What happened
The World Meteorological Organization has reported a global mean atmospheric carbon dioxide concentration of 426.8 parts per million in 2025. The level was 2.8 ppm above 2024 and roughly 153% of the estimated pre-industrial concentration around 1750.
The agency also recorded peak 2025 concentrations for methane and nitrous oxide. These were equivalent to 267% and 126%, respectively, of their pre-industrial levels. Its assessment concerns gases already accumulated in the atmosphere, rather than the volume of emissions generated in one year.
WMO additionally drew attention to a record annual increase in sulphur hexafluoride, or SF6, which is used in electrical equipment. It said the gas has a warming potential exceeding 24,000 times that of CO2 and may persist in the atmosphere for more than 1,000 years.
Why it matters
Rising greenhouse-gas concentrations add to heat retained in the climate system. WMO linked that additional heat to faster intensification of heatwaves, tropical cyclones and heavy rainfall. The report follows severe summer heat in regions including Europe and damaging flooding in parts of Asia and elsewhere.
For organisations planning low-carbon infrastructure, the findings also underline the importance of managing non-CO2 climate risks. WMO noted that hydrogen is not a greenhouse gas directly, but leaks from its production, transport and storage systems can alter atmospheric chemistry and contribute indirectly to warming. It said such leakage, together with the exceptionally long lifetime of SF6, could diminish part of the climate benefit expected from the energy transition.
What to watch next
WMO expects CO2 concentrations to continue increasing while fossil-fuel use continues and drier conditions constrain the ability of carbon sinks to take up emissions. A strong El Niño could add further upward pressure, it said.
The organisation plans to present the findings to negotiators at the COP31 United Nations climate conference in Antalya in November. Companies with electrical assets or emerging hydrogen networks can use the report as a prompt to examine SF6 management and hydrogen-leakage controls alongside their direct-emissions plans.
