Greenhouse gas concentrations hit record high in 2025, WMO says

Atmospheric concentrations of carbon dioxide, methane, and nitrous oxide reached record highs in 2025, according to the World Meteorological Organization's new Greenhouse Gas Bulletin. The organization warns that the buildup of these gases traps more heat and that carbon dioxide affects the climate for decades or even centuries.

The global average surface concentration of CO2 in 2025 was 426.8 parts per million, equal to 153 percent of the pre-industrial reference level from 1750. When the bulletin was first published in 2004, the annual average CO2 level was 377.5 ppm.

“Another year, another record.”

Between 1990 and 2025, the warming effect of long-lived greenhouse gases increased by 56 percent, according to the U.S. National Oceanic and Atmospheric Administration's Annual Greenhouse Gas Index. Carbon dioxide accounted for about 81 percent of that increase.

CO2 growth rates have tripled since the 1960s, rising from 0.8 ppm per year in 2011 to 2.4 ppm per year in 2020. From 2024 to 2025, average concentration rose by 2.8 ppm, exceeding the ten-year average. A further increase is expected in 2026 due to an intense El Niño, and the ocean may absorb less CO2.

Methane and nitrous oxide, the second and third most important long-lived greenhouse gases linked to human activity, also reached new records last year. Global average methane concentration in 2025 was 1,948 parts per billion, or 267 percent of the 1750 level. Nitrous oxide concentration reached 339.1 parts per billion.

The bulletin provides scientific information for negotiators at the United Nations Climate Change Conference, COP31, scheduled for November 9 to 20 in Antalya, Turkey.