Methane reached 267% and nitrous oxide 126% of pre-industrial levels
The World Meteorological Organization’s annual Greenhouse Gas Bulletin, announced Tuesday, reported that atmospheric carbon dioxide averaged 426.8 parts per million in 2025 — the highest annual concentration on record, and 153% of pre-industrial levels. The United Nations’ climate agency, based in Geneva, Switzerland, has tracked the gas since 2004, when it stood at 377.5 parts per million. The 2025 figure is a 13.06% increase on that level.
The change over the most recent year was smaller than the two-decade rise but still positive: the 2024 average was 423.9 parts per million, and the 2025 reading is 0.68% higher.
Carbon dioxide was not the only gas at a record. The WMO reported that methane reached 267% of pre-industrial levels and nitrous oxide reached 126%, with both gases also hitting new highs in 2025. The agency attributed carbon dioxide primarily to fossil fuel-related emissions, methane typically to agricultural and waste sources, and nitrous oxide to natural and man-made sources including oceans, soils and fertilizer use.
WMO Deputy Secretary-General Ko Barrett said each additional part per million of carbon dioxide added to the atmosphere traps additional heat. “In effect, we are supercharging the ocean and the atmosphere,” she told journalists in Geneva. “That means that heat waves, tropical cyclones and rainstorms are intensifying faster than our historical baselines prepared us for.”
Barrett tied the measurements to the recent temperature record. “The past 11 years have been the warmest on record and this trend is set to continue,” she said. “CO2 has a very long lifetime and so will affect the global climate not just for years but for decades and even centuries.”
The bulletin builds on a forecast the WMO issued in May, when the agency said it expects the average global temperature to remain at or near record highs over the next five years. The average surface temperature is expected to be between 1.3 degrees Celsius and 1.9 degrees Celsius above the global average temperature recorded between 1850 and 1990.
That five-year window also includes expectations of recurring El Niño conditions. The report expects El Niño at least twice in the next five years, a pattern that drives higher temperatures in the tropics.
The WMO also said a strong El Niño accelerates the growth rates of greenhouse gases in the atmosphere. That effect, the agency said, reduces “the efficiency of the biosphere through more drought, drier vegetation and more wildfires,” WMO senior scientific officer Oksana Tarasova said.
The report therefore pairs two different kinds of statement: measured concentrations for 2025 that the WMO published as records, and expectations for the five years ahead in which the agency anticipates temperatures at or near record highs and El Niño conditions at least twice.