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Challenge CARBON - how do we fix enough carbon to cool the climate?

picture from National Geographic, here.


We have a global problem with carbon dioxide - 4.1 billion metric tonnes a year more are being released into the atmosphere than current systems can absorb. We need to cut down, and there are lots of schemes underway for that including 10:10 - cut your carbon 10% in 2010! - but we also need to fix the mess.


Your challenge - design a solution that will absorb 4.1 billion tonnes of carbon dioxide a year without further endangering global food supplies. Ideally the carbon will be fixed into the geological cycle - as rock or on the sea floor.

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My solution would be to encourage growth of plantlife. Forests can be planted on the edges of deserts to combat ongoing desertification, or in friendlier climates to support a sustainable logging industry, and algae can be bred at artificially-created pools of sea-water to create a source of nutrition or even energy.

Our planet already has an effective system for getting rid of excess carbon dioxide. Let's tweak it and make the best of it!
OK Alon - show me the numbers - how many of what kind of plants? Where, which areas? Where will the water come from? How much land area will be needed to fix this amount of carbon a year?
After searching, this is the closest I found to a definitive answer.

"It is estimated that a 3 acre algae farm will consume up to 54,000 metric tons of carbon dioxide and produce 29 metric tons of biomass per year." (http://www.algaecake.com/about.html)

Now, this is a very optimistic evaluation by an R&D firm desperate for investments. I would say it assumes plentiful access to sunlight and nutrient, and optimized species of algae. It also assumes that the CO2 consumed is produced on the spot rather than consumed from the atmosphere.

Let's cut this number in half: 27000 metric tons per 3 acres.

Unless I'm mistaken, a quick calculation shows we will need about 152,000 acres, which are about 615,000 square kilometers. This is about one quarter of the Gobi desert, or the states of California and Arizona combined. Not a small tract of land, to be sure - but when equally distributed around the globe, it shouldn't cause too much of a strain. It would be a gigantic and very expensive engineering project, but ultimately a beneficial one considering the advantage of algae farming.

And this is from algae alone; we can reduce the amount of algae farm by supporting forestation and re-forestaion efforts.

Sadly, the most promising Algae Farming R&D firm, Green Fuels, was a victim of the credit crunch. This goes to show how ecologically important research should not be left to the whims of market forces.
Nice work Alon - hope the mods can give you some power points - a few more questions

- where does it say about the CO2 being produced on the spot?

- what will happen to the algae after they have fixed the CO2? How does the fixed CO2 in the algae get into the geological cycle, ie out of atmospheric circulation?

- business planning - how could CO2-fixing algae farms be paid for? What kind of cost are we looking for per metric tonne of CO2 fixed, for example? Could it be sold as a large-scale offsetting project (assuming there's a mechanism to fix it to geology!)
Alice M Yaxley said:
where does it say about the CO2 being produced on the spot?

This is implied at most articles dealing with carbon-absorption through algae. Here, for example, or here. From what I gather, the carbon dioxide emitted by the power plant is supposed to dissolve in the water for optimal absorption.

Alice M Yaxley said:
what will happen to the algae after they have fixed the CO2? How does the fixed CO2 in the algae get into the geological cycle, ie out of atmospheric circulation?

The algae absorbs the CO2 and creates an oily substance which can be harvested and used as fuel. Alternatively, it can be harvested for proteins to be used as fodder for fish and livestock, or maybe even as nutrition supplement for humans. In other words, I don't know what happens to it in the geological cycle. I would wager that if it is burned as fuel, it releases CO2 to the atmosphere. What happens when it's used as food? again, I don't know; you're the biologist - what does happen to digested CO2?

Alice M Yaxley said:
how could CO2-fixing algae farms be paid for? What kind of cost are we looking for per metric tonne of CO2 fixed, for example? Could it be sold as a large-scale offsetting project (assuming there's a mechanism to fix it to geology!)
Sadly, I can't give you any concrete numbers on this one. I do, however, believe that algae is notoriously easy to grow. The main costs of such a project would come from actually digging 150,000 acres of seawater reservoirs. I don't know of any comparable projects (the Suez and Panama canals were dug at a difficult terrain in order to reach from point A to point B and not in order to fill a large enclosed area with seawater, so they're not a good case for comparison IMO).
Biodiesel or algae-based nutrition may take a very long while to return the costs, but it is a nice benefit nonetheless. Since we're talking about digging huge tracts of land, which are bound to be on someone's national territory, such a project is bound to be undertaken by national and international agencies rather than by business ventures, so short-term profitability should not be an issue.


For information on alternative solutions, you might want to check this wikipedia article, though I still believe that plantlife-based carbon sinks are the most beneficial solution in the long run.
This is implied at most articles dealing with carbon-absorption through algae. Here, for example, or here. From what I gather, the carbon dioxide emitted by the power plant is supposed to dissolve in the water for optimal absorption.


OK - so the carbon costs of setting this up need to be subtracted from the net carbon fixed. Please will you find an estimate and adjust your calculations of how much acreage of algae tanks we need?



