Arctic tree planting is not a climate solution Published 07.11.2024

Trees contain large quantities of carbon that they have sucked out of the atmosphere without us really doing anything. Therefore, tree-planting is a cost-effective way of reducing global warming by locking up atmospheric CO2 – a greenhouse gas – in solid biomass. It’s that simple, right?

Not everywhere. A new study entitled ‘Tree planting is not a climate solution at northern high latitudes’ published in Nature Geoscience outlines why tree-planting in the Arctic will accelerate rather than decelerate climate warming. This is actually no surprise, as the science has been clear about this, for at least two decades. Still, the surge of tree-planting projects for climate mitigation that has spread across the world over the last decade has now also entered the high latitudes, including Greenland.

The problem is that tree-planting will warm rather than cool our planet, when done in the wrong places. Naturally treeless landscapes, such as on the tundra, are such places. Researchers from the Greenland Institute of Natural Resources joint with colleagues from international institutions, including Aarhus University and Cambridge University, explain why Greenland and other northern regions are poorly suited for tree planting for climate change mitigation (Figure 1). First, soils in these regions of the world store more carbon than all vegetation on Earth. This is vulnerable to disturbances, such as cultivation by planting trees and the subsequent penetration of tree-roots. Secondly, the semi-continuous daylight during the spring and early summer, when snow is still on the ground, makes the energy-balance in this region extremely sensitive to surface darkening. A needleleaf forest reflects 3-4 times less incoming solar radiation compared with a snow-covered open tundra (i.e., forests reduce the albedo). Finally, the Boreal and Arctic regions are prone to natural disturbances that kill off vegetation frequently, such as wildfires, insect outbreaks and droughts boosted by climate change. Even if a plantation makes it to maturity, this region of the world is a risky place to be a tree, and the carbon temporarily stored in its biomass will likely be prematurely released back to the atmosphere.

The Authors state that tree-planting in the Arctic is a good example of how a solution that has a desirable effect on climate in one context can have the opposite effect in a different context. While carbon storage is a way of reducing the atmospheric content of greenhouse gases regulating how much heat from the sun escapes back to space, albedo is a crucial determinant of how much sunlight is converted to heat in the first place. In certain contexts, such as in snow-covered systems, it is more important than carbon fluxes for the total energy balance. In Greenland specifically, authors specify that juniper is the only native coniferous ‘tree’. However, they do recognise that there can be other reasons for planting trees, such as for timber self-sufficiency. They warn that by selling northern afforestation as a climate solution, we are going ‘the wrong way’.

But is there nothing that can be done at high latitudes to moderate global warming then? Yes, there are alternatives more aligned with other aspects of nature-based solutions, namely biodiversity and thriving local communities. The paper proposes that ensuring sustainable populations of large herbivores may actually be a more viable nature-based solution to climate change in high-latitude systems. This happens both directly, by increasing the albedo in keeping the tundra landscapes open, and indirectly, as winter foraging modifies the snow conditions decreasing its insulation capacity, and therefore reducing soil temperatures and hence permafrost thaw. Last, but not least, large herbivores have a demonstrated capacity to reduce climate-driven biodiversity loss in Arctic ecosystems and remain a fundamental food resource for local livelihoods. Biodiversity cannot end up further damaged because of our interventions in landscapes, and these actions, should stem from and be led by the northern latitudes’ communities, which are at the frontline of the impact of climate change.

Figure 1. How planting trees in high-latitude areas impacts climate, both directly and indirectly. On the tundra, most carbon is stored in the soil, with a smaller portion stored in aboveground vegetation. The landscape is covered of snow that reflects a large amount of sunlight back into the atmosphere due to its high albedo. When trees are planted, the soil is disturbed and release carbon from the ground, increasing CO2 release to the atmosphere. Additionally, the darker surface created by the trees reduces solar reflection, absorbs heat and warms up the soil. The shift from mostly underground carbon storage to aboveground storage in trees is more vulnerable to disturbances over time, for instance to wildfires. Designed by Laura Barbero-Palacios.

For further information, contact:

Mathilde Le Moullec malm@natur.gl

Laura Barbero-Palacios labp@natur.gl

Katrine Raundrup kara@natur.gl

Ida Bomholt Dyrholm Jacobsen idja@natur.gl