In the Arctic, planting more trees actually makes the world warmer

In many parts of the world, planting more trees means more carbon is stored and global warming is reduced. This is the idea behind recent proposals to plant more trees in Alaska, Greenland and Iceland.

However, we recently published a paper in the journal Nature Geoscience arguing that tree planting is not a climate solution in high northern latitudes. In fact, it does more harm than good.

If we want to combat climate change, it is of course essential to reduce the concentration of greenhouse gases in the atmosphere. But other components of the Earth system also play an important role in determining whether any intervention causes more or less global warming.

One such component is known as “albedo.” This refers to the amount of solar radiation reflected back into space by the Earth’s surface. In the high latitudes of the north, snow covers the ground for many months each year. Because snow is white, it reflects about three-quarters of the sun’s energy as it covers the tundra. Therefore, snow has a high albedo.

Trees and tall plants protrude through the snow cover, darkening the ground and reducing the snow-covered albedo to less than 50% of its average value, causing additional snow to melt. In the far north, the warming effect of trees’ low albedo exceeds the cooling effect of carbon taken from the atmosphere by converting it into biomass. So, considering both the albedo and the carbon that trees can ultimately extract and store from the atmosphere, planting trees in the far north could actually warm the climate.

soil carbon released into the atmosphere

But that’s not all. Most of the carbon in the Arctic is found in soil. Arctic soil contains more carbon than all the trees on Earth combined, and this includes all the tropical rainforests. When trees grow in the Arctic, some of the carbon can be released.

That’s because even in the unlikely best-case scenario, where plantations try to minimize soil disturbance, growing trees excrete sugars through their roots. This provides nearby microbes with the tools and energy they need to break down some of the soil carbon that has accumulated over thousands of years. This process, in which the addition of new carbon from roots induces the metabolism of old soil carbon, is called the priming effect.

The inevitable consequence of reforestation projects in the Arctic is that large amounts of soil carbon will be released into the atmosphere over many decades. This is an unacceptable contribution to atmospheric greenhouse gases at a time when we most need reductions.

Forests in the far north also tend to be disturbed by other factors. For example, wildfires almost completely burn through large portions of the boreal forest every few decades or centuries. And when not burning, pests and extreme weather tend to regularly remove standing plants. All of these risks increase as the Arctic warms.

Centralized management of forests may reduce risks to some extent, but it is not possible to manage them on a large scale in remote areas. A further possibility is that people create large plantations of trees of the same age and species. This means that people reach their most vulnerable ages at the same time. Therefore, not only will standing trees in the far north contribute to further warming, but the carbon they store will also become more vulnerable.

Last, but by no means least, beyond its climate impacts, afforestation in high latitudes negatively impacts Arctic biodiversity and challenges traditional livelihoods such as reindeer herding and caribou hunting. Possibly.

We can fool ourselves, but we can’t fool the earth

So why do people plant trees in the North Pole? Local people may want to secure their supply of timber and lumber, for example, or reduce their dependence on imports. Ultimately, it’s up to them to decide whether or not to do so.

But these efforts should not be sold as climate solutions. This is not the first time we have seen carbon credits being traded without due care, contributing little to climate change mitigation yet enabling efforts to succeed. We are not fooling the Earth system, only ourselves, so it is urgent that we better account for the overall climate impact of our interventions and move away from so-called “carbon tunnel vision”. is required. A point that is equally relevant far beyond the North Pole.

But there are viable nature-based climate solutions for the Arctic and surrounding regions. For example, sustainable populations of large herbivores such as caribou and musk oxen can actually contribute to climate cooling.

This can occur directly through herbivores keeping the tundra landscape open, or indirectly through the influence of herbivores foraging in the snow. This reduces the snow’s insulating ability and helps lower soil temperatures. Large herbivores also reduce climate-induced biodiversity loss in Arctic ecosystems and remain a fundamental food resource for local communities.

Although we still don’t understand everything about how these large animals impact ecosystems, the evidence supporting their effectiveness is greater than that of many well-funded climate change mitigation efforts. is also powerful. But nature-based solutions must ultimately be led by far northern communities living on the front lines of climate change.

This article is republished from The Conversation under a Creative Commons license. Read the original article.