Greenhouse gases reach record highs in 2025, deepening the planet’s warming burden

WMO is drawing attention to sulphur hexafluoride, or SF6, a gas used mainly to prevent electrical arcing in electricity distribution equipment.

Atmospheric carbon dioxide and other major greenhouse gases reached record levels in 2025, adding to the heat trapped around Earth and committing the planet to further warming. The World Meteorological Organization's Greenhouse Gas Bulletin puts the globally averaged surface concentration of carbon dioxide at 426.8 parts per million, equivalent to 153% of its pre-industrial level in 1750. Methane and nitrous oxide also reached new highs, reinforcing concerns about the lasting effects of human activity on the climate.

WMO Deputy Secretary-General Ko Barrett said the growing concentration of greenhouse gases supplies more energy for extreme weather, increasing risks for communities and economies. The past 11 years have been the warmest on record, with the continuing buildup of heat-trapping gases expected to sustain that trend. Carbon dioxide remains in the climate system for centuries, meaning today's emissions carry consequences far beyond the year they enter the atmosphere.

The bulletin provides scientific information for climate negotiators preparing for COP31, scheduled for November 9–20, 2026, in Antalya, Türkiye. The conference is expected to focus on turning climate commitments into practical action as atmospheric measurements show the scale of the challenge. WMO's findings also highlight the need to monitor gases associated with expanding electricity networks and emerging hydrogen industries.

Carbon dioxide growth remains above the recent average

The bulletin measures greenhouse gas concentrations, which describe the amount accumulating in the atmosphere, rather than the new emissions released during a particular year. Around half of the carbon dioxide emitted annually stays in the atmosphere, with land ecosystems and oceans absorbing the remainder. Changes in these natural carbon sinks can influence how quickly atmospheric concentrations rise, alongside emissions from fossil fuels and other human activities.

Carbon dioxide growth rates have tripled since the 1960s, rising from an average of 0.8 parts per million annually to 2.4 parts per million during 2011–2020. Concentrations increased by 2.8 parts per million between 2024 and 2025, exceeding that decadal average but falling below the exceptional increase recorded between 2023 and 2024. The annual concentration stood at 377.5 parts per million when WMO first published the bulletin in 2004, showing how much carbon dioxide has accumulated since then.

WMO senior scientific officer Oksana Tarasova linked the slower increase in 2025 to recovering land carbon sinks and lower fire emissions following the strong 2023–2024 El Niño. That event brought drought, drier vegetation and more wildfires, weakening the biosphere's ability to absorb carbon dioxide and increasing the amount left in the atmosphere. Tarasova said continued fossil fuel burning and a developing powerful El Niño could push concentrations higher in 2026, with climate change also increasing the risk of reduced ocean uptake.

Methane and nitrous oxide add to the warming pressure

NOAA's Annual Greenhouse Gas Index shows that the warming effect of long-lived greenhouse gases increased by 56% between 1990 and 2025. Carbon dioxide accounted for about 81% of that increase, making it the largest contributor to the additional warming influence over that period. WMO's carbon dioxide analysis draws on observations from 179 monitoring stations, supporting its assessment of global concentrations and growth rates.

Methane reached a globally averaged concentration of 1,948 parts per billion in 2025, equivalent to 267% of its level in 1750. It contributes about 16% of the warming effect from long-lived greenhouse gases, despite spending considerably less time in the atmosphere than carbon dioxide. Around 35% of methane emissions come from natural sources such as wetlands, with the remaining 65% coming from activities including livestock farming, rice cultivation, fossil fuel extraction, landfills and biomass burning.

Nitrous oxide, the third most important long-lived greenhouse gas, reached a globally averaged concentration of 339.1 parts per billion in 2025. Its sources include natural processes and human activities such as fertilizer use, biomass burning and industrial production. The bulletin's breakdown of warming influence since the pre-industrial era assigns approximately 66% to carbon dioxide, 16% to methane, 6% to nitrous oxide, 8% to CFCs and 2% each to HCFCs and HFCs.

Clean energy expansion brings gases that need closer monitoring

WMO is drawing attention to sulphur hexafluoride, or SF6, a gas used mainly to prevent electrical arcing in electricity distribution equipment. Its concentration has risen alongside global electrification over the past three decades, with a record annual increase reported in 2025. SF6 persists in the atmosphere for more than 1,000 years and has a warming potential over 100 years approximately 24,300 times that of carbon dioxide.

Atmospheric hydrogen increased by 5.3% between 2010 and 2024, raising concerns about leakage as its use expands in steelmaking, shipping, transport and energy storage. Hydrogen does not directly act as a greenhouse gas, but it changes atmospheric chemistry in ways that can intensify warming. Leaks from production facilities, pipelines, storage tanks and fuel cells could erode some of the climate benefits expected from replacing fossil fuels.

The two gases present different challenges for the energy transition, from the persistent accumulation of SF6 to hydrogen's indirect effects on warming. WMO's Global Atmosphere Watch programme coordinates observations and supports internationally recognized measurement standards for both gases, helping researchers compare findings across monitoring networks. Consistent measurements are needed to track their sources and removal processes, identify unintended consequences and guide changes that protect the climate benefits of cleaner energy.