Geneva — Concentrations of greenhouse gases in the atmosphere have reached record levels in 2025, locking in climate impacts that will persist for centuries, the United Nations said Tuesday.
Levels of the three main greenhouse gases – carbon dioxide, methane and nitrous oxide – have all reached unprecedented numbers in 2025, the UN weather and climate agency has said.
The World Meteorological Organization said the increase would lead to a longer-term rise in the planet’s temperature.
The 22nd Annual WMO Greenhouse Gas Bulletin comes ahead of the COP31 UN climate summit in Antalya, Turkey, from 9-20 November.
“Another year, another record,” said WMO Deputy Secretary-General Ko Barrett.
“Greenhouse gases trap an unprecedented amount of heat in the atmosphere, providing energy for more extreme weather and associated risks to our economies and societies.
“The last 11 years have been the warmest on record and this trend will continue. Carbon dioxide (CO2) is very long-lived and will therefore affect the global climate not just for years but for decades or even centuries.”
The impact of El Niño
The report card looks at greenhouse gas concentrations – the amount of these gases in the atmosphere – rather than new amounts of annual emissions as the world burns more coal, oil and gas.
In 2025, carbon dioxide concentrations were 426.8 parts per million (ppm); methane at 1,948 parts per billion and nitrous oxide at 339.1 parts per billion.
This brings them to 153%, 267% and 126% respectively of the pre-industrial levels observed before 1750.
Among the three main greenhouse gases, CO2 represents approximately 66% of the global warming effect.
About half of the total CO2 emitted each year remains in the atmosphere; the rest is absorbed by land and oceans.
From 2024 to 2025, the global average CO2 concentration increased by 2.8 ppm, less than the record increase from 2023 to 2024 of 3.6 ppm.
Oksana Tarasova, WMO senior science officer, said this reflected “the recovery of terrestrial carbon sinks and the reduction of fire carbon emissions in 2025 after the strong El Nino of 2023/2024”, the natural weather phenomenon that causes global warming.
“However, an annual increase of 2.8 ppm still represents a substantial addition of carbon to the atmosphere from the burning of fossil fuels.”
It is also higher than the average growth rate over the past decade of 2.6 ppm – a figure that was 0.8 ppm in the 1960s.
“We can expect a further increase in concentrations in 2026 due to the burning of fossil fuels and the development of a strong El Nino which will impact terrestrial carbon sinks, as was the case in 2023/2024,” Tarasova warned.
Methane is responsible for about 16% of the global warming effect of long-lived greenhouse gases, although its lifespan is much shorter than that of CO2.
About a third of the methane emitted into the atmosphere comes from natural sources such as wetlands, with the rest coming from anthropogenic sources such as livestock, rice farming, landfills and biomass burning.
The bulletin says that as countries shift their energy systems toward decarbonization, more attention should be paid to two powerful but less abundant trace gases closely linked to electricity generation and distribution: molecular hydrogen (H2) and sulfur hexafluoride (SF6).
SF6 has increased steadily over the past three decades. It is mainly used as a spark arrester in electricity distribution.
It’s unclear why hydrogen levels have increased over the past decade, but it has begun to be used as a means of energy storage.
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