Since trees absorb carbon dioxide (CO₂), planting has long been considered one of the most intuitively obvious ways to combat climate change. But new research – published in the journal Nature Geoscience – suggests that arctic tree planting – or any other sort of northernmost tree planting – might actually accelerate global warming.
At latitudes high up, the peculiar conditions compromise the possibility of successful tree planting. In this region, the natural effect of snow is to reflect sunlight back into space, which is referred to as the “albedo effect,” thus keeping the Earth cool. Trees, on the other hand, absorb sunlight rather than reflecting it. With the introduction of trees in regions of snow, the albedo effect is reduced; more heat is then trapped to eventually increase temperatures.
This study, by a group of international researchers, is very keen to point out that once the tree plantations reach maturity, they tend to disrupt the soil, releasing carbon locked in it into the atmosphere. The roots of new trees release carbon to the atmosphere. This fuels the microbes’ activities, increasing the carbon turnover rate within the soil. Furthermore, tree plantations trap more snow, insulating the soil, increasing its decomposition rate in the case of microbes who do eventually allow more CO2 released into the atmosphere.
It quantified impacts from Arctic tree planting in terms of a concept called Net Climate Impact (NCI). NCI refers to the difference between carbon stored in trees and the albedo-reduction effect expressed in CO₂ equivalents. This balance was obtained, thus revealing how tree planting could cool the northern region at some places and have its warming impact in most of the Arctic.
These results run counter to the popular misconception that reforestation is a global remedy for the climate crisis. Though trees do provide beneficial opportunities for CO2 absorption over much of the world’s geography, their effect varies greatly place by place. Says these scientists, efforts at reforestation would be best targeted toward maximizing net cooling effects in some places while avoiding others where planting would be likely to add to warming.
This subtle perspective makes the idea of context-specific climate solutions important, especially in such vulnerable regions as the Arctic.