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Trees capture carbon, but they don't sequester it. You need additional steps to prevent the biomass from decomposing. This isn't too hard, generally just buryin
by jjk166 4y ago
Trees capture carbon, but they don't sequester it. You need additional steps to prevent the biomass from decomposing. This isn't too hard, generally just burying plant material below enough earth will do the trick, but it's a substantial expense at scale.
And scale is really the issue. All the world's forests combined currently absorb about 20% of CO2 humans currently emit. To go neutral, you're looking at planting around 12 trillion trees. Worse still, about 30% of Earth's land surface area are already covered by forests, so you can't simply expand the forests to get the required carbon capture.
The only realistic way to achieve 100% carbon capture by biological means would be to seed algae blooms in the ocean, which for short term carbon uptake would work pretty well, but when that algae dies it is way harder to prevent it from decomposing, meaning you don't get long term sequestration. Further, you are talking about terraforming-level changes to marine environments all over the world. Beyond the catastrophic effects that can have on other species, the full effects of what that might do to us are impossible to fully predict.
Artificial carbon capture might have higher capital costs since the equipment is not self replicating, but it can be orders of magnitude more efficient in terms of energy, CO2 capture rate, and land use requirement.
- runarberg 4y agoCan’t you just use the wood for something instead? I’ve seen a lot of innovative use for wood in large construction projects. For example, there was a recent proposal to replace the West Seattle bridge with a timber through arch bridge, and timber skyscrapers are apparently now a thing. This is especially true since concrete is a really polluting industry, and finding ways to use less cement is a pretty solid climate action.
- krallja 4y agoThere isn’t enough wood used, by several orders of magnitude.
- jjk166 4y agoThere simply isn't that much demand for wood. It is already used extensively as a building material, but only a tiny fraction of the world's forests are used for lumber production. Indeed lumber production doesn't even make up a large portion of trees that humans clear. For context 12 trillion trees of lumber would be enough to build 100 to 500 two story residential homes per human being on earth. Again, this doesn't really matter since this wouldn't physically fit on the planet.
- brnt 4y agoSome say concrete should be replaced wholesale with wood (CLT). I imagine that would make a dent?
- jjk166 4y agoEvery year humans use approximately 9 Billion tons of concrete. The mass of 12 Trillion trees is approximately 1100 years worth of concrete. This much lumber would need to be used every 200 years or so.
- runarberg 4y agoI see, so we are never going to be able to use trees to capture our current current CO2 emissions. However would it be possible to use trees (and other photosynthetic organisms) to capture our historic emissions in a mass global atmospheric cleanup efforts, after we’ve mostly gone carbon neutral? Or is that also like a 1000 year effort even if we became carbon neutral tomorrow?
- jjk166 4y agoIf we stopped emmitting CO2 tomorrow, a realistic increase in number of trees (~1 trillion trees) would take about 900 years to return to pre-industrial co2 levels. The more trees you plant, the faster it goes, but even if you cover the entire planet in forest (including places like Antarctica and the Sahara), you're still looking at centuries. Other organisms can be used as well, but again you need to sequester the carbon.
- runarberg 4y agoThanks. I appreciate your answers here. This is why I love HN. Getting answers to questions on niche topics I don’t even know how to begin searching for.
- r_hoods_ghost 4y agoPretty much. I don't have the numbers but the phrase to always bear in mind is "fossil carbon." All that oil, gas and coal was once living bio matter (to a first approximation). Industrial civilisation has been predicated on us burning fossil carbon laid down over millions of years by earths organisms. It will take more than a few decades to remove the excess that we have pumped in, even if we reforest the earth, reduce the population and all become ascetics.
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- njarboe 4y agoMany trees live for over 500 years (Redwoods, Cedars, Douglar Fir, Oaks, etc.). They can be part of the solution of keeping CO2 levels down while our energy system is de-carbonized. Go ahead and plant trees. They are great in many other ways also.
- jjk166 4y agoAgain, the real deal breaker is needing 1.6 earths worth of land. No one is saying planting trees is a bad thing, but there is no escaping the need for other methods of carbon capture. Trees tend to stop growing after about 150 years, so trees left standing longer than that will delay releasing the CO2 they've already captured, but will not continue to capture carbon. Indeed you probably want to cull trees before their growth rates start to decline around the 100 year mark to maximize your carbon capture rate.
- kiliantics 4y agoHow are you arriving at the 12 trillion trees number? I think there are some less obvious ways that trees can capture more carbon. For instance, trees build soil over time. Much of the deforested land in the world has had its topsoil washed away without trees to hold it in place. That soil is also a form of captured carbon.
- stevage 4y agoSoil carbon sequestration is definitely well known. Eg https://carbonfarmersofaustralia.com.au/carbon-farming/soil-carbon-method/ https://carbonfarmersofaustralia.com.au/carbon-farming/soil-...
- jjk166 4y agoEarth currently has about 3 trillion trees, this population captures about 20% of current human co2 emissions (which includes soil creation). To get to 100%, you need 5 times as many trees, which means increasing the current population by 12 trillion. Of course this is a crude estimate, not all trees are equal and planting trees in such large numbers would undoubtedly have other effects, but no matter what you are talking about an absurdly large number.