Can't we just plant trees

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TL;DR

Hot take

Yes we need to plant trees! They absorb CO2 as they grow. But trees are not an entire solution.

The volume of excess, human contributed CO2 in the atmosphere is much bigger than trees can absorb, and trees are not permanent. Like when they burn, the CO2 goes back into the atmosphere.

Explanation

A lot of carbon offset schemes involved planting trees. The theory is regulators vouch that the trees exist and there are plans to keep the trees alive for a minimum time period like 100 years. The tree owners get a form of certificate or credit that they can sell to others. So when you’re paying to offset your flight the airline is buying one of these certificates. Yay the trees are growing so my Boeing keeps going!

The problem is a lot of times these schemes are bullshit. There can be integrity issues with the certification process, the projects themselves might not exist or not to the extent promised and more.

Just like how not all calories are equal, not all carbon offsets are equal either. The amount of carbon a tree absorbs is only estimated, not actually measured so the offset might not match what is expected.

There’s documented evidence of logging in rainforest carbon projects in places such as Papua New Guinea.

Fires

Forests also burn. The clever people behind the tree planting project thought about this and they plant more trees than expected, to over-compensate. So a little bit of burning is OK. It’s called a buffer pool. Except the buffer pool is running low already.

Monoculture

Similar problem with disease. If you’re going to plant trees to prioritise carbon removal then you’re going to focus on only a few tree species. This leads to a lack of genetic diversity. If a disease takes hold it can spread from tree to tree and take out massive swathes of the forest.

Permanence

The 100 years part is also a challenge - not only how do you ensure the continuity of the business behind the scheme but government laws and regulations need to be consistent as well. If a future government decides that the land the forest is on should be used for something better, then the trees are gone and all those offsets are mostly meaningless (depending what happens to the trees).

Where

It turns out that where on earth you plant trees can also have an impact on the albedo - or shininess of the earth. Why does that matter? It impacts the amount of sunlight reflected back to space - the less reflected, the warmer we get. So even well-intentioned, high-quality tree-planting projects could be having a smaller or larger impact than they expected. There’s some research on this here.

So?

Planting trees is awesome and we should definitely do it. We need all the things. But we shouldn’t be leaning too heavily on it as an excuse to keep releasing greenhouse gases in the atmosphere.