Counting Cats in Zanzibar Rotating Header Image

Carbon

I’ve been slow posting because I’ve been enjoying the spectacle of Climategate, or CRUdgate, or whatever you want to call it. Things do seem to be calming down a little as we start to move from the denial-that-this-is-at-all-significant phase to the hold-an-enquiry-to-avoid-having-to-talk-about-it phase. Only when we move out of that into the-enquiry-exonerates-everyone stage can we expect a further burst of outrage. Given the complexity of some of the issues, that could be years away.

This earthquake does seem to have shifted the landscape quite considerably. Issues like motives that were previously subject only to speculation are now accessible. Cracks have been forming in the media facade – so far, ones that could be plastered over quite quickly if things turn around, but significant nevertheless. Several prominent and respected scientists have taken the opportunity to break ranks. And Google now returns 10 million results for the word “Climategate”. (Although their predictive text thing doesn’t seem to recognise the term. Although “ClimateGroundZero” does, with about 10 thousand hits. Anyone know what that’s about?)

So it occurred to me that I’d better get on and do some more posts on this climate stuff, before it all gets out of date!

One of the earliest Environmentalist catchphrases I remember from my youth was “lungs of the planet”, used to describe the rainforests. It sounded plausible. Everybody knew plants consumed carbon dioxide to produce oxygen. Fewer plants would mean less oxygen, right? That sounds bad. It was only much later that somebody told me about the carbon cycle, and that in particular, it meant that the rainforests did not in fact produce our oxygen. Or rather, they consumed approximately the same amount that they produced.

The carbon cycle is inextricably linked to the cycle of life, consumption, death, and decay. Plants process carbon dioxide to produce oxygen and vegetation. Animals, bacteria, fungi, etc. consume oxygen and vegetation to produce carbon dioxide. The two balance. The two must balance, in the long run, or eventually the animals will have eaten all the plants or the plants will have consumed all the CO2. And this balance tells us precisely where our oxygen comes from – at least in a carbon accountancy sense.

Our oxygen comes from agriculture, from the crops that we and our meat animals eat.

The rainforests, on the other hand, supply all the bugs and critters that eat rainforests. When trees die, the fungi eat them, returning the CO2 to the atmosphere. A forest that is neither growing nor shrinking produces no net oxygen. It produces no net carbon dioxide. It is carbon neutral. (Not quite true, but I’ll talk about that in a minute.) If you chop down the trees, the animals die too, and balance is restored.

So while it is true that the reason there is oxygen in the atmosphere is plant life (70% of it from algae), and that if you got rid of all plant life it would soon disappear, it isn’t true that if you reduce the plant life you reduce oxygen. Because by getting rid of the plants, there is no food for the animals, and they stop consuming the corresponding amount of oxygen. The oxygen level would stay the same. The forests are only the lungs of the forests.

And this all has an impact on the “carbon offset” debate. One of the ways they have proposed to absorb carbon dioxide is to plant more trees. And people are getting rich from offering this service. But of course this only lasts until the tree dies, at which point the carbon is all released back into the atmosphere. This is more like sweeping the carbon under the rug.

If you want to turn forests into real carbon sinks, you have to take their carbon out of circulation permanently. One way to do this is to burn them. If you burn wood in insufficient oxygen, it turns into charcoal which the bugs can’t eat. You then bury the charcoal. (Forest fires do that naturally.) There are other places where there is no oxygen that you could put dead trees – peat bogs or the bottom of the oceans, or down deep mine shafts. And there are other measures that can be taken to build up soil, which again happens naturally and can act as a more permanent carbon sink. This would work. But when you compare that to the coal mining industry, its folly becomes evident. You are simply reversing the mining process, and by doing both being extremely inefficient about it. You had might as well leave the coal where it is and use wood for fuel. And we already know that doesn’t work, because when we tried it prior to the industrial revolution, we ran out of wood.

Besides life, the other major component of the carbon cycle is the oceans, and in particular the solubility pump. There is a common perception that all the fossil CO2 humans have emitted is still up there in the atmosphere, which is untrue. This also has to do with the persistent claims in some sceptic circles that humans can’t be responsible for the build-up of CO2 because it doesn’t stay in the atmosphere that long. This is also untrue, and you’ll note that unlike most on the warmist side of the debate I have no issue in saying so.

The solubility of carbon dioxide in seawater changes radically with temperature. Cold water can dissolve a lot more CO2 than hot water. And on the Earth, water near the poles is a lot colder than it is at the equator. This results in a constant circulation of CO2 that utterly dwarfs what man can do. Every year, about 330 billion tons of carbon dioxide is released into the atmosphere from the tropical oceans, and about 330 billion tons of carbon dioxide is absorbed again at the poles. Humans are responsible for about 20 billion tons.

