Global concentrations of carbon dioxide (CO2), methane and nitrous oxide reached unprecedented levels in 2025, increasing the threat of extreme weather and putting economies and societies at greater risk, the World Meteorological Organization (WMO) has warned.
The agency’s latest Greenhouse Gas Bulletin found that the average global concentration of CO2 climbed to 426.8 parts per million (ppm) last year, equivalent to 153 per cent of the pre-industrial level recorded in 1750, reports UNB.
“Every additional part per million matters because it traps additional heat. In effect, we are supercharging the ocean and the atmosphere. That means that heat waves, tropical cyclones, and rainstorms are intensifying faster than our historical baselines prepared us for,” WMO Deputy Secretary-General Ko Barrett told journalists in Geneva.
Methane and nitrous oxide, the second and third most significant long-lived greenhouse gases produced by human activities, also reached record concentrations in 2025.
“Another year, another new record. Greenhouse gases are trapping an unprecedented amount of heat in the atmosphere, providing energy for more extreme weather and associated risks to our economies and societies,” Barrett said.
She said the past 11 years had been the warmest on record and that the trend was expected to continue. As CO2 stays in the atmosphere for extended periods, its impact on the global climate will continue for decades and even centuries.
When the WMO first released the bulletin in 2004, its Global Atmosphere Watch monitoring network recorded an annual average CO2 concentration of 377.5 ppm. The figure has since climbed to nearly 427 ppm.
El Niño accelerates CO2 growth
The rate at which CO2 accumulates in the atmosphere has tripled since the 1960s, increasing from an annual average of 0.8 ppm to 2.4 ppm per year during the decade from 2011 to 2020.
WMO senior scientific officer Oksana Tarasova said the exceptional increase of 3.5 ppm between 2023 and 2024 coincided with a strong El Niño event. The phenomenon reduced the biosphere’s ability to absorb carbon as droughts intensified, vegetation became drier and wildfires increased.
Although the annual increase eased to 2.8 ppm between 2024 and 2025, Tarasova described the rise as a substantial addition of carbon to the atmosphere from fossil fuel burning.
She warned that CO2 concentrations could increase further in 2026 as fossil fuel consumption continues and a powerful El Niño develops. Such conditions could weaken land-based carbon sinks, as they did in 2023-2024.
Greenhouse gases intensify global warming
The WMO bulletin tracks the accumulation of greenhouse gases in the atmosphere rather than emissions produced each year. About half of the CO2 emitted annually remains in the atmosphere, while land ecosystems and oceans absorb the rest.
The US National Oceanic and Atmospheric Administration’s Annual Greenhouse Gas Index shows that the warming influence of greenhouse gases on the climate increased by 56% between 1990 and 2025.
CO2 accounted for around 81% of that increase, known as radiative forcing.
Energy transition raises new concerns
As countries move towards cleaner energy systems, the WMO has called for close monitoring of two less abundant gases linked to electricity production and distribution: molecular hydrogen (H2) and sulphur hexafluoride (SF6).
SF6, which is widely used to prevent electrical sparks in power distribution systems, has seen its use rise steadily over the past three decades alongside growing global electrification.
The gas remains in the atmosphere for more than 1,000 years and has a 100-year global warming potential about 24,300 times greater than that of CO2. According to the bulletin, the increase in atmospheric SF6 in 2025 was the highest on record.
Meanwhile, atmospheric hydrogen concentrations rose by 5.3% between 2010 and 2024.
Hydrogen is increasingly used for energy storage and in industries that are difficult to decarbonise, including steelmaking and shipping. It also supports renewable energy systems, long-duration energy storage and transport.
However, hydrogen leakage from production facilities, pipelines, storage tanks and fuel cells is emerging as a growing concern.
Although hydrogen is not itself a greenhouse gas, it influences atmospheric chemistry and can indirectly contribute to global warming, the WMO said.
The agency warned that hydrogen leaks, combined with the long atmospheric lifetime of SF6, could undermine the climate benefits expected from the global transition to cleaner energy.
It stressed that continuous atmospheric monitoring is essential to identify, understand and prevent unintended consequences arising from changes in energy systems.
The WMO publishes the bulletin to provide authoritative scientific evidence for negotiators attending the annual United Nations climate conference.
The 31st Conference of the Parties (COP31), scheduled to take place in Antalya, Türkiye, from November 9 to 20, aims to turn climate commitments into concrete action.
