Greenhouse Gases Reached New Highs in 2025, U.N. Agency Says
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The atmosphere keeps the books, and it has no rewind button: The three main greenhouse gases all reached record levels in 2025, and the climate will feel the consequences for centuries.
The World Meteorological Organization (WMO) announced the finding on Tuesday in its new Greenhouse Gas Bulletin. According to the U.N. weather and climate agency, concentrations of carbon dioxide, methane and nitrous oxide all stood at the highest levels since measurements began. The increase will lead to further long-term temperature rises on the planet, the agency said.
The Numbers at a Glance
The bulletin measures how much of each gas is in the atmosphere, not how much is newly emitted. The figures for 2025:
- Carbon dioxide: 426.8 parts per million (ppm), or 153 percent of the preindustrial level before 1750. When the bulletin began in 2004, the figure was 377.5 ppm.
- Methane: 1,948 parts per billion (ppb), or 267 percent of the preindustrial level.
- Nitrous oxide: 339.1 ppb, or 126 percent of the preindustrial level.
According to the radiative forcing index of the U.S. National Oceanic and Atmospheric Administration, the warming effect of all long-lived greenhouse gases rose 56 percent between 1990 and 2025. About 81 percent of that increase comes from CO2. Sulfur hexafluoride (SF6), an extremely long-lived gas that warms the planet about 24,300 times more strongly than CO2, also hit a record.
A Smaller Jump, a High Baseline
The concentration of CO2 rose by 2.8 ppm from 2024 to 2025. That is less than the record jump of more than 3.5 ppm the year before, but above the average of 2.6 ppm over the past decade. In the 1960s, the annual rise was just 0.8 ppm.
WMO scientist Oksana Tarasova attributes the smaller increase to the recovery of natural carbon sinks on land and to lower emissions from wildfires after the strong 2023-24 El Niño. About half of the CO2 emitted each year stays in the atmosphere, while land and oceans absorb the rest. “A 2.8 ppm annual increase is still a substantial addition of carbon to the atmosphere from fossil fuel burning,” Ms. Tarasova said.
Ko Barrett, the WMO’s deputy secretary general, put it this way: “Another year, another new record.” Greenhouse gases are trapping more heat in the atmosphere than ever, she said, providing energy for more extreme weather. Every additional part per million matters because it traps additional heat.
The WMO expects concentrations to rise further in 2026, driven by fossil fuel use and a developing El Niño. The current super El Niño has already set temperature records in the tropical Pacific. The WMO data also feed into negotiations at the COP31 climate summit in Antalya, Turkey, in November.
The Consequences Are Already Visible
Last summer showed what the warming means: According to two studies, heat killed more than 50,000 people in European cities, about two thirds of them because of climate change. And the U.N. Environment Programme’s Emissions Gap Report recently concluded that the 1.5-degree limit can no longer be held without overshooting it. Under current policies, the world is heading for 2.8 degrees.
China’s Emissions Are Flattening
Atmospheric concentrations lag behind emissions because CO2 stays in the air for decades to centuries. On the emissions side, there is a bright spot: According to an analysis in Carbon Brief, CO2 emissions in China, the largest emitter, have been flat or falling since March 2024. For 2025 as a whole, the author, Lauri Myllyvirta of the Centre for Research on Energy and Clean Air, estimates a decline of about 0.3 percent. Solar power generation rose 43 percent, wind 14 percent, and coal-fired generation fell 1.9 percent.
The analysis also lists caveats: Without growth in the chemicals industry, the decline would have been clearer, at about 2 percent. Emissions sit only slightly below their early-2024 peak, and a small rebound could push them back above it. Officially, China plans to peak emissions “before 2030.”
