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Forests cover about 40% of the EU's land area. Between 1990 and 2022, they absorbed around 10% of the continent's man-made carbon emissions. However, the carbon dioxide absorption capacity of forests, also known as carbon sinks, is becoming increasingly weaker.

This is shown by calculations of multi-year carbon budgets by an international team of researchers in a . The continuous decline in the carbon sink of our forests jeopardizes the EU's climate targets. To halt or reverse the trend, the authors recommend practical measures in research and forest management.

Forests absorb carbon dioxide (COâ‚‚) from the atmosphere, which they use for their metabolism and convert into biomass. Healthy and growing forests therefore act as carbon sinks, storing climate-damaging COâ‚‚ from the atmosphere in the long term.

Forests are the strongest natural carbon sink on land in the EU, but this function is under threat: between 2020 and 2022, the average carbon sink decreased by around 27% compared to the average value for the years 2010 to 2014. This is according to the EU greenhouse gas inventory published by the European Environment Agency in 2024.

The new figures for 2025 paint an even bleaker picture, with an even greater decline in the sink. If the trend continues, the EU will miss its target set in Regulation 2018/841 to save an additional 42 million tons of COâ‚‚ equivalents by 2030 compared to the average for the period 2018 to 2020.

Causes of declining carbon uptake

Between 1950 and 2020, EU forests more than doubled their biomass and roughly tripled their carbon sequestration capacity. This was due, among other things, to reforestation after the war years, improved forest management, new energy sources replacing wood, and increased nitrogen inputs.

The decline in carbon uptake now being measured has several causes. Timber harvesting has increased and climate change is leading to more frequent heat waves and droughts, which are impairing plant growth. This has reduced the biomass of trees and thus their capacity to absorb carbon dioxide.

Climate change is also making sporadic threats to forests from insect infestations, storms, tree dieback, and forest fires more frequent and more severe. This is exacerbated by the fact that EU forests are not very resilient: around 30% consist of monocultures, which are more susceptible to climatic influences and pests.

These factors place a significant strain on forests in the EU and thus on their function as carbon sinks.

"Our research has been warning about these effects of climate change and climate extremes since the heat wave of 2003. Now it has been confirmed: they not only affect ecosystems in the short term, but also weaken the carbon uptake of our forests in the long term," states Prof. Markus Reichstein from the Max Planck Institute for Biogeochemistry in Jena, Germany, who was significantly involved in the study.

However, a weakening of carbon uptake is also occurring in other forests around the world, as research at the Max Planck Institute has shown for tropical forests in the Amazon.

Recommended actions

The consequences of climate change on carbon sinks require countermeasures on several levels: reducing greenhouse gas emissions, managing forests to make them more resilient to future climate conditions and extreme weather events, and adapting timber harvesting practices. In addition, we need better and more timely monitoring of all carbon stocks and of the health of our forests. These measurements should provide reliable data to develop the necessary policy and practical measures to restore forest carbon sinks and maximize their resilience.

"However, relying solely on natural carbon sinks is risky. Rather, those who reduce emissions will be rewarded many times over—with fewer climate extremes and, as a result, forests that can once again bind more carbon," concludes Reichstein.

The study outlines specific measures in the areas of forest monitoring, modeling, and forest management to prevent the decline of the forest carbon sink. Implementing these measures could advance the EU's 2024 Renaturation Act, several EU regulations, and its climate neutrality goal.

In addition to calling for integrated measures, the study presents an accompanying research roadmap as a guide for the necessary policy decisions. If timely regulations are combined with incentives for sustainable practices, the EU can still reverse the decline of its forests and maintain its expected contribution to climate neutrality by 2050.