Atmospheric concentrations of the three primary greenhouse gases rose to record levels in 2025, according to a report released Tuesday by the World Meteorological Organization (WMO). The United Nations agency found that levels of carbon dioxide (CO2), methane, and nitrous oxide reached unprecedented figures, which the agency stated will sustain climate impacts for centuries. The WMO’s 22nd annual Greenhouse Gas Bulletin was published in advance of the COP31 climate summit scheduled for November 9–20 in Antalya, Turkey.
The report distinguishes between atmospheric concentrations—the amount of gas remaining in the air—and annual emission rates. While the global average concentration of CO2 rose by 2.8 parts per million (ppm) from 2024 to 2025, this increase was smaller than the 3.6 ppm surge recorded the previous year. WMO senior scientific officer Oksana Tarasova attributed this relative slowdown to the recovery of land carbon sinks and a reduction in fire emissions following the 2023–2024 El Niño weather phenomenon. However, the 2.8 ppm rise remains higher than the average growth rate of 2.6 ppm seen over the last decade.
In 2025, CO2 concentrations reached 426.8 ppm, methane rose to 1,948 parts per billion (ppb), and nitrous oxide reached 339.1 ppb. These figures represent 153%, 267%, and 126% of pre-industrial levels, respectively. Preliminary data for 2025 indicated greenhouse gas emissions increased in the United States, China, and Indonesia, while India, Russia, and the European Union saw declines. The United States recorded the largest increase among the reported countries and blocks, with emissions rising by an estimated 133 million tons of carbon dioxide equivalent.
To have a 50% chance of bringing global warming back down to 1.5°C by 2100, the UN reports that annual emissions would need to decrease by approximately 6% every year through 2035. Achieving this would require a rapid reduction in fossil fuel use alongside the large-scale removal of carbon dioxide from the atmosphere. The WMO also highlighted the rise of sulfur hexafluoride (SF6), used as a spark suppressant in electricity distribution, and molecular hydrogen (H2), an energy storage medium, as trace gases requiring closer monitoring as nations transition their energy systems toward decarbonization.
The report indicates that 2025 is set to be either the second or third warmest year on record, following a decade in which the past 11 years have been the warmest in recorded history. Scientists at the WMO warn that because CO2 has a long atmospheric life, the heat trapped by current record concentrations will continue to influence global temperatures for centuries. Furthermore, the WMO expects concentrations to rise again in 2026 due to continued fossil fuel burning and the development of a powerful El Niño event, which typically reduces the ability of land sinks to absorb carbon.
The next steps for international policy will occur during the COP31 summit in Antalya, Turkey, beginning November 9, 2025. National governments are expected to discuss adaptation strategies and finance, particularly for developing countries. Additionally, new climate pledges, known as nationally determined contributions, are due for submission ahead of the COP30 summit in Brazil in 2026. These submissions will determine the formal trajectory for global emissions reductions through the next decade.