Forests as carbon source, not carbon sink

A key component in the fight against climate change has been the idea of controlled and regulated reforestation in regions destroyed by human actions. However, a recent study suggests that forests regrowing in Europe after mass deforestation between the 18th and 19th century are actually contributing to global warming rather than helping to reverse it; despite the fact they are 10% larger than the pre-industrial revolution woodlands. This poses a real problem for those hoping to reverse the effects of climate change via reforestation, with over 85% of modern European forests regulated by human management.

Researchers from the Laboratory of Climate Science and Environment in France, recreated the last 260 years of human forest management through computer modelling; taking into account, biodiversity, harvesting methods, and background temperature fluctuations. The results suggested that in the 260 years, up to 2010, the addition of 200,000 km2 to woodland in Europe led to a temperature increase of 0.12°C. This number on its own may not seem that significant, but the researchers have said that the increase in temperature equates to about 6% of the global warming attributed to the burning of fossil fuels. According to the study’s leader Dr Kim Naudts, “Even well managed forests today store less carbon than their natural counterparts in 1750”. Hence, this study calls into question how well we understand our ability to combat climate change as a global issue.

In the 260 years up to 2010 The addition of 200,000 km2 of woodland in Europe led to a temperature increase of 0.12°C

The paper argues that the key issue with the forests under human management is the change in species composition, relative to a composition which would otherwise naturally occur. More and more forest managers have chosen to replant trees that are proven to be fast growing and highly profitable to make any projects sustainable. However, trees that fit such specific criteria, such as Pine and Spruce, absorb more heat than native and previously abundant deciduous species, such as Oak or Birch; meaning more energy is retained in our atmosphere, warming the planet. Additionally, these conifer species release less cooling water into the atmosphere, which affects both the local ecosystem and the wider region. These two factors caused a 0.08% increase in temperature, along with other contributing factors such as commercial harvesting.

The idea that reforestation and, more generally, creating mass carbon sinks is the most effective way to combat climate change has been challenged before. A 1992 study in Nature presented data showing that expanded forest regions in the upper northern hemisphere could be detrimental as those regions tended to be snow covered for large sections of the year. It was found that snow, even if present only seasonally, reflected more energy than the conifer trees could.These findings may be only strictly related to European reforestation projects, since the results are so closely linked to the history of the continent. On the other hand, this process of mass deforestation and managed replanting isn’t exclusive to these regions alone, so conservation groups worldwide will need understand this situation in order not to make the same mistakes.