Europe’s Forest Carbon Sink Faces Growing Threat from Multiple Climate Pressures
Europe’s forests are coming under increasing pressure from a combination of climate and environmental factors, raising concerns about their ability to continue acting as one of the continent’s most important carbon sinks, according to a new international study.
Forests cover around 40% of the European Union’s land area and currently absorb approximately 280 million tonnes of carbon dioxide annually, making them a critical component of the bloc’s climate strategy. However, researchers have found that the capacity of European forests to absorb carbon is declining significantly. Between 2010 and 2020, annual carbon uptake fell by almost a third, dropping from 466 million tonnes to 295 million tonnes of CO₂ equivalent.
The study, led by Professor Mana Gharun of the Institute of Landscape Ecology at the University of Münster, examined the factors behind this decline and concluded that the interaction of multiple environmental pressures makes forest responses increasingly difficult to predict.
Researchers found that while forests often respond in relatively predictable ways to individual factors such as rising temperatures, elevated carbon dioxide levels or nitrogen deposition, real-world conditions involve several stressors occurring simultaneously. These combined pressures can strengthen, weaken or even reverse expected effects.
For example, higher temperatures can extend the growing season and increase photosynthesis, potentially boosting carbon absorption. However, when warming is accompanied by drought, trees often close the microscopic pores on their leaves through which they absorb carbon dioxide, reducing their ability to take up carbon. Likewise, the benefits of increased atmospheric CO₂ concentrations can be diminished by nutrient shortages or water stress.
The study also highlights the growing importance of extreme weather events that have received comparatively little scientific attention. These include unusually warm winters, excessive rainfall and late frosts, all of which are expected to become more common as the climate changes. Researchers noted that the exceptionally mild winter of 2020 reduced net carbon uptake across numerous European forests as higher air and soil temperatures altered ecosystem processes.
Model projections cited in the study indicate that more than one-third of Europe’s forested areas could face a heightened risk of frost damage in the future. Such events can have long-lasting consequences, with climate extremes capable of reducing carbon uptake for several growing seasons or even years after the initial event.
The researchers found that the resilience of net carbon uptake has declined across large areas of temperate Europe over the past two decades, suggesting forests are becoming increasingly vulnerable to environmental stress. According to the authors, the long-term impacts of climate extremes may prove just as damaging as the immediate effects of droughts and heatwaves.
The study was conducted as part of the European CLEANFOREST initiative, which brought together 34 researchers from 30 institutions across 17 countries. The team reviewed current scientific knowledge on the effects of elevated CO₂ concentrations, drought, heatwaves, nitrogen deposition and other extreme events on forest carbon dynamics and resilience.
The authors conclude that long-term field observations, combined with advanced data science and statistical analysis, will be essential for improving understanding of how multiple environmental pressures interact and for producing more reliable forecasts of Europe’s future forest carbon sink.
