Atmospheric concentrations of carbon dioxide (CO2), methane and nitrous oxide reached unprecedented levels in 2025, increasing the long-term warming risks facing the planet, according to the World Meteorological Organisation (WMO).

The WMO Greenhouse Gas Bulletin reported that the global average concentration of CO2 reached 426.8 parts per million (ppm) in 2025, equivalent to 153 per cent of the pre-industrial level recorded in 1750. Concentrations of methane and nitrous oxide, the second and third most important long-lived greenhouse gases associated with human activities, also rose to record levels.

“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 life-time and so will affect the global climate not just for years but for decades and even centuries,” said WMO Deputy Secretary-General Ko Barrett.

The WMO publishes the annual bulletin to provide scientific evidence for policymakers and negotiators ahead of the United Nations climate conference. The next meeting, COP31, is scheduled to take place in Antalya, Türkiye, from 9 to 20 November 2026, with the aim of translating climate commitments into concrete action.

CO2 Growth Rates Accelerate

The report measures greenhouse gas concentrations accumulating in the atmosphere rather than annual emissions. Around half of the CO2 emitted each year remains in the atmosphere, while the rest is absorbed by land ecosystems and oceans.

When the bulletin was first published in 2004, the annual average CO2 concentration measured by the WMO’s Global Atmosphere Watch monitoring network stood at 377.5 ppm.

Data from the US National Oceanic and Atmospheric Administration’s (NOAA) Annual Greenhouse Gas Index show that the warming effect of long-lived greenhouse gases increased by 56 per cent between 1990 and 2025, with CO2 accounting for approximately 81 per cent of that increase.

CO2 growth rates have tripled since the 1960s, rising from an annual average of 0.8 ppm to 2.4 ppm per year during the decade from 2011 to 2020.

Between 2024 and 2025, the global average CO2 concentration increased by 2.8 ppm. Although this was slightly below the exceptional rise recorded between 2023 and 2024, it remained above the average growth rate of the preceding decade.

WMO senior scientific officer Oksana Tarasova attributed the more moderate increase partly to the recovery of land carbon sinks and lower carbon emissions from wildfires in 2025 following the strong 2023-2024 El Niño event.

The earlier El Niño contributed to drought, drier vegetation and more wildfires, reducing the ability of the biosphere to absorb carbon.

“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 Tarasova.

Methane and Nitrous Oxide Reach New Records

Methane accounted for approximately 16 per cent of the warming effect caused by long-lived greenhouse gases. Although it remains in the atmosphere for a shorter period than CO2, it is a significant contributor to global warming.

The global average methane concentration reached 1,948 parts per billion (ppb) in 2025, equivalent to 267 per cent of its pre-industrial level.

Around 35 per cent of methane emissions originate from natural sources, including wetlands, which are themselves sensitive to climate conditions. The remaining 65 per cent comes from human activities such as livestock farming, rice cultivation, fossil fuel extraction, landfills and biomass burning.

Nitrous oxide concentrations also reached a record 339.1 ppb in 2025, standing 126 per cent above the 1750 level. Sources include natural processes and human activities such as fertiliser use, biomass burning and industrial production.

Energy Transition Brings Additional Climate Considerations

The WMO also highlighted the importance of monitoring molecular hydrogen (H2) and sulphur hexafluoride (SF6), two gases associated with electricity production, distribution and the transition to cleaner energy systems.

SF6 is widely used as an electrical insulating and arc-quenching gas in power distribution equipment. Its atmospheric concentration has increased steadily over the past three decades alongside global electrification, with the increase in 2025 reaching a record high.

The gas has an atmospheric lifetime exceeding 1,000 years and a 100-year global warming potential approximately 24,300 times that of CO2. Its persistence means emissions can contribute to warming for many centuries.

Hydrogen, meanwhile, is being developed as an energy carrier for sectors that are difficult to decarbonise, including steelmaking, shipping, transport and long-duration energy storage. However, atmospheric hydrogen concentrations increased by 5.3 per cent between 2010 and 2024.

Although hydrogen is not itself a greenhouse gas, leakage from production facilities, pipelines, storage tanks and fuel cells can affect atmospheric chemistry and contribute indirectly to warming.

The WMO warned that unmanaged hydrogen leakage and continued SF6 emissions could undermine some of the climate benefits expected from the energy transition.

Monitoring Essential to Climate Action

Through its Global Atmosphere Watch programme, the WMO coordinates international monitoring of CO2, methane, nitrous oxide, SF6, hydrogen and other atmospheric gases. The programme supports consistent measurement standards, enabling researchers to track concentration changes and investigate the sources and sinks of emissions.

The findings highlight the importance of reducing greenhouse gas emissions while monitoring the wider atmospheric effects of changing energy systems. The WMO said reliable global observations remain essential to understanding climate risks and ensuring that efforts to decarbonise economies deliver their intended environmental benefits. -OGN/TradeArabia News Service