Greenhouse gas levels hit record highs in 2025, UN says

WMO bulletin finds carbon dioxide, methane and nitrous oxide all at unprecedented concentrations

By LineZotpaper AI staff

Published27 October 2026

Read Time3 min

Illustration: Greenhouse gas levels hit record highs in 2025, UN says

Concentrations of the three main greenhouse gases rose to record highs in 2025, locking in climate impacts that will persist for decades and centuries, the UN's weather and climate agency said. The World Meteorological Organization's 22nd annual Greenhouse Gas Bulletin found carbon dioxide at 426.8 parts per million, methane at 1,948 parts per billion and nitrous oxide at 339.1 parts per billion.

The WMO said the three gases now stand at 153%, 267% and 126% of their pre-industrial levels respectively. Carbon dioxide accounts for about 66% of the warming effect on the climate, and around half of all CO2 emitted each year remains in the atmosphere, with the rest absorbed by land and oceans.

"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 has a very long lifetime and so will affect the global climate not just for years but for decades and even centuries."

The global average CO2 concentration rose by 2.8 ppm from 2024 to 2025, smaller than the record surge of 3.6 ppm the previous year. 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 Nino". She added: "However, a 2.8 ppm annual increase is still a substantial addition of carbon to the atmosphere from fossil fuel burning."

The rise is above the average growth rate of 2.6 ppm over the past decade, which stood at 0.8 ppm in the 1960s. Tarasova warned of a further increase in concentrations in 2026 because of fossil fuel burning and the development of a powerful El Nino.

Methane accounts for about 16% of the warming effect from long-lived greenhouse gases and has a much shorter lifetime than CO2. Around a third comes from natural sources such as wetlands, with the rest from cattle, rice farming, landfills and biomass burning.

The bulletin also urged more attention to two potent trace gases tied to electricity production and distribution: sulfur hexafluoride (SF6), a spark suppressant that has risen steadily over three decades, and molecular hydrogen (H2), whose increased levels over the past decade remain unexplained as it gains use as an energy storage medium.

The report comes ahead of the COP31 UN climate summit in Antalya, Turkey, running from 9 to 20 November.

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Analysis

Why This Matters

Record concentrations of CO2, methane and nitrous oxide mean more long-term warming and greater risk of extreme weather and associated economic and social damage.
Because CO2 persists in the atmosphere for decades to centuries, the impacts of current levels are effectively locked in for generations.
The findings land just before COP31 in Antalya, Turkey, where countries will confront the gap between pledges and the atmospheric reality.

Background

The WMO is the UN's weather and climate agency. Its annual Greenhouse Gas Bulletin measures the concentration of gases already in the atmosphere, rather than new annual emissions, and this is its 22nd edition. The report tracks the three dominant long-lived greenhouse gases against levels before 1750, the conventional pre-industrial benchmark. The slowdown in CO2 growth in 2025 reflects natural variability, including the recovery of land carbon sinks and reduced fire emissions after the 2023/2024 El Nino, rather than a lasting shift in emissions trends.

What to Watch

Whether CO2 concentrations rise again in 2026, which Tarasova expects because of continued fossil fuel burning and a powerful El Nino affecting land carbon sinks.
The COP31 summit in Antalya, Turkey, from 9 to 20 November, and whether countries respond to the new figures with updated commitments.
How much attention H2 and SF6 receive as energy systems shift toward decarbonisation, given their rising concentrations and links to electricity infrastructure.

Sources

Greenhouse gas levels hit new record highs in 2025 - UN · RTÉ News

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12 claims in this story checked against 1 source: 12 supported.

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SupportedGreenhouse gas concentrations hit record highs in 2025, according to the UN.RTÉ News: “Greenhouse gas concentrations in the atmosphere rose to new record highs in 2025, locking in climate impacts that will persist for centuries to come, the United Nations has said.”
SupportedThe WMO bulletin found carbon dioxide, methane and nitrous oxide at unprecedented concentrations.RTÉ News: “Levels of the three main greenhouse gases - the climate-warming carbon dioxide, methane and nitrous oxide - all rose to unprecedented figures in 2025, the UN's weather and climate agency said.”
SupportedThe record concentrations lock in climate impacts that will persist for decades and centuries.RTÉ News: “Greenhouse gas concentrations in the atmosphere rose to new record highs in 2025, locking in climate impacts that will persist for centuries to come”
SupportedThe bulletin reported 2025 concentrations of 426.8 ppm for carbon dioxide, 1,948 ppb for methane and 339.1 ppb for nitrous oxide.RTÉ News: “In 2025, carbon dioxide concentrations were at 426.8 parts per million (ppm); methane at 1,948 parts per billion, and nitrous oxide at 339.1 parts per billion.”
SupportedThe gases stood at 153%, 267% and 126% of pre-industrial levels, respectively.RTÉ News: “That takes them respectively to 153%, 267% and 126% of the pre-industrial levels witnessed before the year 1750.”
SupportedKo Barrett said: “Another year, another new record,” and that greenhouse gases were trapping unprecedented heat and providing energy for extreme weather and associated risks.RTÉ News: “"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.”
SupportedCarbon dioxide accounts for about 66% of the warming effect on the climate.RTÉ News: “Of the three major greenhouse gases, CO2 accounts for about 66% of the warming effect on the climate.”
SupportedAround half of the CO2 emitted each year remains in the atmosphere, with the rest absorbed by land and oceans.RTÉ News: “Around half of the total CO2 emitted each year remains in the atmosphere; the rest is absorbed by the land and oceans.”
SupportedGlobal average CO2 concentration rose 2.8 ppm from 2024 to 2025, less than the 3.6 ppm rise from 2023 to 2024.RTÉ News: “From 2024 to 2025, the global average concentration of CO2 rose by 2.8 ppm - smaller than the record surge from 2023 to 2024 of 3.6 ppm.”
SupportedTarasova attributed the 2.8 ppm increase to recovering land carbon sinks and reduced fire emissions after the strong 2023/2024 El Niño.RTÉ News: “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"”
SupportedTarasova warned concentrations would increase further in 2026 because of fossil fuel burning and the development of a powerful El Niño.RTÉ News: “"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," Ms Tarasova warned.”
SupportedMethane accounts for about 16% of the warming effect from long-lived greenhouse gases.RTÉ News: “Methane accounts for about 16% of the warming effect on our climate by long-lived greenhouse gases”