Why planting trees in the Arctic could make global warming worse

By Stephen Beech

Planting millions of trees in the Arctic would make global warming worse, scientists have warned.

Tree planting at high latitudes has been widely touted as a "cost-effective" way of reducing climate change due to its ability to store large quantities of carbon from the atmosphere.

But such a project will accelerate - rather than decelerate, global warming, say an international group of researchers.

Large-scale tree-planting projects in the Arctic have been championed by governments and corporations as a way to reduce the worst effects of climate change.

But, writing in the journal Nature Geoscience, the scientists warn that when trees are planted in the wrong places - such as the normally treeless Arctic tundra - they can make global warming worse.

Lead author Assistant Professor Jeppe Kristensen says the "unique" characteristics of Arctic and sub-Arctic ecosystems make them "poorly suited" for tree planting for climate mitigation.

D.r Kristensen, of Aarhus University in Denmark, said: “Soils in the Arctic store more carbon than all vegetation on Earth.

“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.”

He says the regions surrounding the North Pole in North America, Asia and Scandinavia are also "prone" to natural disturbances - including wildfires and droughts - that kill off vegetation.

Dr. Kristensen warns that climate change makes such events both more frequent and more severe.

He said: “This is a risky place to be a tree, particularly as part of a homogeneous plantation that is more vulnerable to such disturbances.

“The carbon stored in these trees risks fuelling disturbances and getting released back to the atmosphere within a few decades.”

The researchers say that tree planting at high latitudes is a "prime example" of a climate solution with a desired effect in one context, but the opposite effect in another.

Dr. Kristensen said: “The climate debate is very carbon-focused because the main way humans have modified the Earth’s climate in the last century is through emitting greenhouse gases from burning fossil fuels.

“But at the core, climate change is the result of how much solar energy entering the atmosphere stays, and how much leaves again - Earth’s so-called energy balance.”

Greenhouse gases are an important determinant of how much heat can escape Earth’s atmosphere.

But the researchers say that at high latitudes, how much sunlight is reflected back into space, without being converted into heat - known as the "albedo effect" - is more important than carbon storage for the total energy balance.

They are calling for a more "holistic" view of ecosystems to identify truly meaningful nature-based solutions that don't compromise the overall goal: slowing down climate change.

Senior author Professor Marc Macias-Fauria said: “A holistic approach is not just a richer way of looking at the climate effects of nature-based solutions, but it’s imperative if we’re going to make a difference in the real world."

The scientists recognize that there can be other reasons for planting trees, such as timber self-sufficiency, but these cases do not come with bonuses for climate mitigation.

Macias-Fauria, of Cambridge University’s Scott Polar Research Institute, said: “Forestry in the far North should be viewed like any other production system and compensate for its negative impact on the climate and biodiversity.

“You can’t have your cake and eat it, and you can’t deceive the Earth.

"By selling northern afforestation as a climate solution, we’re only fooling ourselves.”

The researchers instead suggest that working with local communities to support sustainable populations of large herbivores- such as caribou - could be a "more viable" nature-based solution to climate change in Arctic and subarctic regions than planting millions of trees.

Macias-Fauria said: “There is ample evidence that large herbivores affect plant communities and snow conditions in ways that result in net cooling.

“This happens both directly, by keeping tundra landscapes open, and indirectly, through the effects of herbivore winter foraging, where they modify the snow and decrease its insulation capacity, reducing soil temperatures and permafrost thaw.”

The researchers say it’s vital to consider biodiversity and the livelihoods of local communities in the pursuit of nature-based climate solutions.

Macias-Fauria said: “Large herbivores can reduce climate-driven biodiversity loss in Arctic ecosystems and remain a fundamental food resource for local communities.”

He added: “Biodiversity and local communities are not an added benefit to nature-based solutions: they are fundamental.

"Any nature-based solutions must be led by the communities who live at the frontline of climate change.”