Planting trees at high latitudes in the Arctic could accelerate rather than decelerate global warming, argue scientists

Tree planting has been widely touted as a cost-effective way of reducing global warming, due to trees' ability to store large quantities of carbon from the atmosphere. But, writing in the journal Nature Geoscience, an international ...

As the climate continues to warm, trees can be planted further and further north, and large-scale tree-planting projects in the Arctic have been championed by governments and corporations as a way to mitigate the worst effects of climate change. However, when trees are planted in the wrong places—such as normally treeless tundra and mires, as well as large areas of the boreal forest with relatively open tree canopies—they can make global warming worse.

According to lead author Assistant Professor Jeppe Kristensen from Aarhus University in Denmark, the unique characteristics of Arctic and sub-Arctic ecosystems make them poorly suited for tree planting for climate mitigation. "Soils in the Arctic store more carbon than all vegetation on Earth," said Kristensen. "These soils are vulnerable to disturbances, such as cultivation for forestry or agriculture, but also the penetration of tree roots. The semi-continuous daylight during the spring and early summer, when snow is still on the ground, also makes the energy balance in this region extremely sensitive to surface darkening, since green and brown trees will soak up more heat from the sun than white snow."

The direct and indirect effects of afforestation on climate forcing at high latitudes and their relative magnitudes over the lifetime of a plantation. a, Plantation establishment disrupts the previously intact soil, leading to increased decomposition of microbial carbon (1), which is exacerbated by enhanced soil insulation caused by increased snow trapping and reduced snow packing (2). Growing trees exude carbon from their roots accelerating the turnover of soil carbon by root-associated microbes (3). As the plantation matures, trees darken the surface and diminish the proportion of energy reflected to the atmosphere (4). When a plantation is disturbed, the albedo increases while carbon stored in biomass decreases (5). Credit: Laura Barbero-Palacios, Greenland Institute of Natural Resources Read more

Snow reflects the sunlight back into space without converting it into heat (the albedo effect). The trees in this plantation in South Greenland reduce the albedo effect. Credit: Mathilde le Moullec, Greenland Institute of Natural Resources Read more

The Net Climate Impact (NCI) of tree planting across the Northern circumpolar region (blue=cooling, red=warming). NCI is the carbon storage in trees minus the albedo reduction effect expressed as CO 2 equivalents (CO 2 e) per unit area. CO 2 e indicates the mass of CO 2 that would need to be emitted/extracted from to the atmosphere to force a similar warming/cooling effect. Note that significant areas of the Arctic are excluded due to lack of data. Given the general northward change from cooling to warming effects, the researchers expect these areas to show mainly warming net effects. The map is adapted from Hasler et al. 2024, Nature Communications . Credit: Jeffrey T. Kerby Read more