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
The oceans have been steadily rising in temperatures and they have the most impact on carbon emissions absorption. So not only are the oceans slowly becoming less effective at absorbing it, they also can release carbon emmions themselves.
Underwater heatwaves
In 2010–2011, an underwater heatwave killed large amounts of seagrass off the coast of northwestern Australia, triggering a significant release of CO2.
Trees are great, and they do indeed capture carbon, but they can only capture a little carbon dioxide per unit of land and per unit of time, and frankly we pollute WAY too fast for it to be viable. When trees die, they also rot, which re-releases some of that captured carbon; it’s only when trees are dead and buried that the carbon is gone for good.
Most of Earth’s carbon capture actually happens with ocean algae and phytoplankton. Like trees, they capture carbon dioxide through photosynthesis, but when they die they sink WAY down to the ocean floor, trapping the carbon far more efficiently than on land. Combined with the sheer surface area of the ocean, and it amounts to way more than the trees could ever deal with.
But that’s not to say we shouldn’t replant trees. Trees have other benefits beyond carbon capture, such as providing habitat for wildlife, controlling erosion, and providing shade. You can use trees in urban environments to help keep buildings and streets cooler, which also helps reduce the air conditioning use of nearby buildings, which saves power.
We are also working on algae-growing solutions for carbon capture. There’s even one company that can turn algae into cheap plastic, meaning we can potentially farm plastic products and take CO2 out of the air while doing it.
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.
Far far from an expert but here are some concerns. It will no doubt help but there are some considerations.
1) But the returns on investment are not high. It takes a lot of land, careful management and resources. There are successes and failures (monoculture, susceptibility to diseases). Overall, though, this is not as cheap or sure way to sequester CO2 as the media and certain groups portray it to be.
2) Takes a long time. Obviously trees take a long time to grow sometimes half century to a century to mature. Many feel that any efforts taken today are many decades to late to address the acute problem in the next quarter century.
3) Subject to a bit too much hype. There are multi-goal projects that make sense – say reforesting not only for carbon capture but to slow or reverse desertification. But the concern is that it can be seen as a silver bullet when it can really only be a small part of a sustainability solution.
Controversially, reforestation is used as a means of obtaining carbon credits. This has been called into question for the reasons above. Companies that take money to plant trees that do a poor job nonetheless get to sell these carbon credits to CO2 emitters.
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Where I live the forests started to die 30 years ago. They are burning every summer now too.
As you grow a forest you capture carbon. Once it’s grown the capture stops and you have to leave that land forested to keep the carbon captured. If the forest is cut down or burnt or dies then the captured carbon is released. So forests only permanently capture a fixed amount of carbon in return for permanently using a fixed amount of land.
Grown forests will have large trees dying which then rot, releasing their carbon, and new trees grow to maintain a steady state. Logging for building and paper helps a little, but almost all that timber has a very short lifespan as wood or paper products.
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