2021-11-14

Carbon cycle

I am pretty sure I did cover this in school, but I did not quite appreciate how significant it is.

One if the things that always gets me is the EXACT amount of CO₂ pulled from the atmosphere by a plant for it to grow, that I then eat, is the exact amount of CO₂ I then breath out from burning it (unless I use some of that carbon to get fatter, then that is released when one day I am cremated or eaten by bacteria). And the O₂ that is made by the plant growing is also the EXACT amount I need to use to breath to burn that plant and consume it. OK some of that goes in to poop that is used (O₂) and released (CO₂) when that is digested by bacteria. But the CO₂ is the same. It goes around in circles. The circle is complete. It works.

The carbon cycle is all about how carbon moves around in the world. Wikipedia has this the cool image.

So how to stop climate change? - it is so so simple - stop burning old carbon (i.e. fossil fuels).

It is fine to grow trees, make wood, and burn that, the carbon goes round and round.

It is fine to grow food, eat it, and breath out, the carbon goes round and round.

AFAIK cows farting is an issue, as that carbon ends up as methane with has a bigger impact, but AFAIK for less time, and apparently the answer there is feeding the cows seaweed! But generally using carbon to grow food to feed and animal that we then eat and breath out is again OK, carbon goes round and round.

Don't get me wrong, loads of other issues, too many cars and not enough walking and cycling, all sorts, but just looking at climate change, it is all down to the carbon. We'll improve a lot of other stuff by fixing the climate change issues as a side effect!

Almost anything we do with "recently" captured carbon then going to the atmosphere matters not a jot. Pull carbon from atmosphere and release it a year later - not problem. What matters is all that old carbon in fossil fuels being burned. Unless we want an atmosphere that was around a few million years ago, we need to stop.

Even all the "indirect" stuff, like carbon cost of manufacturing and transport, only matter when those processes use fossil fuels directly or indirectly. Make those processes use electricity or hydrogen from green supplies (not from fossil fuels) and they all end up carbon neutral.

The one thing, and this really is the one thing, that matters, is burning old carbon. Stuff pulled from the atmosphere millions of years ago and stuffed in the ground. Burning fossil fuels. That is what matters. That is what needs to stop. It really is as simple as that!

Heck, even making fossil fuels in to plastic which we don't burn, is not an issue! What matters is old carbon going to the atmosphere - STOP IT!

5 comments:

  1. It is amazing/depressing how many people who should know better seem to not get this... constantly seeing people comparing quantities of CO2 with no consideration of what is coming from fossil fuels and what is coming from some part of the carbon cycle...

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  2. > But the CO₂ is the same.

    Up to a point, Lord Copper.

    The amount of carbon dioxide consumed by a plant to grow is way, way more than you need to exhale to digest it -- this is necessarily the case or you'd not have anything left to live on! (Though some plants are remarkably hard to digest and can take up to 80% of the energy you get back from digestion: most are more like a third, and cooking them knocks it a lot further down). We are helped here by the fact that there are a *lot* of plants and that photosynthesis is about a hundred times better at producing organic material than eating plants :)

    But even if this were not the case, there is a *lot* of slop in the carbon cycle, and none of it is remotely as balanced on an individual level as you seem to think. It's not even that well balanced on a larger scale. Megatons of carbon are lost to the cycle every year by virtue of "marine snow", shelled organisms falling to the abyssal plain and (tens of millions of years later) often being subducted into the mantle or at the very least locked into carbonate rocks. Massive amounts of CO2 are returned to the atmosphere by the weathering of carbonate rocks and (to a much lesser extent) by volcanic action. The system wavers and wobbles all over the place on megayear timescales, but so far has always come back to something liveable in the end: but there seems to be nothing guaranteeing this, nor anything guaranteeing disastrously wide wobbles (look up "snowball Earth", and note that we seem to have had several rounds of planetary snowball).

    In fact there's *so* much slop in the system that on geological timescales sloppy edge effects dominate (and will continue to do so unless our worse-than-end-Permian-catastrophe levels of gaseous CO2 production wreck everything). Consider that the young Earth had perhaps ten to fifty thousand times the atmospheric CO2 it has now, enough to make the atmosphere much much denser than it is now, and no oxygen. Where did it all go? It was split into oxygen and carbon (largely by the marine carbon cycle noted above), and the carbon locked into vast amounts of carbonate rock. Even after immense amounts of oxygen went to oxidising all the exposed continental rock and all the dissolved iron in the oceans, giving us banded iron formations kilometres thick, we *still* have 32,000 times as much oxygen in the atmosphere than we do CO2. Every last bit of that was likely once bound to CO2 in the atmosphere of the primordial Earth... and so was a lot more.

    That's a fairly large edge effect (it thinned the atmosphere by perhaps a factor of ten or more!) and proof that, in the very long run, the carbon cycle is more of a carbon cascade, taking CO2 out of the atmosphere and locking it in rock.

    What's more, things have to stay that way -- the Sun is getting hotter so we want ever less CO2 in the atmosphere. You might note that we already have almost none: the preindustrial average of 0.025% is more or less nil on this timescale. This is an extremely bad long-term problem because it means we have run out of breathing room: we can't take much more CO2 out and still have anything left for plants to live on, but if we *don't* take more out the Earth will grow hot enough to boil the oceans in about a billion years, which will rapidly turn the Earth into a second Venus since water vapour is a very strong greenhouse gas and a planetary ocean's worth is disastrous.

    This needs working on and nature won't fix it for us. A gravity tractor seems like the way to go, slowly and carefully widening the Earth's orbit by repeated not-all-that-close passes of moderately-sized asteroids to compensate for the warming Sun. This is actually quite easy to set up, but needs active maintenance over geological timespans, which isn't really something our current civilization is up to.)

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    Replies
    1. > This is an extremely bad long-term problem ... in about a billion years ... This needs working on

      I think that's stretching the definition of a "long term problem" beyond any reasonable limit. A billion years ago there weren't even animals, let alone anything resembling humans, so trying to speculate about what will be the major problems facing the human race in a billion years from now is entirely futile.

      I'm pretty sure that by then we will either have (1) wiped ourselves out through our own stupidity; (2) evolved into something completely different; or (3) colonised space to a degree that the Earth is little more than a historical artifact.

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  3. Some interesting insights from Jordan Peterson on COP26. https://www.youtube.com/watch?v=vgpca5VmQ48

    I heard someone joke that humans found their evolutionary niche in releasing locked up CO2 for the benefit of trees and vegetation. Now that we have almost served that purpose our use has come to an end and we're done.

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  4. Short time scale stuff does matte. When taken individually, a tree growing for 100 years and then decaying/burning is a short time scale and seems not to matter. But during the time when it is alive, the carbon is locked up rather than floating around in the atmosphere, and replacing that tree at the end of its life means the carbon will continue to be locked up indefinitely. Multiply that by millions of trees and that's a significant amount of carbon being locked up indefinitely.

    Also, in some environments (e.g. peat bogs, wetlands, etc.) the dead plants end up being buried instead of decaying, so the carbon an individual plant has absorbed really does get locked up for geological time scales.

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