Afforestation in the Arctic only a sham solution to global warming
In Arctic regions, afforestation can accelerate warming rather than slow it down, warns a new study. Instead of planting trees, researchers recommend preserving open tundra and large herbivores.
Trees are generally regarded as helpers in the fight against climate change. Their ability to absorb and store carbon dioxide from the atmosphere makes reforestation or afforestation a popular natural and cost-effective climate protection measure that is often used to offset emissions. But how effective is this method at slowing down global warming?
A new study published in Nature Geoscience in November 2024 shows that In high northern latitudes, this measure can have a counterproductive effect – and even accelerate warming.
An international research team led by the Universities of Cambridge and Aarhus and involving the Greenland Institute of Natural Resources has investigated the climatic consequences of afforestation in Arctic and sub-Arctic regions. The conclusion is clear: the special ecological characteristics of these landscapes – characterized by tundra, peatland and boreal forests – make them unsuitable for large-scale tree plantations in the interests of climate protection.
“Soils in the Arctic store more carbon than all vegetation on Earth,” explains Jeppe Kristensen, assistant professor at Aarhus University and lead author of the study, in a university press release. “These soils are vulnerable to disturbances, such as cultivation for forestry or agriculture, but also the penetration of tree roots.”
If the top layer of soil is broken up, for example by planting trees, stored carbon can escape into the atmosphere in the form of CO2 and thus increase global warming.
Trees absorb heat
Trees also change the radiation balance of Arctic ecosystems – an effect that has often been underestimated in climate protection debates. Snow-covered open tundra areas reflect a large proportion of solar radiation back into space (albedo effect), while a coniferous forest reflects three to four times less solar radiation and absorbs significantly more heat.
If these areas are replaced by dark vegetation, they absorb significantly more heat.
“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, […]”, says Kristensen. During this phase, a darker land surface can significantly shift the temperature balance.
In addition, the Arctic regions in North America, Scandinavia and Russia are increasingly affected by natural disturbances such as forest fires and droughts. As climate change progresses, such events are increasing in intensity and frequency.
“This is a risky place to be a tree, particularly as part of a homogeneous plantation that is more vulnerable to such disturbances,” says Kristensen. “The carbon stored in these trees risks fuelling disturbances and getting released back to the atmosphere within a few decades.”
Energy balance just as important as greenhouse gas emissions
In their study, the researchers criticize the fact that the climate debate often focuses exclusively on carbon emissions, while other factors are ignored.
“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,” explains Kristensen. While carbon sequestration by trees is a significant climate factor in temperate latitudes, the albedo effect plays at least as important a role in the overall energy balance in polar regions.
More large herbivores instead of reforestation
Instead of reforestation, the researchers are proposing alternative, ecologically adapted solutions. These include the targeted promotion of large herbivores such as caribou.
“There is ample evidence that large herbivores affect plant communities and snow conditions in ways that result in net cooling,” says Professor Marc Macias-Fauria of the Scott Polar Research Institute at the University of Cambridge and senior author of the study in the same press release.
The animals prevent the spread of woody plants and reduce the insulating effect of the snow cover through their activity in winter – with positive effects on soil temperature and permafrost.
The authors emphasize that nature-based solutions must also take local social and ecological realities into account.
“Large herbivores can reduce climate-driven biodiversity loss in Arctic ecosystems and remain a fundamental food resource for local communities,” says Macias-Fauria. “Biodiversity and local communities are not an added benefit to nature-based solutions: they are fundamental.”
The researchers therefore call for a differentiated view of nature-based solutions: What seems useful in one ecological context can lead to undesirable side effects in another.
“Forestry in the far North should be viewed like any other production system and compensate for its negative impact on the climate and biodiversity,” says Macias-Fauria. “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.”
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