Greenhouse gases in Earth’s atmosphere climbed to fresh record levels in 2025, the United Nations said, a jump that commits the planet to climate effects expected to endure for centuries.
Concentrations of the three dominant heat-trapping gases — carbon dioxide, methane and nitrous oxide — all reached unprecedented levels last year, according to the UN’s weather and climate agency.
The World Meteorological Organization (WMO) said the continued build-up of these gases would translate into additional long-term warming.
The findings are detailed in the WMO’s 22nd annual Greenhouse Gas Bulletin, released ahead of the COP31 UN climate summit in Antalya, Turkey, scheduled for 9-20 November.
“Another year, another new record,” WMO deputy secretary-general Ko Barrett said.
“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.”
El Niño effect
Rather than tallying yearly emissions from activities such as burning coal, oil and gas, the bulletin focuses on atmospheric concentrations — the amount of each gas lingering in the air.
The madrid skyline seen in the distance with smog in the air
In 2025, carbon dioxide concentrations measured 426.8 parts per million (ppm); methane reached 1,948 parts per billion, and nitrous oxide stood at 339.1 parts per billion.
Those readings put the three gases at 153%, 267% and 126% of pre-industrial levels recorded before 1750.
Carbon dioxide is responsible for about 66% of the warming impact from the three main greenhouse gases.
Roughly half of the CO2 released each year remains in the atmosphere, while the remainder is taken up by land and the oceans.
Between 2024 and 2025, the global average CO2 concentration increased by 2.8 ppm — slower than the record rise of 3.6 ppm from 2023 to 2024.
WMO senior scientific officer Oksana Tarasova attributed the smaller rise to the “recovery of the land carbon sinks and reduced fire carbon emissions in 2025 after the strong 2023/2024 El Nino”, referring to the naturally occurring warming pattern that can influence climate and ecosystems.
“However, a 2.8 ppm annual increase is still a substantial addition of carbon to the atmosphere from fossil fuel burning.”
The 2025 increase also exceeded the past decade’s average annual growth rate of 2.6 ppm — a benchmark that was 0.8 ppm in the 1960s.
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“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.
Growing concerns over H2, SF6
Methane contributes about 16% of the warming effect from long-lived greenhouse gases, even though it persists in the atmosphere for a far shorter time than CO2.
About one-third of methane entering the atmosphere comes from natural sources such as wetlands, with the remainder linked to human activities including cattle, rice cultivation, landfills and biomass burning.
The bulletin said that as countries retool their energy systems for decarbonisation, policymakers and industry should also watch two powerful but relatively scarce trace gases tied closely to electricity generation and delivery: molecular hydrogen (H2) and sulfur hexafluoride (SF6).
SF6, used mainly as a spark suppressant in electricity distribution, has shown a steady increase over the past 30 years.
The reason H2 concentrations have risen over the last decade remains unclear, the bulletin noted, even as hydrogen is increasingly being adopted as an energy storage medium.
