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Comment by jimworm | Hacker News Reader

For all the carbon capture that the Devonian/Carboniferous period did over 100 million years, humanity undid a large part of it in 150 or so years. And now to preserve human civilisation in some form, the most direct way is probably to rebuild that carbon sink within a much shorter time. Much shorter than 150 years, not 100 million.

Current carbon emissions are over 10 billion tonnes per year, so the capture speed will have to exceed that by however much required, probably something like 10x as much. If a process could be scaled to capture 100 billions tonnes of carbon per year, it could be a viable way out of the mess.

Is it even possible with current technology given unlimited funding and political will? For example, if insoluble carbonates could be synthesised from atmospheric carbon dioxide, that could be a form of long-term carbon storage.

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In theory, a sink large enough to bring the Earth back to carbon neutral would be possible if the Sahara were reforested[0]:

> The team's calculations suggest the forested deserts could draw down around 8bn tonnes of carbon a year, about the same as emitted from fossil fuels and deforestation today.

https://www.theguardian.com/technology/2009/nov/04/forests-d...

Edit:

> if insoluble carbonates could be synthesised from atmospheric carbon dioxide

indeed, if only there was a highly efficient process that could convert the carbon in the atmosphere into hydrocarbons, using energy purely from the sun...

Trees with their own conversion capacity are indeed a good interim solution, but in the long term this form of carbon storage isn't as permanent as rocks, especially given how prone trees are to dying and decaying in the biosphere of today. The Devonian didn't have that problem. For example, parts of the Amazon have become greenhouse gas emitters even when human-caused deforestation is discounted.

There's also the very real possibility of forest fires releasing huge amounts of carbon at once. Even dead trees preserved in peat bogs could burn and release carbon in this manner.

Rocks have their own weaknesses such as ocean acidification, but relatively speaking they're much more stable.

Can't you just bury the trees?

Overall, we are actually very terrible at understanding global consequences. Earth as a dynamic system is just too big and interdependent. Yet Earth's biosphere has recovered from cataclysm after cataclysm. Usually at the expense of 90%+ extinction. A big reason the carboniferous period happened is because fungi had not yet developed the capacity to digest cellulose. We're in a different regime now, and there is no telling what will happen. But one thing I think is pretty clear: we aren't going to tech our way out of this and make up some magic carbon sink. So the Earth is probably headed for a really hot period with lots of carbon in the cycle, until it stumbles on a new way to sink it. Either that, or it will head towards a semi-permanent desert planet.

Thank you, I was just about to jump in and point out the obvious. Tech has blinded us to all solutions...except more tech.

In a sense, ecological engineering _is_ tech. But trees are the most perfect tool for the job of carbon capture. They don't even require much maintenance!

According to a video I watched, reforesting the sahara comes with its own huge problems. Dust clouds from the sahara travel the atlantic to the Amazon rain forest, where it allegedly plays an important role in sustaining the Amazon.

In short, green Sahara would turn the Amazon Rainforest in the new Sahara. And that will then have its own massive implications etc...

I've thought about it myself and the best answer that comes to mind is clear-cutting entire forests, tossing that biomass down a mineshaft, and replanting to start the process over again. All this talk of planting trees removes atmospheric carbon, but until it's out of the system entirely we're one forest fire away from wiping out decades of carbon removal.

You might be interested to learn of Climeworks if you're looking for a more reliable way to remove emissions than planting trees (which is, indeed, mostly not really working as well as too slow).

I've seen those designs but never looked too deep into them. Maybe I've seen too many of the 'collect water from thin air' devices and become cynical. If their 90% efficiency is counting manufacturing and power costs then it could be worthwhile in cities and other areas with high atmospheric carbon levels. Same problem as the trees though, if we leave them out or use them for something they'll break down and be back in the carbon cycle. However we collect the carbon we need to lock it in place.

I would guess that 90% does not include R&D and is only about the general production costs like from manufacturing and building. So with scaling up (if they don't do R&D but just add a plant) it should be 90%.

It's a good question though, perhaps worth asking them.

This looks a lot like what I was thinking of. They don't provide much information about their extracting filter, but after the CO2 is extracted it is compressed into water creating carbonic acid, then injected it into a suitable basalt formation with an impermeable cap so that carbonate salts could form[1]. They claim all the injected CO2 could become carbonates in under 10 years[2].

If this works like they say, then it's cause for hope.

[1] https://www.carbfix.com/how-it-works

[2] https://climeworks.com/co2-storage-solutions

Do not clear-cut forests. You will obliterate the biome that is the understory. It's like giving yourself a haircut and removing your scalp down to the skull.

Okay, good point. Maybe turning the entire Amazon into a reverse coal mine would do more harm than good. I still think we need long-term carbon storage and using pre-existing timber seems like a good first step. If there's a better capture solution in terms of tonnes/KWH/year go with that, but tossing trees down a hole is a good example.

Yep, my favorite currently as well: https://cbmjournal.biomedcentral.com/articles/10.1186/1750-0...

10 Gigatonnes a year at a stable rate with an initial large bonus amount for the first decade or so. More if you bury more than the core logs. Burial isn't as bad as needing old mineshafts either, a small, deep pit something like 25m square is enough to bury 1km square of logged materials.

There are still issues with this proposal such as the potential for land degradation and biodiversity loss but good potential for mitigating these things as well. The main sells to me are that a) all the tech to get started today exist and are widely deployed and b) it results in carbon being re-interred in a fairly direct reversal of what we've been doing to dig it out.

I’ve been doing a lot of research in the space and the most damning part of it all is that our civilization’s carbon capture capacity is not there yet. We don’t have the technology to do that — yet. That’s why one of the most impactful things we can do is support the technology companies in developing this technology.

There are 7 billion people on the planet. Couldn't we just... have everyone plant a few trees? Trees weigh something like a quarter of a ton+ when fully grown, and pull directly from the atmosphere. Even if we remove the 50% of people who live in cities without yards, if every rural human planted 5 trees a year we'd end up sequestering a lot of that carbon, right? I know it's not permanent but if you just keep planting trees you can easily buy yourself 20 years with the open space we have.

Planting a tree won't do much on its own. It must survive and grow. The thing is, a lot of places where trees thrive are already covered with forest. With 7 billion people, you cannot sacrifice much of the arable land either.

Israelis have been reforesting their country for about 100 years and they have the best results on Earth (at least percentage-wise), but even they face bad odds in really dry places like the Negev desert.

https://aardvarkisrael.com/the-reforestation-of-israel/

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