Yeah, I mean I think carbon capture is kinda stupid on one level. It's like an excuse for us to not change our behavior

You are right.

But it’s less certain.

There’s a decent amount of carbon emissions associated with management of land, however, and if you want the land to continue to be optimised for carbon sequestration you’ll need to manage it and, besides, in most areas you can’t just buy land, plant some trees on and leave it - it’ll need active management to stay a forest and to comply with local regulation.

But let’s say you’re doing that and planting for carbon sequestration, then you’d probably choose something like pine (fast growing, absorbs a lot of carbon, stays green through the year so tends to prevent competition on the floor). A tree that like will absorb roughly a tonne (1000-1100 kg of carbon) in its life. Then it dies and you’ll need to remove it to ensure a new tree can grow (otherwise it’ll be taken over by other species slowly).

A hectare of dense pine trees can probably hold 3000 trees (if we are being generous) so a hectare (100x100 metres of land) can hold 3000 tonnes of carbon. On average in Europe we emit about 9 tonnes of carbon per year and live for 80 years so a hectare can hold about 4 people’s worth of life time emissions.

In the U.K. you’ll end up spending about £25,000 for a hectare of woodland (give or take), but then you’ll need public liability insurance and management fees (let’s just say £20/year for for a hectare of insurance and £750/year for management of a hectare) … so let’s assume £800/year for a hectare or £200/year to manage the size of woodland required to absorb a person’s life time emissions (remember, 4 people per hectare). Now you need a trust manager who runs it, permanently forevermore, to manage it all. Let’s say £40,000/year and assume that they manage 1000 people’s life time emissions (this obviously could scale down to almost zero as the scheme grew) or £40/year per person.

But don’t forget additionally: This has to be NEW woodland, so you need to buy non-woodland and then plant the woodland. Otherwise you’re not absorbing more carbon. Typical quotes for a hectare of pine planting will be about £4000.

And this cost needs paying forevermore: £6000 to buy the space for a person’s emission £4000 to plant it £250/year to manage it (insurance, management)

To deliver £250/year you’ll need an investment of 250/0.04=£6250. Let’s just say £7000 to leave some buffer for bad years and to pay for the additional carbon that’s emitted from the management. So:

£6000 to buy the space for a person’s emissions. £4000 to plant it.
£7000 to manage it forevermore.

So all in you’ll need to spend £17000 to absorb your lifetime’s worth of emissions.

Now let’s compare that to geological sequestration. Climeworks, the only publically available scheme to suck carbon out of the air and sequester it into rock, permanently, quotes £1100/ton of carbon. So to extract the 720 tones you’ll emit in your lifetime it would be £792,000.

So yeah, trees do it a LOT cheaper (2% of the cost), but it requires active management and it’s not guaranteed to be on geological scale.

And I’m not aware of a scheme that enables this to happen. Are you?

If you build enough solar and wind to kick fossils off the grid, they’re going to overproduce at times of peak operation. Rather than wasting that peak production, use it to process CO2.

Also, Canada’s forests burned so hard, they were a net emitter this year. I’m not sure how reliable a carbon sink trees really are as the warming gets worse…

Sure is a shame there's so many scams related to that area. In theory, planting or protecting forests is one of the best things we can do. But in practice? A lot of organizations that claim to protect some area from industrialization are actually protecting an area that was never at risk in the first place. That is, if they didn't exist, the forest would be unchanged. Others are only protected for short periods of time. https://youtu.be/AW3gaelBypY?si=56uG8zf1iAeJM31H

Well, they're using renewable energy to power it. The limestone looks like it's just constantly recycled, so it would be just the initial transport there. Their output is tanks of compressed carbon dioxide which is sent to a concrete maker, so it really depends on how far away the concrete maker is. There's a thing called industrial symbiosis, where manufacturers co-locate so that one factory's waste easily becomes the factory next door's input.

I think it’s the opposite. This paves the way to enforce companies to pay to remove the carbon they emit. If this can be profitable then there is room to invest on improvements making it more feasible at large scale.

bro im starting one of these companies

They paved paradise and put up a parking lot.

Ok Joni

Possible not, you need to maintain the growth conditions for the algae, that has some meaningful energy cost.

At the California plant, workers heat limestone to 1,650 degrees Fahrenheit in a kiln powered by renewable electricity. Carbon dioxide is released from the limestone and pumped into a storage tank.

The leftover calcium oxide, which looks like flour, is then doused with water and spread onto large trays, which are carried by robots onto tower-high racks and exposed to open air. Over three days, the white powder absorbs carbon dioxide and turns into limestone again. Then it’s back to the kiln and the cycle repeats.

“That’s the beauty of this, it’s just rocks on trays,” Mr. Samala, who co-founded Heirloom in 2020, said. The hard part, he added, was years of tweaking variables like particle size, tray spacing and moisture to speed up absorption.

The carbon dioxide still needs to be dealt with. In California, Heirloom works with CarbonCure, a company that mixes the gas into concrete, where it mineralizes and can no longer escape into the air. In future projects, Heirloom also plans to pump carbon dioxide into underground storage wells, burying it.

So they're using the "limestone -> quicklime -> slaked lime -> limestone" cycle. The kiln must be powered by renewables (otherwise the process is pointless), but it's a perfectly reasonable capture method.

Storage is slightly less straightforward. Concrete naturally absorbs carbon dioxide over decades, mixing carbon dioxide in during production is just accelerating the inevitable.

Additionally, the reason concrete can absorb carbon dioxide is that cement contains quicklime, which is mainly produced by... you guessed it, heating limestone to release the carbon dioxide! The concrete won't absorb more carbon dioxide than was released during its production, so making excess concrete is not a solution to CO2 capture. However, if the concrete was going to be produced anyway (and we produce a lot), I suppose it's slightly better to have it absorb carbon dioxide sooner rather than later.

Pumping carbon dioxide into underground storage wells a more scalable solution, provided that the local geology (olivine?) can absorb the carbon dioxide.

An alternative not discussed in the article is to reduce the carbon dioxide into various feedstock chemicals that we currently derive from fossil fuels. Again, this would need to be powered by renewables otherwise the process is pointless.

You might want to read the article more carefully.

At the California plant, workers heat limestone to 1,650 degrees Fahrenheit in a kiln powered by renewable electricity.

Direct-air carbon capture has its fair share of problems to overcome before it can become a practical solution, but any such process must obviously be powered by renewables. To do otherwise would be pointless.