The World Meteorological Organization (WMO) has published in its Greenhouse Gas Bulletin No. 22 that the global average surface concentration of CO2 reached a record 426.8 ppm in 2025, equal to 153% of the 1750 pre-industrial level (WMO press release, 27/10/2026). The increase of 2.8 ppm from 2024 was above the decadal average but below the 2023/2024 exceptional surge. The analysis used observations from 179 stations.
Methane (CH4) also reached a record 1,948 ppb, equal to 267% of the 1750 level, and nitrous oxide (N2O) a record 339.1 ppb. Long-lived greenhouse gas radiative forcing rose by 56% between 1990 and 2025 according to the NOAA index, with CO2 accounting for about 81% of the increase.
About half of annual CO2 emissions remain in the atmosphere, with the rest absorbed by land ecosystems and oceans. The strong 2023/2024 El Niño reduced biosphere carbon uptake, while 2025 saw a recovery of land carbon sinks and lower fire emissions. WMO expects CO2 concentrations to rise further in 2026, due to fossil fuel burning and a developing strong El Niño that will affect land sinks. Risks of reduced ocean CO2 uptake are also increasing.