I am not optimistic about using electrically powered machines to pull CO₂ from the air. Using plants seems more efficient and scalable, and the plants automatically turn the CO₂ into carbon-rich solid materials.

But James Salzman has been telling me for years that *if* you want to use machines, it's better to use them to pull CO₂ out of water than out of the air. The CO₂ concentration in seawater is 1000 times higher than in air, and a lot of chemical reactions work better in aqueous solution!

But it's still nontrivial.

Now folks at MIT have developed a method of pulling CO₂ out of the water that takes 0.77 MWh of energy per tonne. This is about 1/3 as much as typical methods of pulling it out of the air:

https://medium.com/predict/mit-may-have-just-developed-the-ultimate-climate-technology-37c10791e69b

The actual paper is here:

https://pubs.rsc.org/en/Content/ArticleLanding/2023/EE/D2EE03804H

It's better than previous methods. Electrodes put protons into seawater fed to the cells, making the water acidic and converting dissolved bicarbonates into gaseous CO₂. Then the water is fed to a second set of cells with a reversed voltage, to recover the protons and reduce the water's acidity.

But I'm still not convinced that this is better than using plants - self-reproducing solar-powered technology, which doesn't just grab CO₂ but actually converts it into carbohydrates.

Plants may be the ultimate climate technology.

@johncarlosbaez Does removing a given amount of CO₂ from the oceans produce the same long-term effects as removing the same amount from the air?

@gjm @johncarlosbaez Since the 1800s, we have burned about a trillion barrels of oil at ever increasing rates. (Not to mention coal and natural gas.) How can we expect technology to undo that?

@georgebeck - "How can we expect technology to undo that?" I doubt any technology that requires electric power to extract the CO₂ will scale up well enough to do anything useful anytime soon. We can dream of a future where electric power is so cheap that we're willing to spend it on undoing the damage we created earlier. But right now the only technologies that exist at the necessary scale and don't require electric power let *plants* do the work of sucking CO₂ from the air. They are evolved to do this, and they mainly need sunlight and water to get the job done.

But of course we urgently need to stop burning carbon! That is the first step.

@johncarlosbaez @georgebeck There's an intriguing startup betting on the idea that solar will scale (and costs will fall) fast enough that getting natural gas from the air will be cheaper than getting it from the ground: https://terraformindustries.wordpress.com/2023/01/09/terraform-industries-whitepaper-2-0/

Of course, this is only *capture*, not *sequestration*. (As long as there's still any "getting it from the ground" for it to displace, however, the net effect is equivalent.)