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Comment by rgossiaux | Hacker News Reader

>So we will probably need to recapture CO2 as well – or rather we will need to develop the necessary tech first.

Maybe this is a stupid question, but isn't the necessary tech "planting trees"?

The main problem with trees is they’re very slow. It would take decades after we started planting billions of trees a year before they’d have grown to the extend where they’d have captured reasonable amounts of carbon.

So, yes, it’s an option. But it’s a slow option we’d need to start implementing immediately if we wanted it bear fruit.

(We produce enough CO2 that it takes 40 billion hardwood trees growing for 40 years to sequester as much CO2 as we make in a year. We’d have to plant a lot of trees, and then not touch them for years, to affect the course of things)

If you pants trees om every bit of avaliable land, that stilll would not be enough to compensate for the emissions - we use a lot of land for farming, and are emittinghundreds of years wortg of tree-catrure per decade.

A tree captures CO2 temporarily. We would have to bury the wood to actually remove it from the atmosphere.

You are aware that "temporarily" in this context is the lifespan of a tree, right? Trees live anywhere from several decades to 20+ centuries, and their remains, once broken down, provide nutrients to the soil so more trees can grow.

Also the tree is not capturing carbon, instead emitting, half of the year if not planted in the optimal places near the equator. And it's carbon neural or negative once almost fully grown.

Hence why you need to cut them down and bury.

That's not true. Trees metabolize year round, and they literally breathe CO2.

Once a tree is fully grown it essentially stops capturing CO2.

Again, that is not true. Trees need CO2 for respiration. Basic biology, folks.

Basic biology should tell you that the only thing that counts for carbon capture is biomass added. Anything that the tree does that doesn't permanently add to its mass can't capture carbon permanently. Hence, once a tree stops growing, it stops capturing carbon. It still respirates because it does things that require energy, but any carbon it captures doing so is released fairly quickly again, e.g. when the leaves it produced in spring fall off and rot. Of course many trees keep growing a little even after they reach maturity, but the rate of growth is minuscule. A mature stable forest stores a large amount of carbon, but it hardly captures any more.

Well, you know what? Plants reproduce, too.

And, BTW, trees don't stop growing. They keep adding mass in their trunks. Literally the first google hit for "do trees stop growing": https://earthsky.org/earth/what-makes-a-tree-stop-growing

Edit: guess what? They even grow faster as they get older! https://www.npr.org/2014/01/16/262479807/old-trees-grow-fast...

That is a different point.

Anyway, the land we have is limited. You literally can't cover the planet in one big forest to capture the gigatons of carbon we have released. You have to do active forest management and store the carbon somewhere stable, for example as biochar.

Reducing the numbers of those pesky humans would help.

You can't reduce the number of humans quickly enough without a genocide.

Doesn't mean we still don't need to reduce numbers for long term sustainability.

That's the one thing climate change is good at once it gets bad. I thought we wanted to avoid this?

No. The one thing we want to avoid is making the Earth into an unlivable hellscape for those who remain alive.

They breath oxygen, they "feed" on CO2, once fully grown they need less food and that changes the balance

No, that is wrong. Plants emit O2, and consume CO2. This is called respiration.

You are mostly right, but some of that carbon does sink into the soil and get captured for much longer periods, and some of that will will sink further and likely never see the surface of the earth again unless someone digs it up.

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