The World Meteorological Organization (WMO) reported yesterday that atmospheric levels of carbon dioxide, methane, and nitrous oxide all reached record highs in 2025. In its annual Greenhouse Gas Bulletin, WMO reports that globally averaged surface concentrations of carbon dioxide reached 426.8 parts per million in 2025, or 153% of the pre-industrial baseline. Methane reached 1,948 parts per billion (ppb) and nitrous oxide 339.1 ppb.

CIRES scientists play a leading role in maintaining the data behind this flagship report. CIRES Research Scientist Xin (Lindsay) Lan chairs the Scientific Advisory Group on Greenhouse Gases for WMO’s Global Atmosphere Watch program, which produces the bulletin each year. CIRES scientist Andrew Crotwell also serves on the group. WMO releases the bulletin to provide scientific information for negotiators at the United Nations climate conference COP31 and the public.

“The bulletin reports on what’s accumulating in the atmosphere, so it all comes down to measurement quality,” Lan said. “By collecting and analyzing air samples worldwide and maintaining the calibration standards that put everyone’s data on the same scale, we can accurately detect year-to-year increases of a few parts per million or parts per billion that further enhance global radiative energy, which fuels more extreme weather.”

WMO notes that carbon dioxide growth rates have tripled since the 1960s. Because carbon dioxide stays in the atmosphere so long, today’s levels commit the planet to warming for decades to centuries. The past 11 years have been the warmest since the modern measurement record started. The report also flags sulfur hexafluoride and hydrogen as gases to watch as countries implement decarbonization strategies.

“Precise, long-term measurements let us see how today’s choices shape tomorrow’s climate,” Lan said.