The algae absorbs the CO2 and creates an oily substance which can be harvested and used as fuel. Alternatively, it can be harvested for proteins to be used as fodder for fish and livestock, or maybe even as nutrition supplement for humans. In other words, I don't know what happens to it in the geological cycle. I would wager that if it is burned as fuel, it releases CO2 to the atmosphere. What happens when it's used as food? again, I don't know; you're the biologist - what does happen to digested CO2?


Ah yes - if it is burned as fuel or digested as food the CO2 is released into the atmosphere again - no use for reducing atmospheric CO2! We need to look at ways to turn it into rock - sink it in the ocean, for example, if we can be sure that CO2 won't escape through biological processes as it sinks.

Sadly, I can't give you any concrete numbers on this one. I do, however, believe that algae is notoriously easy to grow. The main costs of such a project would come from actually digging 150,000 acres of seawater reservoirs. I don't know of any comparable projects (the Suez and Panama canals were dug at a difficult terrain in order to reach from point A to point B and not in order to fill a large enclosed area with seawater, so they're not a good case for comparison IMO).
Biodiesel or algae-based nutrition may take a very long while to return the costs, but it is a nice benefit nonetheless. Since we're talking about digging huge tracts of land, which are bound to be on someone's national territory, such a project is bound to be undertaken by national and international agencies rather than by business ventures, so short-term profitability should not be an issue.

I don't agree - I think it is worth designing social enterprise models to get done what needs doing. Every venture needs paying for somehow and if we can point it at the target market - people who want to emit more CO2 than their fair share for now? - then it's sensible to see if it can be made to run in market terms.

For information on alternative solutions, you might want to check this wikipedia article, though I still believe that plantlife-based carbon sinks are the most beneficial solution in the long run.
Thanks, I will have a read. (Thanks so much for having a go at this problem with me, as well! I was stuck on the first question.)
While I still dream of a day when all cows would be given anti-flatuence pills like those one might eat before having beans, I think I will put my money on biochar.

As appealing as the idea is to fix carbon in the ocean's depths, it seems like one of the many big geo-engineering notions that will be big, complicated, and controversial. Biochar (ground up charcoal) has a number advantages. The technology is simple though improvements in stove designs get improved amounts of carbon sequestration so that you could design systems that serve everyone from rural, developing country smallhold farmers to developed world municipalities. In making the switch in developing countries to stoves like World Stove, you'd see side benefits for reduced soot and improved pulmonary health as a result. Used amendment (provided the early studies get supported by additional confirming research), the biochar will not only sequester carbon, but it will improve soil fertility and organic matter in the soil making this a benefit to farmers and encouraging its use.

Work is ongoing about the most desirable amounts of biochar per acre for given crops and to what extent the biomass used to make it (rice stalks, nut shells, etc., etc.) matter in the end result. While it is still in its early days, the idea has been generating interest and excitement as awareness grows. It is one to watch and an essential and relatively achievable approach to carbon capture.
Ah yes, thanks for weighing in - I have heard about these charcoal initiatives. I remember thinking it sounded like a miracle cure discourse. It could be really exciting. Do you have any numbers on the mass of carbon fixed and how stable it is? Is there spare capacity to grow the biomass to make the charcoal sustainably without further endangering food supply? I notice that you've named sources which are genuine byproducts of food plants, that it very sensible.

That reminds me that earthworm farming is genuine carbon fixing as well - earthworms fix atmospheric carbon into little rock crystals, which has been demonstrated to be from the atmosphere. If we could grow enough earthworms we would not only be able to fix a lot of carbon but we'd be making cultivation medium at the same time. Anyone going to help me with the numbers on how many earthworms would be necessary to fix 4 B metric tonnes of carbon a year?

Abstract: "Since they were first described in 1829, earthworm
calciferous glands have intrigued invertebrate anatomists and
physiologists alike. These organs are present in all species of the
family Lumbricidae, occurring in a range of morphological forms. A
common feature of the glands is that constituent secretory cells produce
a concentrated suspension of calcium carbonate. A number of possible
biological roles have been suggested for the secretion (i.e. egg
formation, pH buffering of the blood and ingested food, excretion and
respiration) but the true function has not yet been demonstrated
satisfactorily. Here, we investigated the putative respiratory function
of these organs by exposing the worms to 13C-labelled CO2 and glucose
and measuring tracer incorporation into the body wall, the gland tissues
and the calcareous secretion. Our results support the view that these
organs provide a mechanism of CO2 regulation in their tissues and that
both environmental and metabolic CO2 can be fixed in this way.
"

from here via here
According to the International Biochar Iniative, you could sustainably capture 2.2 gigatons of carbon per year by 2050 using agricultural waste. Based on terra preta in the Amazon, biochar is believed to be stable in the soil for hundreds if not thousands of years. This is admittedly speculative, but unlike a giant solar shade at a Lagrange point, it isn't rocket science.

It doesn't get you all the way to 4.1, but it would be a huge chunk of it and it is one of the few approaches that I remain optimistic about.
That's definitely a good start.

(Fixing into ocean depths doesn't have to be heroic engineering btw - it just has to be something non-harmful that will sink!)
True, though I've heard it described in conjunction with coastal fossil fuel plants which is a substantial step up in infrastructure and design. Both would be good and a wh*** lot more.

Starling said:
That's definitely a good start.

(Fixing into ocean depths doesn't have to be heroic engineering btw - it just has to be something non-harmful that will sink!)

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