Planting trees is perhaps the best and most widely-known mitigative measure when it comes to climate change. However, a new study published Friday in the journal Science posits that planting the wrong kind of trees may, in practice, stoke global warming.
Researchers found that even though Europe’s green canopy has increased drastically over the past 250 years, a shift from lighter-colored broadleaved species, such as oak and birch, to darker-colored conifers actually had a negative climate impact. According to the study, this “species conversion” not only failed to cool the climate, it raised surface temperatures by 0.12 degrees Celsius (0.2 degrees Fahrenheit) by increasing the absorption and retention of heat.
“Afforestation and forest management are recognized as key strategies for climate change mitigation in the Paris agreement within the United Nations Framework Convention on Climate Change,” the Max Planck Institute for Meteorology in Hamburg, Germany, said in a statement. “Afforestation and forest management are generally expected to have the potential to slow global warming by removing carbon dioxide from the atmosphere. However, the new study shows that, despite a considerable increase in forest area and the onset of widespread production-oriented management since 1750, European forests failed to realize a net carbon dioxide removal from the atmosphere.”
For the purpose of the study, the researchers reconstructed and analyzed 250 years of forest management history in Europe, and found that currently, nearly 85 percent of the continent’s trees were managed by humans — as opposed to the pre-industrial era, when these forests ran wild. Between 1850 and the present day, foresters have been planting faster growing, more commercially valuable trees such as a Scots pine and Norway spruce, whose darker leaves absorb more solar radiation that their deciduous counterparts.
Moreover, as a result of the shift in composition of the forests and an increase in harvesting of wood, these trees now hold 3.1 billion tons less carbon than they did in 1750.
“The current assumption is that all forest management and all forests contribute to climate mitigation,” lead author Kim Naudts from the Max Planck Institute told Scientific American. “We cannot say that is true, at least for Europe.”