Abstract

Afforestation and forest management are considered to be key instruments in mitigating climate change. Here we show that since 1750, in spite of considerable afforestation, wood extraction has led to Europe’s forests accumulating a carbon debt of 3.1 petagrams of carbon. We found that afforestation is responsible for an increase of 0.12 watts per square meter in the radiative imbalance at the top of the atmosphere, whereas an increase of 0.12 kelvin in summertime atmospheric boundary layer temperature was mainly caused by species conversion. Thus, two and a half centuries of forest management in Europe have not cooled the climate. The political imperative to mitigate climate change through afforestation and forest management therefore risks failure, unless it is recognized that not all forestry contributes to climate change mitigation.

Removing trees in an organised fashion tends to release carbon that would otherwise remain stored in forest litter, dead wood and soil.

Choosing conifers over broadleaved varieties also had significant impacts on the albedo – the amount of solar radiation reflected back into space.

“Even well managed forests today store less carbon than their natural counterparts in 1750,” said Dr Kim Naudts who carried out the study while at the Laboratory of Climate Science and Environment in Gif-sur-Yvette, France.

Speaking to Science in Action on the BBC World Service, she said: “Due to the shift to conifer species, there was a warming over Europe of almost 0.12 degrees and that is caused because the conifers are darker and absorb more solar radiation.”