Under normal conditions, terrestrial ecosystems act as "lungs" that compensate for our emissions: plants capture CO₂ through photosynthesis and store it in trunks, roots and soils. However, a new article published in the journal Nature Communications warns that this balance has been broken on a global scale. The research team has observed that, during 2024, the first year in which the global average temperature exceeded 1.55ºC compared to the pre-industrial era, extreme heat combined with high humidity drastically altered this balance. Specifically, the results indicate that 2024 recorded the highest peak of CO₂ in the atmosphere since measurements began in 1958. Most worryingly, most of this net increase was not due solely to human activity, but to the fact that ecosystems lost their ability to act as sinks. The main cause was an unprecedented increase in ecosystem respiration: the heat and humidity linked to a prolonged El Niño episode accelerated plant respiration, activated soil microorganisms and accelerated the decomposition of organic matter, massively releasing CO₂.
The study confirms that a vicious cycle can be generated: combined extreme events, such as a very rainy spring followed by an extremely hot summer, trigger the respiration of ecosystems. This releases more CO₂ into the atmosphere, which in turn further intensifies global warming.
Josep Peñuelas, CSIC researcher at CREAF and co-author of the study
To carry out the research, the team used state-of-the-art satellite data (such as the OCO-2 system) and global estimates of photosynthesis and fire emissions, comparing data from 2024 with that from 2022, a year considered a reference for "normal" climate.
Bushes and meadows, the most affected
Although the phenomenon was global, the effect was particularly intense in grasslands and scrublands, which contributed to 49% of the emissions anomaly, followed by forests (33%) and agricultural lands (18%). "In scrublands and grasslands, heat and humidity have a more direct impact on the soil and low vegetation. Thus, microorganisms are more active and plant respiration is accelerated," explains Peñuelas. The study clarifies that, although respiration was the dominant factor, large fires in regions such as Canada and Siberia, and droughts in tropical areas, also reduced the capacity of the biological CO₂ sink.
The loss of carbon absorption capacity was widespread , particularly affecting the eastern United States, Europe, western Siberia, Southeast Asia and large areas of South America and Africa. In addition, Peñuelas warns that the Mediterranean region is especially vulnerable: "Our interior forests and scrublands are at risk of turning from sinks to net emitters due to the consecutive heat waves they suffer with increasing frequency."
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Urgent management and mitigation
To reverse this trend, the authors propose urgent solutions. On the one hand, adaptive forest management with the aim of reducing the risk of large fires that release massive peaks of carbon. They also advocate regenerative agriculture , which implements practices that maintain and increase the organic matter stored in the soil. Finally, they point out that fossil fuel emissions must be drastically reduced : "If natural ecosystems are losing their capacity to absorb the CO₂ we emit, it is even more essential to reduce the emissions we generate," adds Peñuelas.
The study is part of the European project CONCERTO , which seeks to understand how climate and ecosystems interact. The results show that, to predict the future of the climate, it is no longer enough to look at chimneys and exhaust pipes; it is vital to understand how nature responds to new climate extremes to improve prediction models and mitigation strategies.
Article Reference: Dong, G., Jiang, F., Ju, W. et al. Dramatic increase in ecosystem respiration causes record-breaking atmospheric CO₂ growth rate in 2024. Nature Communications (2026). https://doi.org/10.1038/s41467-026-72189-y
