The World Meteorological Organization (WMO) has issued a stark warning regarding the state of the global atmosphere, revealing that greenhouse gas concentrations have reached unprecedented levels. According to the agency's latest Greenhouse Gas Bulletin, the average global concentration of carbon dioxide (CO 2) reached 426.8 parts per million (ppm) last year, representing 153 per cent of the pre-industrial baseline from the year 1750.

WMO Deputy Secretary-General Ko Barrett emphasized the critical nature of these measurements, stating that every additional part per million traps additional heat, supercharging the ocean and the atmosphere. This phenomenon causes heat waves, tropical cyclones, and rainstorms to intensify faster than historical baselines prepared societies for.

Breaking Down the Baseline and Key Metrics

The upward trajectory of atmospheric warming is not solely driven by carbon dioxide. The levels of methane and nitrous oxide—the second and third most important long-lived greenhouse gases caused by human activities—also hit a new peak in 2025.

Greenhouse gases are trapping an unprecedented amount of heat in the atmosphere, providing energy for more extreme weather and associated risks to economies and societies. The past 11 years have been the warmest on record, and this trend is set to continue. Because CO 2 has a very long lifetime, it will affect the global climate not just for years, but for decades and even centuries.

When the Bulletin was first published in 2004, the annual average level of CO 2 measured by WMO's Global Atmosphere Watch network of monitoring stations was 377.5 ppm, compared with nearly 427 ppm today.

The El Niño Accelerator and Biosphere Feedback Loops

Growth rates of CO 2 have tripled since the 1960s, accelerating from an annual average increase of 0.8 ppm per year to 2.4 ppm per year in the decade from 2011 to 2020.

Tripling Growth Rates and Carbon Sink Pressures

An exceptional surge of 3.5 ppm during 2023-2024 coincided with a strong El Niño, which reduced the efficiency of the biosphere through more drought, drier vegetation, and more wildfires, according to WMO senior scientific officer Oksana Tarasova. Although the 2.8 ppm annual increase from 2024-2025 represented a more modest increase, it was nonetheless a substantial addition of carbon to the atmosphere from fossil fuel burning. The WMO expects to see a further increase in concentrations in 2026 because of fossil fuel burning and the development of a powerful El Niño, which will impact land carbon sinks as it did in 2023-2024.

Radiative Forcing and Long-Term Climate Trajectories

The agency's Bulletin reports on the amount of gas that accumulates in the atmosphere rather than new annual emissions. About half of the total CO 2 emitted each year remains in the atmosphere, while the rest is absorbed by Earth's land ecosystems and oceans.

The U.S. National Oceanic and Atmospheric Administration (NOAA) Annual Greenhouse Gas Index shows that from 1990 to 2025, the warming effect on our climate caused by greenhouse gases increased by 56 per cent, with CO 2 accounting for about 81 per cent of this increase, known as radiative forcing.

The Energy Transition Dilemma: Emerging Trace Gas Risks

As countries transform their energy systems towards decarbonization, the WMO noted that careful attention should be given to two potent but less abundant trace gases closely related to electricity production and distribution: molecular hydrogen (H 2) and sulphur hexafluoride (SF 6).

The Threat of Sulphur Hexafluoride (SF 6)

Widely used as a spark suppressant in electricity distribution, SF 6 use has risen steadily in the past three decades in line with increased global electrification. It has an atmospheric lifetime of over 1,000 years and has the highest 100-year global warming potential of approximately 24,300 times that of CO 2. The increase of SF 6 in 2025 was a record high.

Molecular Hydrogen (H 2) Leakage Concerns

Hydrogen concentration has increased by 5.3 per cent between 2010 and 2024. Hydrogen is being used as an energy storage medium for hard-to-decarbonize sectors such as:

  • Steelmaking
  • Shipping
  • Long-duration energy storage
  • Renewable sources
  • Transport applications

Its leakage into the atmosphere from production facilities, pipelines, storage tanks, and fuel cells poses a growing concern. Although hydrogen is not a greenhouse gas, it influences atmospheric chemistry and has a strong indirect effect on warming. Both H 2 leakage and SF 6 persistence represent potential threats that could undermine the climate benefits of the energy transition. Careful monitoring of the composition of Earth's atmosphere is essential to detect, understand, and prevent unintended consequences of these changes.

Implications for Global Climate Policy and COP31

WMO releases the Bulletin to provide authoritative scientific data for negotiators attending the annual UN Climate conference. The aim of the Conference of the Parties meeting (COP31) in Antalya, Türkiye, from 9 to 20 November is to turn climate commitments into concrete action.