Published on: 2026-10-27
Source: United Nations – United Nations –
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27 October 2026 Climate and Environment
According to a new report by the World Meteorological Organization (WMO), in 2025, the concentration of carbon dioxide (CO2) and other greenhouse gases in the atmosphere reached unprecedented high levels, which will lead to a long-term increase in the planet’s temperature.
The WMO Greenhouse Gas Bulletin reports that the global average surface concentration of CO2 in 2025 was 426.8 parts per million (ppm), or 153 percent of the pre-industrial baseline level of 1750. The concentration of methane and nitrous oxide – the second and third most significant long-lived greenhouse gases related to human activity – has also reached record levels.
“Another year – another record. Greenhouse gases trap an unprecedented amount of heat in the atmosphere, leading to an increase in extreme weather events,” said WMO Deputy Secretary-General Ko Barrett.
“The last 11 years have been the warmest in the entire history of observations, and this trend is likely to continue. CO₂ remains in the atmosphere for a very long time, and therefore will affect the global climate not just for many years, but for decades and even centuries,” she added.
WMO issues the Greenhouse Gas Bulletin to provide authoritative scientific information to participants at the 31st UN Climate Change Conference (COP-31). The goal of the COP-31 meeting, which will take place in Antalya (Turkey) from November 9 to 20, is to translate climate commitments into concrete actions.
The rate of CO2 concentration growth has tripled
The Bulletin provides data on greenhouse gas concentrations, not on new annual emission volumes. About half of the total amount of carbon dioxide emitted annually remains in the atmosphere, while the rest is absorbed by terrestrial ecosystems and the Earth’s oceans.
When the Bulletin was first published in 2004, the average annual level of carbon dioxide was 377.5 parts per million.
The annual greenhouse gas content index, calculated by the US National Oceanic and Atmospheric Administration (NOAA), shows that from 1990 to 2025, the radiative forcing of long-lived greenhouse gases – the warming effect on the climate – increased by 56 percent, with CO2 accounting for about 81 percent of this increase.
Since the 1960s, the rate of growth of carbon dioxide emissions has tripled: over the decade from 2011 to 2020, the average annual increase accelerated from 0.8 parts per million to 2.4 parts per million per year. From 2024 to 2025, the global average CO2 concentration rose by 2.8 parts per million, which is higher than the decade average but slightly less than in 2023–2024.
“In 2026, we can expect a further increase in concentration due to the burning of fossil fuels and the development of a strong El Niño, which will affect terrestrial carbon sinks, as occurred in 2023–2024. The risks of reduced CO2 absorption by the ocean also increase in the context of a changing climate,” said WMO senior scientist Oksana Tarasova.
Methane and nitrous oxide
Methane accounts for about 16 percent of climate warming caused by long-lived greenhouse gases, but its “lifetime” in the atmosphere is significantly shorter than that of CO2. Approximately 35 percent of methane comes from natural sources (such as wetlands), which are also sensitive to climate change, and around 65 percent comes from anthropogenic sources: methane emissions are associated with activities such as raising cattle, rice cultivation, fossil fuel use, waste disposal, and biomass burning.
The average global methane concentration in 2025 was 1948 parts per billion (ppb), or 267 percent of the 1750 level.
Nitrous oxide is the third most significant long-lived greenhouse gas, which comes from both natural sources and human activities such as biomass burning, fertilizer use, and various industrial processes.
The globally averaged concentration of nitrous oxide reached 339.1 parts per billion in 2025, which is 126 percent higher than the 1750 level.
Transition to clean energy
The WMO Global Atmosphere Watch network monitors carbon dioxide, methane, nitrous oxide, and other long-lived gases.
As countries respond and take measures to transform their energy systems towards decarbonization, special attention should be paid to two powerful but less common minor gas impurities closely associated with the production and distribution of electricity: molecular hydrogen (H2) and sulfur hexafluoride (SF6).
Over the past three decades, the content of SF6 has steadily increased—proportionally to the expansion of electrification worldwide, since SF6 is mainly used as an arc-quenching agent in power distribution systems.
Its atmospheric lifetime is over 1000 years, and it has the highest 100-year global warming potential – approximately 24,300 times that of CO2. The increase in SF6 concentration in 2025 was record high.
From 2010 to 2024, the concentration of hydrogen increased by 5.3 percent. Hydrogen is used as an energy storage medium for sectors where it is difficult to reduce carbon emissions, such as metallurgy, maritime transport, and long-term energy storage systems, as well as a source of energy for renewable sources and the transportation sector.
Nevertheless, its leakage into the atmosphere from production facilities, pipelines, storage tanks, and fuel cells raises concern. Hydrogen is not a greenhouse gas, but it affects the chemical composition of the atmosphere and therefore has an indirect impact on warming.
WMO, within its Global Atmosphere Watch program, coordinates global observations of both gases and maintains a stable and internationally recognized calibration scale for measurements of SF6 and H2 concentrations in the atmosphere.
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