The World Meteorological Organization has confirmed a unprecedented leap in the concentration of carbon dioxide by 2024. Global measurements place the annual average at 423,9 ppm, a level unmatched in modern records and requiring a look back thousands of years to find anything comparable.
The year-on-year increase was 3,5 ppm, the highest since direct measurements began in 1957. Combining emissions from fossil fuels, an intense El Niño event, large-scale forest fires, and the reduced effectiveness of natural sinks explain much of this upswing.
Key figures of the rebound
The value of 2024 (423,9 ppm) is 52% above pre-industrial levels. Moreover, growth rates have accelerated: the annual average has increased from ~0,8 ppm in the 1960s to ~2,4 ppm between 2011 and 2020.
For context, when the WMO bulletin was first published in 2004, the annual average of CO2 was 377,1 ppmThe jump observed between 2023 and 2024 (3,5 ppm) confirms that the underlying trend is intensifying.
What's behind the jump?
In years with El Niño, land-based sinks lose effectiveness due to dry ecosystems and a higher incidence of fires. This context, combined with the continued use of fossil fuels, explains the record in 2024.
Carbon sinks in trouble
Approximately half of the CO2 emitted each year remains in the atmosphere, while the rest absorb it forests and oceansHowever, global warming reduces the solubility of CO2 in the sea, and recurring droughts put stress on terrestrial ecosystems.
The WMO warns that less efficient sinks mean more CO2 is retained and accelerated warming. Hence the importance of strengthening monitoring and understanding these feedbacks to fine-tune mitigation measures.
Methane and nitrous oxide also at their highest levels
In addition to CO2, in 2024 the methane (CH4) reached 1.942 ppb, about 166% above pre-industrial levels. This gas, with a half-life of about nine years, comes approximately 40% from climate-sensitive natural sources (wetlands) and 60% from human activities such as livestock farming, rice cultivation, landfills, and fossil fuels.
El Nitrous oxide (N2O) reached 338 ppb, 25% above the pre-industrial period, with contributions from natural processes and human practices such as the use of fertilizers, the burning of biomass, and certain industrial activities.
Despite these records, the priority remains CO2: it is the main driver of current warming (approximately two-thirds) and explains most of the increase in radiative forcing since 1990. Rapidly reduce fossil fuel emissions is key to stabilizing the climate.
With the data in hand, the diagnosis is clear: a historic rebound CO2 sinks under pressure, and greenhouse gases at record levels. Understanding the causes and addressing them—particularly by reducing fossil fuel use and strengthening atmospheric monitoring—will determine whether we prevent this escalation from becoming an increasingly difficult-to-stop warming cycle.
