Greenhouse gas levels in the atmosphere reached unprecedented levels in 2025, which could cause even greater warming of the planet and lead to more extreme weather events, according to the World Meteorological Organization (WMO), a United Nations agency, in a report released on Tuesday.
The global average concentration of CO₂ in the atmosphere reached 426.8 parts per million in 2025, about 153% of the pre-industrial level of 1750, according to the report. The level rose by 2.8 ppm compared with the previous year, an annual increase greater than the average of the last decade.
Concentrations of other important greenhouse gases — methane and nitrous oxide — reached record levels in 2025, standing at 267% and 126% of pre-industrial levels, respectively. The report measures the amount of gas that accumulates in the atmosphere, and not the new annual emissions.
The WMO will share the conclusions with negotiators at the UN Climate Conference COP31, in Antalya, Turkey, in November, and warned that a strong El Niño could raise concentrations further this year.
“Each additional part per million is important because it traps extra heat. In practice, we are overloading the ocean and the atmosphere,” said Ko Barrett, the Deputy Secretary-General of the WMO.
“That means heat waves, tropical cyclones and storms are intensifying more quickly than our historical references prepared us to face.”
This year, regions around the world, including Europe, experienced scorching heat in the summer, in addition to devastating floods in Asia and elsewhere.
The WMO stated that it expects CO₂ concentrations to rise even further this year due to burning fossil fuels and the onset of a strong El Niño, which will cause drier conditions and make it more difficult for carbon sinks to absorb emissions.
The WMO also expressed concern about sulfur hexafluoride, or SF₆, a greenhouse gas widely used in electrical equipment, saying that its increase in 2025 reached a historic high. The global warming potential of SF₆ is more than 24,000 times that of CO₂, and it can remain in the atmosphere for more than 1,000 years.
