The World Meteorological Organization warns that El Niño could drive another surge in 2026 by weakening natural systems that absorb about half of human carbon dioxide emissions.
Atmospheric carbon dioxide reached a record high in 2025, although its annual increase was smaller than in 2024, the World Meteorological Organization (WMO) said. Yale Environment 360 covered the UN weather and climate agency’s findings and its warning of a further El Niño-driven rise on October 28.
In its October 23 statement on the Greenhouse Gas Bulletin, WMO put the global average surface concentration at 426.8 parts per million (ppm), a measure of carbon dioxide’s share of the air. The increase from 2024 was 2.8 ppm—above the decade’s average, but below the exceptional 2023–2024 rise. The analysis used observations from 179 stations.
Those figures measure carbon dioxide accumulated in the atmosphere, rather than newly released annual emissions. A smaller increase therefore still means that the amount in the air grew.
WMO senior scientific officer Oksana Tarasova attributed the slower 2025 increase to recovering land carbon sinks—ecosystems that absorb carbon dioxide—and reduced fire emissions. That recovery followed the strong 2023–2024 El Niño, which brought drought, drier vegetation and more wildfires, weakening the land’s ability to absorb the gas.
During El Niño, warm water pools in the eastern Pacific, contributing to warmer weather globally, heavier rain in some places and drought in others. Severe heat and drought reduce the carbon dioxide plants absorb, while soils release more into the atmosphere. Warmer oceans also absorb less.
Hotter, drier conditions also encourage wildfires and degrade wetlands and tundra, releasing more heat-trapping gases. Natural systems normally absorb about half of the carbon dioxide humans emit each year. During El Niño, those systems offset less of the continuing fossil-fuel emissions while releasing more emissions themselves.
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Ko Barrett, WMO’s deputy secretary-general, warned that the strong El Niño underway in 2026 sets the stage for another surge in carbon dioxide. In her October 27 statement, she said individual WMO monitoring stations already showed levels continuing to rise in 2026. Those station readings are distinct from the completed global annual assessment for 2025.
Forecasting the interaction between fossil-fuel emissions, warming and emissions from natural systems remains difficult, Yale Environment 360 said. Emissions from burning forests, melting tundra and fermenting wetlands are largely absent from influential climate models used in negotiations, it said, while scientists are working to fill those gaps.
Barrett said greenhouse gases are trapping an unprecedented amount of heat, providing energy for more extreme weather and associated risks to economies and societies. Carbon dioxide’s long lifetime means its climate effects persist for decades and even centuries.
WMO publishes the bulletin to inform climate negotiators. The next UN climate conference, COP31, is scheduled for November 9–20, 2026, in Antalya, Türkiye, where countries will seek to turn climate commitments into concrete action.
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