Since 2005, the amount of atmospheric CO2 absorbed by the continent's trees has been slowing, researchers reported. Writing in Nature Climate Change, they said this was a result of a declining volume of trees, deforestation and the impact of natural disturbances.
Carbon sinks play a key role in the global carbon cycle and are promoted as a way to offset rising emissions. Writing in their paper, the scientists said the continent's forests had been recovering in recent times after centuries of stock decline and deforestation.
The growth had also provided a "persistent carbon sink", which was projected to continue for decades. However, the team's study observed three warnings that the carbon sink provided by Europe's tree stands was nearing a saturation point.
"First, the stem volume increment rate (of individual trees) is decreasing and thus the sink is curbing after decades of increase," they wrote.
"Second, land use is intensifying, thereby leading to deforestation and associated carbon losses.
"Third, natural disturbances (eg wildfires) are increasing and, as a consequence, so are the emissions of CO2."
Co-author Gert-Jan Nabuurs from Wageningen University and Research Centre, Netherlands, said: "All of this together means that the increase in the size of the sink is stopping; it is even declining a little.
"We see this as the first signs of a saturating sink," he told BBC News.