Global carbon dioxide levels reach 426.8 parts per million as methane and nitrous oxide also set records, adding to long-term warming risks ahead of COP31.
By Bunmi Yekini
Greenhouse gas concentrations in the atmosphere reached record highs in 2025, locking in further global warming and increasing the risks of extreme weather, the World Meteorological Organization (WMO) said in a report released on Wednesday.
The WMO’s annual Greenhouse Gas Bulletin found that the global average concentration of carbon dioxide (CO2), the main driver of human-induced climate change, rose to 426.8 parts per million in 2025, equivalent to 153% of its pre-industrial level in 1750.
Methane and nitrous oxide, the second and third most important long-lived greenhouse gases linked to human activities, also reached record concentrations, the report 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,” WMO Deputy Secretary-General Ko Barrett said.
The past 11 years have been the warmest on record, Barrett said, adding that carbon dioxide would continue to affect the climate for decades and even centuries because of its long atmospheric lifetime.
The findings come ahead of the United Nations climate conference, COP31, scheduled to take place in Antalya, Türkiye, from November 9 to 20, where countries are expected to pursue concrete action on their climate commitments.
The report measures the concentration of greenhouse gases accumulating in the atmosphere, rather than the volume of emissions released each year. About half of the carbon dioxide emitted annually remains in the atmosphere, while the rest is absorbed by land ecosystems and the oceans.
CO2 growth rate triples
The annual rate of increase in atmospheric carbon dioxide has tripled since the 1960s, rising from an average of 0.8 parts per million a year to 2.4 parts per million in the decade from 2011 to 2020.
Between 2024 and 2025, the global average concentration increased by 2.8 parts per million, above the average for the previous decade, although slightly below the exceptional rise recorded between 2023 and 2024.
WMO attributed the more moderate increase partly to the recovery of land-based carbon sinks and a reduction in carbon emissions from fires in 2025, following the strong El Niño climate pattern of 2023 and 2024.
That El Niño contributed to drought, drier vegetation and more wildfires, reducing the ability of the biosphere to absorb carbon dioxide, said Oksana Tarasova, a senior scientific officer at the WMO.
However, the 2025 increase still represented a substantial addition of carbon to the atmosphere, largely from fossil fuel burning, Tarasova said.
She warned that concentrations could rise further in 2026 as fossil fuel use continues and a developing El Niño potentially reduces the capacity of land ecosystems to absorb carbon dioxide. Climate change could also weaken the oceans’ ability to take up the gas, she added.
The U.S. National Oceanic and Atmospheric Administration’s Annual Greenhouse Gas Index shows that the warming effect of long-lived greenhouse gases increased by 56% between 1990 and 2025, with carbon dioxide accounting for about 81% of that increase.
Methane, nitrous oxide also rise
Atmospheric methane concentrations averaged 1,948 parts per billion in 2025, equivalent to 267% of the pre-industrial level, the report said.
Methane accounts for about 16% of the warming effect of long-lived greenhouse gases. Around 65% of methane emissions come from human activities, including livestock farming, rice cultivation, fossil fuel extraction, landfills and biomass burning, while the remainder comes from natural sources such as wetlands.
Nitrous oxide concentrations reached 339.1 parts per billion in 2025, about 26% above the pre-industrial level. Sources include natural processes, fertiliser use, biomass burning and industrial activities.
The WMO also highlighted the need to monitor gases associated with electricity generation and distribution as countries shift towards cleaner energy systems.
Sulphur hexafluoride (SF6), used mainly in electrical equipment to prevent electrical discharges, has an atmospheric lifetime of more than 1,000 years. Its global warming potential over 100 years is about 24,300 times that of carbon dioxide, and its concentration recorded a record increase in 2025.
Hydrogen, although not itself a greenhouse gas, can indirectly contribute to warming by influencing atmospheric chemistry. Its concentration increased by 5.3% between 2010 and 2024, raising concerns about leaks from production facilities, pipelines, storage tanks and fuel cells.
The WMO said monitoring both gases would help scientists assess whether emissions and leaks from energy infrastructure could undermine some of the climate benefits expected from the transition to cleaner energy.
The organisation’s Global Atmosphere Watch programme coordinates international monitoring of greenhouse gases and other atmospheric constituents, providing data to help scientists track changes in the atmosphere and support climate policy decisions.