(A quick note about tons of carbon versus tons of carbon dioxide – CO2 contains a carbon atom weighing 12 units and two oxygen atoms weighing 16 apiece, so carbon dioxide is (12+16+16)/12 times heavier than the carbon it contains. Carbon cycle accountancy often uses tons of carbon, because it allows for all the different compounds that occur in the cycle. This has been known to cause confusion.)

So the net result of this gigantic flow through the atmosphere is that any individual carbon dioxide molecule is only likely to stay in the atmosphere for about five years. This figure has been measured by looking at the ratio of isotopes of carbon – there is a variety of carbon atom that doesn’t weigh 12 units, but 13. It’s rare, so it doesn’t have much effect on the overall numbers, but it can be used as a tracer to try to figure out where the carbon is coming from or going. Everyone who has done it comes up with figures around 5 to 10 years for the residency time.

This means that putting CO2 into the air is not like filling a bath. It is more like pouring water into a river. The water level still rises, but it is not a simple matter to say by how much, or what is responsible. It depends on the outflow and how it is affected by the increased level. And of course, there may be other things that affect it too. This is why in Al Gore’s big chart the CO2 levels rose and fell in line with the temperature, about 800 years delayed. Higher ocean temperatures release more CO2 and absorb less.

However, all of this is a lot less simple than it appears. How do you go about calculating how much CO2 the polar oceans absorb? Well, you have to measure their saturation with CO2 (varies from place to place), their temperature (varies a lot), the effect of currents, turbulence, sub-surface mixing, etc. (enormously complicated and poorly understood), the solubility curve (can be measured in the laboratory, but small errors are inevitable) and then sum that up over the area of the oceans, which is a huge number and a huge expanse to go out and survey. It would be very easy to miss something. You shouldn’t trust these numbers.

But of one thing there is no doubt, that in the long run the oceans have more than enough capacity to absorb all the CO2 we emit. The oceans naturally contain 50 times more carbon dioxide than the atmosphere. So when they reach equilibrium, the oceans will have absorbed 98% of the rise. Geologically speaking, it is a blip that is unlikely to even show up.

6 Comments

  1. El Draque says:

    You may be able to correct me here.
    I seem to remember reading that the CO2/oxygen cycle is not completely in balance.
    The output of oxygen was ever so slightly larger than the oxygen consumption, and that’s why the CO2 proportion in the atmosphere – I mean many millions of years ago – was reduced and the oxygen content increased steadily.
    Life then adapted to higher oxygen levels, lived at a higher intensity and turned it back to CO2 at a faster rate.
    Only now is it about in balance.

    Is that right or are my old memory banks finally fading?

  2. Plamus says:

    Another negative feedback loop mechanism: fires. If you get higher CO2 content in the atmosphere, you get fewer fires (from lightning strikes), which is conducive to more vegetation, hence, less CO2. IIRC, at atmospheric O2 content of about 28%, organic matter tends to combust spontaneously from static discharges. Personally, I would rather be forced to breathe (inhale/exhale) more frequently (or develop more lung surface) than ignite when a dry air mass hits my preferred habitat.

  3. Pa Annoyed says:

    El Draque,

    Both O2 and CO2 have changed radically over the past millions of years. On that time scale, the geological effects (which I haven’t mentioned) dominate over the effects of life or even the oceans. The current unusually low level of CO2, for example, is reckoned to be caused by India crashing into Asia, raising the Tibetan plateau, and its erosion sucking CO2 out of the atmosphere by chemical means. Change something by one part per billion per year for a hundred million years… and the atmosphere changes a lot faster than that. So in a sense, it’s not exactly in balance now either – no more than the Earth ever is – it depends how you look at it.

  4. Rob Fisher says:

    If warmer oceans mean the oceans can dissolve less CO2, could that be one of the feedback effects that warmists need? Warmer planet means oceans release more CO2, planet gets warmer still due to greenhouse effect…

    Perhaps that is the root of the explanation for CO2 change lagging temperature change by 800 years in ice core records and yet CO2 is still somehow the cause… Obviously there comes a point where adding more CO2 does not cause more greenhouse effect, so the feedback will not go on forever, but it sounds plausible as a feedback mechanism to me.

  5. Pa Annoyed says:

    Rob,

    Yes, it would act as a positive feedback. We know from the ice ages that a 10 C change in average temperature corresponds to a 50% rise in CO2, Meaning 1C (as predicted by the minimal CO2 greenhouse) would give on the order of 5% change in CO2. I suspect it’s non-linear, so that number may be a bit off, but I can’t be bothered to go look it up.

  6. Rob Fisher says:

    Yes, it doesn’t sound like a very exciting positive feedback when you put it like that.

Leave a Reply

%d bloggers like this: