GENEVA: Greenhouse gas concentrations in the atmosphere rose to record highs in 2025, locking in climate impacts that will persist for centuries, the United Nations said on Tuesday.
Levels of the three main greenhouse gases — carbon dioxide, methane and nitrous oxide — all reached unprecedented levels in 2025, the UN’s weather and climate agency said.
The World Meteorological Organization (WMO) said the rise would lead to further long-term increases in global temperatures.
The WMO’s 22nd annual Greenhouse Gas Bulletin comes ahead of the COP31 UN climate summit in Antalya, Turkey, which runs from Nov 9 to 20.
“Another year, another new record,” said WMO Deputy Secretary-General Ko Barrett.
“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. Carbon dioxide (CO2) has a very long lifetime and so will affect the global climate not just for years but for decades and even centuries.”
El Niño effect
The bulletin examines greenhouse gas concentrations — the amount of these gases in the atmosphere — rather than annual emissions, which continue as the world burns coal, oil and gas.
In 2025, carbon dioxide concentrations reached 426.8 parts per million (ppm), methane stood at 1,948 parts per billion, and nitrous oxide at 339.1 parts per billion.
These levels represent 153 per cent, 267 per cent and 126 per cent, respectively, of pre-industrial levels recorded before 1750.
Of the three main greenhouse gases, CO2 accounts for about 66 per cent of the warming effect on the climate.
Around half of the CO2 emitted each year remains in the atmosphere, while the rest is absorbed by land and oceans.
From 2024 to 2025, the global average concentration of CO2 rose by 2.8 ppm, below the record increase of 3.6 ppm recorded between 2023 and 2024.
WMO senior scientific officer Oksana Tarasova said this reflected the “recovery of the land carbon sinks and reduced fire carbon emissions in 2025 after the strong 2023/2024 El Niño”, the naturally occurring climate-warming phenomenon.
“However, a 2.8 ppm annual increase is still a substantial addition of carbon to the atmosphere from fossil fuel burning,” she said.
The increase also exceeded the average annual growth rate of 2.6 ppm over the past decade. In the 1960s, the figure stood at 0.8 ppm.
“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,” Tarasova warned.
Growing concerns over H2, SF6
Methane accounts for about 16 per cent of the warming effect caused by long-lived greenhouse gases, although it remains in the atmosphere for a much shorter time than CO2.
Around a third of methane emissions come from natural sources such as wetlands, while the rest originate from human activities, including cattle farming, rice cultivation, landfills and biomass burning.
The bulletin said that as countries shift towards decarbonising their energy systems, greater attention should be paid to two potent but less abundant trace gases closely linked to electricity production and distribution: molecular hydrogen (H2) and sulphur hexafluoride (SF6).
SF6, which is used primarily as an electrical insulator and arc suppressant in electricity distribution equipment, has been rising steadily over the past three decades.
The reasons for the increase in H2 levels over the past decade remain unclear, although the gas has begun to be used as an energy storage medium.
