1576. Globally averaged concentrations of major greenhouse gases reach new record highs in 2025

On 27 October 2026, the World Meteorological Organization (WMO) published Greenhouse Gas Bulletin No. 22 and announced that globally averaged atmospheric concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) all reached new record highs in 2025. CO₂ reached 426.8 ppm, CH₄ reached 1,948 ppb and N₂O reached 339.1 ppb, corresponding to 153%, 267% and 126%, respectively, of their pre-industrial levels in 1750. The units ppm and ppb denote parts per million and parts per billion, respectively.

The following sections introduce the characteristics of each gas and the latest observations, drawing on the WMO Bulletin and related sources. The concentrations presented here describe the proportion of each gas in the atmosphere and are distinct from annual emissions.

Carbon dioxide: Up 2.8 ppm from the previous year

CO₂ is the largest contributor to the warming effect of long-lived greenhouse gases, accounting for about 66%. Its main anthropogenic source is the burning of fossil fuels such as coal, oil and natural gas. Cement production and land-use change, including deforestation, are also sources of emissions. According to the WMO Bulletin, its globally averaged concentration reached 426.8±0.2 ppm in 2025, up 2.8 ppm from the previous year. WMO explains that, because CO₂ remains in the atmosphere for a long time, current emissions will influence the climate for decades to centuries.

Methane: Emissions from both natural and anthropogenic sourcesCH₄ accounts for about 16% of the warming effect of long-lived greenhouse gases. According to WMO, approximately 35% of methane emissions come from natural sources such as wetlands, while about 65% are anthropogenic. In agriculture, livestock and rice cultivation are major sources; fossil-fuel extraction and use, waste disposal in landfills, and biomass burning also contribute. Its globally averaged concentration reached 1,948±2 ppb in 2025, up 6 ppb from the previous year. For the anomaly in methane stable carbon isotope ratios observed from mid-2023 to the end of 2024, the WMO Bulletin identifies increased emissions from biomass burning associated with major wildfires in North America and the Amazon, together with a small reduction in wetland emissions in regions experiencing hot and dry conditions, as the most likely cause. However, the Bulletin presents a tentative view of the changes in methane sources that may have caused this anomaly and describes the reduction in wetland emissions as a change in the regions affected by hot and dry conditions during 2023–2024.

Nitrous oxide: Human activities, including fertilizer use, also contribute to emissionsN₂O accounts for about 6% of the warming effect of long-lived greenhouse gases, making it the third-largest contributor after CO₂ and CH₄. It is released naturally from oceans and soils and is also emitted through human activities, with nitrogen fertilizer additions to croplands being the main anthropogenic source. According to the WMO Bulletin, global anthropogenic N₂O emissions increased by 30% over the past four decades, mainly driving the rise in its atmospheric concentration. Its globally averaged concentration reached 339.1±0.1 ppb in 2025, up 1.1 ppb from the previous year.

Related JIRCAS research initiativesJIRCAS also conducts research in fields related to the WMO report discussed above. Working with partner institutions in Asia and Africa, JIRCAS pursues research on reducing methane emissions from rice paddies, addressing biomass-related challenges, and improving nitrogen-use efficiency through biological mechanisms, with the aim of combining sustainable increases in food production with reductions in greenhouse gas emissions.

References:
World Meteorological Organization (2026), Greenhouse gas levels once again reach record high, 27 October 2026.
World Meteorological Organization (2026), WMO Greenhouse Gas Bulletin No. 22: The State of Greenhouse Gases in the Atmosphere Based on Global Observations through 2025, 27 October 2026.

Contributor: Miyuki IIYAMA, Strategic Coordination Office