Levels of major greenhouse gases (GHGs) in the atmosphere rose to "unprecedented highs" in 2025, the World Meteorological Organisation (WMO) said today.
The WMO data refer to measured GHG concentrations, or the GHGs that accumulate, rather than new annual emissions. The high levels are "locking in more long-term temperature increase for the planet", the WMO said. Data from individual monitoring stations suggest that CO2 levels continue to rise this year, the organisation added.
The global average surface concentration of CO2 in 2025 was 426.8 parts per million (ppm), or 153pc of the 1750 pre-industrial baseline, the WMO found. The average methane concentration in 2025 was 1,948 parts per billion (ppb) and for nitrous oxide it was 339.1 ppb — 267pc and 126pc above 1750 levels, the WMO said.
Of long-lived GHGs, CO2 made the biggest contribution to the increase in global radiative forcing — the warming effect on the world's climate — from the pre-industrial era to 2025, at 66pc, WMO data show. Methane accounted for 16pc and nitrous oxide 6pc.
Growth rates in CO2 have trebled since the 1960s, increasing from an annual average rise of 0.8 ppm to 2.4 ppm in the decade from 2011-2020, the WMO said. The global average concentration of CO2 went up by 2.8 ppm in 2024-25, it added.
This is a "more modest" growth rate compared to the "exceptional surge" from 2023-24, the WMO said. It "reflects recovery of the land carbon sinks and reduced fire carbon emissions in 2025 after the strong 2023/2024 El Nino", WMO senior scientific officer Oksana Tarasova said.
Tarasova expects a further increase in CO2 concentrations in 2026, owed to "fossil fuel burning and the development of a powerful El Nino which will impact land carbon sinks", she said.
Of the CO2 emitted each year, around half remains in the atmosphere, while the rest is "absorbed by land ecosystems and oceans", the WMO said.
The Paris climate agreement seeks to curb the global rise in temperature to "well below" 2°C above pre-industrial levels — using an 1850-1900 baseline — and pursues a 1.5°C limit. Climate action is typically centred around mitigation, or cutting emissions, to avoid a further increase in temperature. The global increase in temperature since the pre-industrial era is 1.4°C, WMO data show, while an "overshoot" of the 1.5°C goal is likely in the next few years, the UN said in September.
