Record levels of carbon dioxide will impact us for centuries, the UN weather agency says

The latest from the agency Greenhouse Gas Bulletin shows the average global concentration of CO₂ on 426.8 parts per million (ppm) last year, or 153 percent of the 1750 pre-industrial baseline.

“Every additional part per million is important because it traps additional heat. In effect, we are pumping up the oceans and atmosphere. This means that heat waves, tropical cyclones and rainstorms are increasing faster than previously thought.” WMO Deputy Secretary General Ko Barrett told reporters in Geneva.

Also worrying is that levels of methane and nitrous oxide – the second and third most important long-lived greenhouse gases caused by human activity – also reached new peaks in 2025.

“Another year, another new record. Greenhouse gases trap unprecedented amounts of heat in the atmosphere, providing energy for more extreme weather and the associated risks to our economy and society,” stressed Ms. Barrett.

“The last 11 years have been the hottest on record and this trend will continue₂ has such a long lifespan that it will influence the global climate not just for years but for decades and even centuries.”

When this Bulletin was first published in 2004, the average annual level of CO₂ measured by WMO’s Global Atmospheric Watch monitoring station network was 377.5 ppm, compared with nearly 427 ppm today.

El Niño Accelerator

CO growth rate₂ has tripled since the 1960s, rising from an average annual increase of 0.8 ppm per year to 2.4 ppm per year in the 2011 to 2020 decade.

Outstanding [3.5 ppm] spike” in 2023-2024 coincides with a strong El Niño “which reduces the efficiency of the biosphere through more drought, drier vegetation and more forest fires,” said WMO senior scientific officer Oksana Tarasova.

He noted that while the 2.8 ppm annual increase in 2024-2025 represents a smaller increase, it represents “a significant addition of carbon to the atmosphere due to fossil fuel burning. We could see further increases in concentrations in 2026 due to fossil fuel burning and the development of a strong El Niño that will impact terrestrial carbon sequestration as it did in 2023-2024.”

TOGETHER₂ tripled growth rate

The agency’s bulletins report the amount of gas accumulating in the atmosphere and not new annual emissions. About half of the total CO₂ what is emitted each year remains in the atmosphere and the remainder is absorbed by the earth’s land and ocean ecosystems.

The US National Oceanic and Atmospheric Administration’s (NOAA) Annual Greenhouse Gas Index shows that from 1990 to 2025, the warming impact on our climate caused by greenhouse gases increased by 56 percent, with CO₂ accounted for about 81 percent of this increase, known as “radiative force.”

Energy transformation problem

WMO notes that as countries shift their energy systems towards decarbonization, careful attention should be paid to two powerful but lesser trace gases that are closely linked to the production and distribution of electricity: molecular hydrogen (H₂) and sulfur hexafluoride (SF₆).

Widely used as a spark suppressant in electrical distribution, SF₆ Electricity use has continued to increase in the last three decades along with increasing global electrification. “It has an atmospheric age of more than 1,000 years and has the highest global warming potential in 100 years, which is around 24,300 times that of CO2.₂. Improved SF₆ by 2025 is a record high,” the agency report noted.

Hydrogen concentration has increased by 5.3 percent between 2010 and 2024. Hydrogen is used as an energy storage medium for sectors that are difficult to decarbonize such as steelmaking, shipping, and long-term energy storage, as well as for renewable sources and as an energy source for transportation.

“Its leaks into the atmosphere from production facilities, pipelines, storage tanks and fuel cells are causing increasing concern,” the WMO said, highlighting that although hydrogen is not a greenhouse gas, “it affects the chemistry of the atmosphere” and has a strong indirect effect on warming, the agency explained.

“Both H₂ leaks and SF₆ “This persistence represents a potential threat that could undermine the climate benefits of the energy transition,” the WMO said. “Careful monitoring of the composition of the Earth’s atmosphere is essential to detect, understand and prevent the unintended consequences of these changes.”.

WMO publishes Bulletins to provide official scientific data for negotiators attending the annual UN climate conference. The aim of the Conference of the Parties (COP31) meeting in Antalya, Türkiye, from 9 to 20 November was to turn climate commitments into concrete actions.