The Earth's atmosphere is now registering the highest levels of carbon dioxide since modern measurements began: the average has reached 423,9 ppm , according to the latest bulletin from the World Meteorological Organization (WMO). This milestone is accompanied by the largest year-on-year increase observed since 1957, a rise of 3,5 ppm between 2023 and 2024.
Far from being an isolated finding, WMO experts warn of a vicious climate cycle : we continue to emit CO2, natural sinks absorb less, and warming intensifies. The report is being released just weeks before COP30 in Belém, Brazil, a meeting where governments are expected to take more ambitious measures.
An unprecedented leap in measurements
The bulletin data shows that the rate of increase in CO2 has tripled since the 1960s : from 0,8 ppm per year then to an average of 2,4 ppm between 2011 and 2020. From 2023 to 2024, the jump was even greater, at 3,5 ppm, the highest since continuous measurements began in 1957. To put this into context, when the WMO published its first bulletin in 2004, the annual average was 377,1 ppm; today it is approaching 424 ppm and is well above the reference threshold of 350 ppm.
It's important to distinguish between concepts: emissions are the gases released by our activities, while concentration is what remains in the atmosphere after absorption by oceans and terrestrial ecosystems. Approximately half of the CO2 emitted each year remains in the air, and the rest is captured by these sinks—a storage system that is not permanent and whose effectiveness is under pressure.
“The heat trapped by greenhouse gases intensifies extreme weather events,” the WMO summarizes in its bulletin. In the words of its Deputy Secretary-General, Ko Barrett , reducing emissions is not just a climate issue: it is key to economic security and the well-being of communities.
The magnitude of the current level is unprecedented in our recent history. Paleoclimatic estimates indicate that similar amounts of CO2 have not been seen for about three million years , when the planet was considerably warmer and sea levels were several meters higher than they are today.
Weakened carbon sinks and the El Niño factor
The oceans absorb less CO2 as the water warms because the gas's solubility decreases . On land, drought and heat stress reduce the capacity of forests and soils to sequester carbon. In 2024, a strong El Niño event dried out vegetation and fueled large fires in regions such as the Amazon and southern Africa, factors that amplified the increase in CO2 concentrations.
The result is a feedback loop: more heat means less natural absorption and, therefore, more CO2 accumulating in the atmosphere. The WMO attributes the record spike in 2024 to a combination of continued emissions, wildfires, and the decline in the capacity of ocean and land-based carbon sinks in what was also the warmest year on record.
Oksana Tarasova , the scientist in charge of the bulletin, warns that the loss of efficiency of carbon sinks could leave an even greater fraction of CO2 in the air and accelerate warming. Hence the importance of sustained and strengthened monitoring of these gases, a task in which the WMO's Global Atmosphere Watch network plays a central role.
This context explains why, even if emissions were drastically reduced tomorrow, some of the warming would continue to manifest itself for centuries: CO2 remains in the atmosphere for a long time and its climatic “tail” is long.
Methane and nitrous oxide: the rest of the cocktail
CO2 shares the spotlight with other long-lived greenhouse gases. Methane (CH4) reached an average of 1.942 ppb in 2024, around 166% above pre-industrial levels. Approximately 40% comes from natural sources (wetlands) and 60% from human activities such as livestock farming , rice cultivation, fossil fuel extraction, landfills, and biomass burning.
Nitrous oxide (N2O) reached 338,0 ppb, nearly 25% above pre-industrial levels. This gas originates from both natural processes and the use of fertilizers, biomass burning, and various industrial activities. Although present in smaller quantities than CO2, its warming potential and upward trends reinforce the outlook for prolonged global warming.
Bulletin highlights : 423,9 ppm of CO2 in 2024; annual jump of 3,5 ppm; CO2 growth rates tripled since the 1960s; methane at 1.942 ppb and N2O at 338,0 ppb; and reduced sink efficiency exacerbated by extreme conditions and El Niño.
Everything suggests that the margin for maneuver is narrowing, but it's not closed: accelerating emissions reductions, strengthening the protection of carbon sinks , and maintaining robust atmospheric monitoring are essential steps. With COP30 just around the corner, the data leaves little room for doubt and plenty of room for coordinated action.
