 and 2024. The latest increase was nevertheless slightly above the average annual growth rate of 2.62 ppm over the preceding decade.
The bulletin attributes the more modest increase to a likely recovery in land carbon sinks and lower carbon emissions from fires in 2025, following the strong El Niño of 2023-24.
“However, a 2.8 ppm annual increase is still a substantial addition of carbon to the atmosphere from fossil fuel burning. We can expect to see a further increase in concentrations in 2026 because of fossil fuel burning and the development of a powerful El Niño which will impact land carbon sinks as it did in 2023/2024. The risks of reduced CO2 uptake by the ocean are also increasing in our changing climate,” said WMO senior scientific officer Oksana Tarasova.
Carbon dioxide: at 153% of pre-industrial level
Globally averaged CO₂ concentration (a) and its growth rate (b), 1984–2025
Methane and nitrous oxide
Methane accounts for about 16 per cent of the warming effect of long-lived greenhouse gases. Even though it has a much shorter atmospheric lifetime than CO₂, its concentration continues to rise.
Approximately 35 per cent of methane emissions come from natural sources, such as wetlands, while about 65 per cent originate from human activities, including cattle farming, rice cultivation, fossil-fuel extraction, landfills and biomass burning.
The average annual increase in atmospheric methane concentrations fell from about 12 ppb in the late 1980s to almost zero between 1999 and 2006. Since 2007, however, concentrations have risen continuously. In 2025, the globally averaged concentration reached 1,948 ppb, equivalent to 267 per cent of the pre-industrial level.
Unlike CO₂, methane emissions from human activities are not dominated by fossil fuels worldwide. Agriculture and waste are also major sources. Studies based on methane measurements from the WMO’s Global Atmosphere Watch network suggest that increased emissions from tropical wetlands and human activities in the northern hemisphere’s mid-latitudes are likely contributors to the sustained rise since 2007.
Methane: At 267% of pre-industrial level
Globally averaged CH4 concentration (a) and its growth rate (b), 1984 to 2025
Nitrous oxide: At 126% of pre-industrial level
Globally averaged N2O concentration (a) and its growth rate (b), 1984 to 2025
Nitrous oxide, the third-most important long-lived greenhouse gas, comes from both natural sources and human activities, including biomass burning, fertiliser use and industrial processes. It accounts for about 6 per cent of the radiative forcing from long-lived greenhouse gases.
The globally averaged concentration of N₂O reached 339.1 ppb in 2025, an increase of 1.1 ppb from the previous year. This was 126 per cent of the pre-industrial level.
A careful transition to clean energy
The bulletin also warns that countries must pay attention to two potent but less abundant gases associated with electricity production and distribution as they transform their energy systems and move towards decarbonisation: molecular hydrogen (H₂) and sulphur hexafluoride (SF₆).
SF₆ concentrations have risen steadily over the past three decades, alongside the expansion of global electrification. The gas is used in electrical equipment, particularly as an insulating medium and to control electrical arcing.
SF₆ has an atmospheric lifetime of more than 1,000 years and a 100-year global warming potential approximately 24,300 times that of CO₂. Its atmospheric concentration recorded a record increase in 2025.
Atmospheric hydrogen concentrations rose by 5.3 per cent between 2010 and 2024. “The reasons for the increase of H2 over the past decade are currently unknown, but H2 has begun to be used as an energy storage medium that has strong potential in intermittent carbon-free energy production modes such as solar and wind,” the bulletin states.
Hydrogen is also being explored and used as an energy carrier and storage medium in hard-to-decarbonise sectors, including steelmaking and shipping, as well as in transport and systems that store energy from renewable sources. Hydrogen leakage from production facilities, pipelines, storage tanks and fuel cells is a growing concern. Hydrogen is not itself a greenhouse gas, but it influences atmospheric chemistry and can indirectly contribute to warming.
Short-lived but worrying
Ozone-depleting chlorofluorocarbons (CFCs), regulated under the Montreal Protocol on Substances that Deplete the Ozone Layer, together with other halogenated gases, account for about 12% of radiative forcing from long-lived greenhouse gases. While concentrations of CFCs and most halons are declining, some hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), which are also potent greenhouse gases, continue to rise relatively rapidly.
Although the bulletin focuses primarily on long-lived greenhouse gases, shorter-lived tropospheric ozone, a ground-level pollutant, also exerts a radiative forcing comparable to that of halocarbons. Its short atmospheric lifetime results in substantial horizontal and vertical variability, making global averages difficult to characterise through monitoring networks of the kind used to measure long-lived gases.
Other pollutants, including carbon monoxide, nitrogen oxides and volatile organic compounds, are not generally classified as greenhouse gases but can have direct or indirect effects on radiative forcing. Aerosols, or suspended particles in the atmosphere, are also short-lived substances that alter the Earth’s radiation budget.