The concentration of carbon dioxide (CO₂) in the atmosphere recorded its highest annual increase ever measured in 2024, reaching unprecedented levels and worsening long-term climate change prospects, according to a report published Wednesday by the World Meteorological Organization (WMO).
The global average concentration of CO₂ rose by 3.5 parts per million (ppm) between 2023 and 2024, marking the largest annual increase since modern measurements began in 1957, and reaching 423.9 ppm, as noted by the UN agency in its 21st Annual Bulletin on Greenhouse Gases.
This surge is attributed to ongoing human-induced emissions, an increase in emissions related to wildfires, as well as a reduction in the ability of forests and oceans—traditionally considered “carbon sinks”—to absorb CO₂.
“CO₂ trapped in the atmosphere acts as an accelerator of our climate, leading to increasingly frequent extreme weather events. Reducing emissions is essential, not only for the climate but also for economic security and the well-being of populations,” emphasized Ko Barrett, WMO Deputy Secretary-General.
The year 2024, marked by a particularly strong El Niño episode and record global temperatures, was conducive to fires and drought, particularly in the Amazon and Southern Africa, contributing to an increase in natural CO₂ emissions. At the same time, oceans are absorbing less CO₂ due to decreased solubility in warmer water, and terrestrial ecosystems, affected by prolonged droughts, are seeing their absorption role diminished.
“There is growing concern that carbon sinks—both terrestrial and marine—are becoming less effective, which would increase the proportion of CO₂ remaining in the atmosphere and accelerate warming,” warned Oksana Tarasova, the report’s scientific coordinator.
The report also noted record concentrations for methane (CH₄) and nitrous oxide (N₂O), the second and third most significant greenhouse gases linked to human activities.
In 2024, the average concentration of methane reached 1,942 parts per billion (ppb), a 166% increase compared to pre-industrial levels, while nitrous oxide reached 338.0 ppb, up by 25% over the same period.
The WMO calls for strengthening and sustaining greenhouse gas monitoring mechanisms, which are essential for informing global climate policies and assessing progress. The findings of the bulletin aim to illuminate discussions at the upcoming United Nations Climate Conference (COP30), scheduled for November in Belém, Brazil.
This report is part of the WMO’s Global Atmosphere Watch Programme, which coordinates global observations of greenhouse gases. It will be supplemented on November 4 by the release of the United Nations Environment Programme (UNEP) Emissions Gap Report, which will analyze the gap between current state commitments and the trajectories needed to meet the goals of the Paris Agreement.