The concentration of carbon dioxide (CO2) in Earth's atmosphere has reached a new record. In 2025, levels climbed to 426.8 parts per million: a level never previously recorded. That is 153 per cent above pre-industrial levels — that is, before humanity began burning coal, oil and gas to power its industries. The figure comes from the World Meteorological Organization (WMO), in the latest edition of its Greenhouse Gas Bulletin.

What is cause for concern, however, is not CO2 alone: similar records have also been registered for concentrations of methane and nitrous oxide — the second and third most prevalent greenhouse gases in the atmosphere around our planet, both driven by human activities.

"The effects of CO2 will persist for decades, if not centuries"

"A new year brings a new record. Greenhouse gases are trapping an unprecedented amount of heat, fuelling the intensification of extreme weather events and the resulting risks for our economies and our societies," commented Jo Barrett, WMO Deputy Secretary-General. She went on to remind us: "The last eleven years have been the warmest ever observed and the trend is set to continue. CO2 has a very long lifetime and therefore has an impact on the global climate for decades, if not centuries."

The data arrives just weeks before the opening of the thirty-first United Nations climate conference, Cop31, which will be held from 9 to 20 November in Antalya, Turkey. The hope is that governments will use the occasion to provide a concrete push to the process of mitigating climate change, starting with the transition from fossil fuels to renewable energy.

In 2004 we were at "only" 377.5 parts per million of CO2

The WMO Bulletin notes that the figure of 426.8 parts per million refers to the cumulative emissions accumulated in the atmosphere over time, not to annual emissions. Of the latter, roughly half is absorbed by terrestrial ecosystems and the oceans. The first report published, back in 2004, recorded "only" 377.5 parts per million — a reminder of the sharp acceleration in concentrations over recent decades. Overall, the figure represents a 53 per cent increase compared to pre-industrial levels.

Meanwhile, according to NOAA (the National Oceanic and Atmospheric Administration), between 1990 and 2025 the radiative forcing — that is, the climate-warming effect induced by the presence of greenhouse gases — grew by 56 per cent. And CO2 is responsible for 81 per cent of that increase.

Methane and nitrous oxide concentrations also at record levels

Furthermore, since the 1960s, annual accumulation has risen from 0.8 parts per million to 2.4 parts per million in the decade 2011–2020. In 2024 and 2025, the figure reached 2.8 parts per million. "We can expect a further increase in 2026, due to the continued use of fossil fuels and the presence of a strong El Niño, which could affect the oceans' capacity to absorb CO2," noted Oksana Tarasova, a WMO scientist.

As mentioned, alongside carbon dioxide, concentrations of methane have also risen — a gas that remains in the atmosphere for a shorter period but has a climate-altering potency dozens of times greater than CO2. In 2025, the figure reached 1,948 parts per billion, representing a 267 per cent increase over pre-industrial levels. Similarly, the quantity of nitrous oxide grew by 126 per cent over the same period, reaching 339.1 parts per billion.