Offsetting carbon emissions by tree planting has become the popular thing to do recently. For one, it definitely feels good(who doesn’t like planting trees), and yes it sounds reasonable and logical to offset our emissions by absorbing Co2 from the atmosphere and putting in tree branches and trunks. However, how much carbon can really be offset by doing this?
How much carbon can be stored by plants?
To put numbers in perspective, human activities cause 51 billion tons of greenhouse gases every year. Forests plantations over the world can store anywhere from 40-100Gt of C - however, it takes 100 years to reach that potential. Why? It takes time to grow a plant into a large tree, that embeds a lot of carbon in its trunk, and branches.
Assuming best case scenario - meaning humans solving land acquisition, water constraints, and neglecting the impact of climate change itself on the growth of trees, it comes to a best-case estimate of 1 billion tons of C per year, that can be embedded in trees. This is an impressive 2% - yes, it is impressive because that’s the only solution we’ve today which can even scale to this number.
Seems simple, let’s just plant trees everywhere?
If only, the reality was so simple. The more I read on ecology and ecosystems, the more I confirm the notion that - natural ecosystems are much more complex than we think they are. They also tend to be more interconnected with each other in ways yet to be figured out by science, even for seemingly obvious things
Case in point, consider China and its plans to increase forest cover from 23.04% in 2020 to 26% in 20351, it is on track to plant 35 million hectares of trees(the size of Germany) in its northern arid areas by 2050 to make a so-called Great Green Wall. There are even incentives from corporations like Alipay rewarding low-carbon acts such as renting a bike to “water” virtual trees and the organizers will plant a real tree in deserts in China when virtual trees grow up. It is amazing to see such climate action from so many people for climate change. Unfortunately, all of this has led to an unintended consequence - water scarcity.
Black locust trees were planted as part of this movement replacing natural grasslands. These new non-native trees have taken up 92% of the annual rainfall for its growth, leaving only 8% for the downstream river. It has impacted the wellbeing of 100+ million people living in the Yellow River Basin and 400 million people living further in the path of the Yellow River23. A similar thing also happens in Arctics where planting tall, dark-leaved trees causes more heat to be absorbed and retained than when land is covered in snow reflecting heat and sunlight back into space.
Where does this lead us?
I am of course not saying that afforestation is bad, but we need to be mindful of where we plant them. Forests provide a lot of ecosystem services and carbon offsets are one of them. Current research recommends the following:
We should first focus on conserving mature natural forests that provide significant additional benefits before going on generating artificial forests. They have a lot of carbon already stored in their trunks and soil (yes, forest soil accounts for more than 70% of the carbon stored in the ecosystem). That includes preserving savannas, grasslands, and peatlands as well.
Afforestation is found to be most effective with emissions mitigations when planted in formerly forested areas, instead of trying to find new areas and covering them with forests
Given the emissions from building materials is high(embedded carbon of building materials makes up roughly 9% of total global emissions), replacing steel and concrete with wood products from the forest that have a long life would not only reduce the need of using fossil fuels to create concrete and steel but also help using carbon embedded from forests. However, like everything else managing this is also not so simple. Whether transferring carbon from the forest to the built environment will reduce atmospheric greenhouse gas concentrations depends on how the forest is managed and how long the building is in service4. Using timber from certified sustainable forests ensures that these emissions can be offset. The problem is on paper, yes these certification companies talk a lot about standards, but then when it comes to implementing them on the ground, they don’t stand up to them. Many timber companies just use them to sell green-washed timber, marking up the prices and making consumers feel good about their choice of purchase.
What’s the solution then?
Using protected forests to offset carbon is not a very reliable method. The method used by companies selling carbon offsets, to estimate the emissions offset, is by trying to guess how much of this protected forest would have been deforested if they did not protect it in the first place. However, there are many assumptions in this approach, for example, if you’re paying for protecting a forest of 100 hectares, then it still does not prevent a timber company from cutting the forest area which is right next to the protected one. Unless there is a global standard backed by countries on what it means to offset “x” tons of Co2 through forests, any company could come up with its own method of estimation. And for the buyers of carbon offsets like airlines, it is very easy to go with the least unit valued offsets, especially when the entire market is under pressure to go with carbon offsets.
Current offset markets are driven by consumer choice. They pay assuming that their flight emissions are being offset by forests in Amazon. But, it very well might not be the case. Worst, everyone who paid for offsets, might involve in doing more of the activities with the assumption of net-zero
Ideally, there should be regulation for carbon offset markets. First, regulation on which forests can be considered for selling carbon offsets, and second on which type of industries can buy them. They should only be able to be bought by industries for which there does not exist an alternate solution that can work at scale - like the airline industry, or manufacturing industry. In that way, people don’t use forests for offsetting carbon emissions for things like bitcoin mining.
Paying for carbon offsets is still good because it does ensure some of the good forest management practices are being followed in the protected areas. However, it should just stop there, we should not be using this to account for carbon offsets and forget our transition to sustainable alternatives.