Why won’t reforestation have as large an impact as other sustainable alternatives?

Question

This topic really surged after the #TeamTrees movement, but has fallen off pretty significantly. I’ve heard a lot about how reforestation just doesn’t have the carbon capture capability required for it to be sustainable in the long run, but I would think that enough trees would offset at least SOME greenhouse emissions.

In: Planetary Science

Answer 1

Trees are really a drop in the bucket. They absorb carbon relatively slowly and over a long period of time, and the total absorbed per tree is quite small. I don’t remember the exact figures, but IIRC global yearly carbon emissions are somewhere on the order of several *trillion* mature trees worth. We basically don’t even have the arable land to plant that many trees, much less the money and political will.

You also have a bigger problem with this strategy, which is that its benefits are very temporary. Trees, as with all life, effectively withdraw carbon from the atmosphere and soil to grow and return it back to the atmosphere and soil when they die through decomposition. This forms a closed loop, where the amount of CO2 in the atmosphere doesn’t change very much over time, even as trees grow, die, decompose, burn, etc. Humans are artificially destabilizing this by *adding* carbon to the atmosphere which was previously sequestered underground. That additional carbon isn’t something that you can remove from the cycle easily unless you do something odd like grow trees, then cut them down once mature, encase them in something impermeable so they don’t decompose (oh look, a legitimately eco-friendly use for plastic!), bury them deep underground, and plant new trees.

No one is seriously suggesting the burying thing (which amounts to effectively making new oil to replace the stuff we’ve burned), and so the whole “plant trees” thing really isn’t a serious suggestion. I mean, trees and great and we should certainly plant lots of them, but let’s do that *in addition* to decarbonizing our civilization, because green things make us happy not because they magically geo engineer our mistakes away.