Could we control our climate?
Could we control our climate?

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Could we control our climate?

4.3 Other possibilities

A further suggested method using the biosphere is to plant trees, then prevent them from decomposing by turning them into charcoal or biochar (Figure 12). This has a co-benefit of improving soil quality.

The technological equivalent uses artificial trees and other direct air capture (DAC) methods (Figure 12) to ‘scrub’ CO2 from the air with chemical methods; the CO2 can then be sequestered with CCS.

Figure 12 shows a photograph of 2 hands holding a pile of black charcoal pellets. Figure 12 shows a photograph of an array of large fans in a desert region making up a DAC plant. The arrays are stacked in long rows 4 high. A car is shown for scale, it's length is approximately twice the diameter of a fan.
Figure 12 Low-tech and high-tech methods of CDR. (a) A handful of biochar. (b) An example design of a DAC plant by Carbon Engineering.

Watch the video below to learn of some other suggested methods for carbon dioxide removal.

Download this video clip.Video player: Video 2 More proposed CDR methods
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Transcript: Video 2 More proposed CDR methods

Dr Tamsin Edwards
I want to talk a bit more about carbon dioxide removal, because I think people see this as quite an exciting area, and there's lots of interesting research going on. In terms of biological capture and storage, of course, people are thinking much more broadly than just planting trees. They're thinking about creating straw to bury in the soil, planting mangroves, salt marshes. These things can help.
Mangroves, for example, can help us sea defenses, so there's a co-benefit there. Using more trees and straw as building materials. So that again locks up the carbon without allowing it to decompose and escape into the atmosphere. And in the oceans, not just plankton, not just the kind of small-scale stuff, but higher life forms like seaweed as well.
And in terms of the chemical capture and storage, with the direct air capture with chemicals, it could be more efficient than a biological tree. An artificial tree could be more efficient, but it's not clear at the moment whether it would actually still be more expensive than not emitting the carbon in the first place. But obviously, that could change in the future.
And when you capture the CO2 and have to store it, if you hold it as a gas in a geological reservoir, you obviously have to think about how to prevent it from leaking again. Another possibility is to store it as a liquid under the sea. So pump it down to the bottom of the ocean, and then that will be trapped for hundreds of years, if not thousands.
But one really interesting area I saw recently in the news in 2016 was turning CO2 into rock. It's a very promising area, I think. In Iceland, there was a project called CarbFix, which wasn't about wanting some toast desperately. It was about fixing carbon by pumping CO2 dissolved in water into the basalt rocks underneath Iceland, underneath the ground in Iceland. And those rocks, unlike the kind of normal reservoirs where you pump oil out that we normally think of storing CO2, these basalt rocks contain calcium, magnesium, iron, and they're very active. So the CO2 reacts with the rock and forms carbonate minerals, like calcium carbonate that makes up limestone. So that was really an interesting project, because it worked a lot better than they expected. So I think that's one to watch out for in the future.
There are lots of kind of related chemical capture methods, mainly called enhanced weathering. So we think of weathering of rocks, silicate rocks, where rain, for example, will break down the rocks in combination with CO2. So you could crush silicate rocks, put it into the soil, into the oceans, and then that kind of accelerates the natural processes that breaks down, that break down rocks and helps to capture more of the CO2. And even you could treat the rain itself. So people have mentioned treating clouds to make rain more alkali, and then it is more likely to react with CO2, again, drawing it out of the atmosphere.
Now, one I heard just this week, which was really interesting and kind of an unusual, creative idea was not taking CO2 out of the atmosphere with plants, or with chemical methods, but just with simple freezing, physical methods. So if we had a low enough temperature, the CO2 just simply freezes into a solid out of the air. And so where would you go to do that? Well, Antarctica. The average temperature in the interior is about minus 57 degrees centigrade.
It can go down to about minus 90. And you only need to go about another 50 degrees or so only, or maybe less if it's under high pressure, and actually the CO2 will just freeze out. And that's actually just the same as on Mars, where the temperatures are very cold, and the ice caps you see on Mars are not water, of course. They're made of CO2. So really, you'd be sort of creating these CO2 Mars ice caps, but within Antarctica to lock up that CO2 as a solid, and then you could store it in the usual way.
So different ideas do go in and out of fashion in a way. People think of these immensely creative ideas, and then things change as the science gets explored more, in more detail, the kind of effectiveness, and how well it scales up. All these things get explored. And sometimes they are found to be, of course, less promising than first thought. But I think it's fascinating because it shows such creativity the ways that we think about capturing CO2 out of the atmosphere and locking it up for the long term.
End transcript: Video 2 More proposed CDR methods
Video 2 More proposed CDR methods
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