The World Meteorological Organization (WMO) has warned that concentrations of carbon dioxide (CO₂) and other major greenhouse gases reached record highs in 2025, locking in further long-term global warming and intensifying risks from extreme weather.
The agency’s latest Greenhouse Gas Bulletin found that the global average concentration of CO₂ reached 426.8 parts per million (ppm) in 2025, equivalent to 153 per cent of pre-industrial levels recorded in 1750. Methane and nitrous oxide, the second and third most important long-lived greenhouse gases linked to human activities, also reached new peaks.
WMO Deputy Secretary-General Ko Barrett stated that rising concentrations are increasing the amount of heat trapped in the atmosphere, with consequences for communities, economies and ecosystems.
“Every additional part per million matters because it traps additional heat. In effect, we are supercharging the ocean and the atmosphere. That means that heat waves, tropical cyclones, and rainstorms are intensifying faster than our historical baselines prepared us for.”
Ko Barrett
According to WMO, the most recent data highlight the growing amount of greenhouse gases in the atmosphere and the long-term effects on the world’s climate.
When the agency first published its Greenhouse Gas Bulletin in 2004, the annual average CO₂ concentration measured by its Global Atmosphere Watch network stood at 377.5 ppm, compared with 426.8 ppm in 2025.
“Another year, another new record. 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.”
Ko Barrett
She warned that the warming trend will continue because CO₂ remains in the atmosphere for extended periods, affecting the climate for decades and centuries.
“The past 11 years have been the warmest on record and this trend is set to continue. CO₂ has a very long lifetime and so will affect the global climate not just for years but for decades and even centuries.”
Ko Barrett
Also, US National Oceanic and Atmospheric Administration’s Annual Greenhouse Gas Index found that the warming effect of greenhouse gases increased by 56 per cent between 1990 and 2025, with CO₂ accounting for approximately 81 per cent of that increase.
The bulletin measures greenhouse gases accumulating in the atmosphere rather than new annual emissions. Approximately half of the CO₂ emitted each year remains in the atmosphere, while the remainder is absorbed by land ecosystems and the oceans.
El Niño and Carbon Sinks Drive CO₂ Increases
The report also highlights the accelerating rate of CO₂ accumulation, with annual growth rates tripling since the 1960s.
Average annual increases rose from 0.8 ppm in the 1960s to 2.4 ppm during the decade from 2011 to 2020. An exceptional 3.5 ppm increase in 2023–2024 coincided with a strong El Niño, which reduced the capacity of natural carbon sinks to absorb CO₂ through drought, drier vegetation and increased wildfires.
WMO Senior Scientific Officer, Oksana Tarasova, the annual increase slowed to 2.8 ppm between 2024 and 2025 but still represented a substantial addition of carbon to the atmosphere from fossil fuel burning.
She warned that concentrations could rise further in 2026 because of continued fossil fuel use and the development of a powerful El Niño, which could affect land-based carbon sinks as it did in 2023–2024.
The findings highlight the combined influence of human emissions and changing natural conditions on atmospheric greenhouse gas concentrations.
Although land ecosystems and oceans absorb a substantial share of emitted CO₂, their capacity to limit atmospheric accumulation can weaken under adverse conditions, allowing more carbon to remain in the atmosphere.
Energy Transition Faces Risks From SF₆ and Hydrogen Leaks
WMO has also cautioned that countries transitioning towards cleaner energy systems must monitor less abundant gases associated with electricity infrastructure and emerging energy technologies.
The agency highlighted sulphur hexafluoride (SF₆), widely used as an electrical insulator and spark suppressant in electricity distribution, whose atmospheric concentration has risen steadily over the past three decades alongside global electrification.
SF₆ has an atmospheric lifetime exceeding 1,000 years and a 100-year global warming potential approximately 24,300 times that of CO₂. Its increase in 2025 was the highest on record, according to the bulletin.
The agency also raised concerns about rising atmospheric concentrations of molecular hydrogen (H₂), which increased by 5.3% between 2010 and 2024.
Hydrogen is being explored as an energy storage medium and as a potential option for hard-to-decarbonise sectors, including steelmaking, shipping and transport. However, leakage from production facilities, pipelines, storage tanks and fuel cells could undermine some of its climate benefits.
Whereas hydrogen is not itself a greenhouse gas, WMO explained that it influences atmospheric chemistry and can contribute indirectly to warming.
The bulletin provides scientific evidence to inform negotiations at the annual UN climate conference, with COP31 expected to focus on translating climate commitments into practical measures.
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