For more than six days Earth has been our friend in the lunar skies. That fragile piece of blue with its ancient rafts of life will continue to be man's home as he journeys ever farther in the solar system. Apollo 17, December 14, 1972

Thursday, March 27, 2008

5. The Carbon Cycle - the three spheres

Three spheres....
This diagram is split into three sections: the subterranean, the biosphere and the atmosphere. At this stage in the explanation, we can ignore the subterranean but we will return to it. The atmosphere extends 50 miles above the earth's surface - travellers beyond that limit are described by NASA as officially astronauts! The biosphere is minute in comparison and extends about 100 metres into the atmosphere and a few metres down into the subterranean. It is like a thin film spread across the surface of the earth and is immensely complex and extremely delicate. It is in constant movement supporting life from the scale of a single celled organism to a complex creature with 30 trillion cells, immeasurable numbers of which colonise this thin space. A curious 'world order' has kept this inconceivably complex layer of life reasonably harmonious.

The role of carbon....
Absolutely intrinsic to life is the element carbon - it provides the structure and energy for virtually every living thing. For life to exist in this particular place in the universe it is the only element in the periodic table capable of doing the job.

The role of the carbon cycle....
The diagram is describing the equilibrium between atmospheric carbon dioxide and 'fixed carbon' in the biosphere - these two forms of carbon are in constant exchange. The cycle turns anticlockwise. As living beings, and occupiers of the biosphere we, along with virtually every other form of life, emit CO2 every time we breathe - this is depicted on the right handside of the diagram. CO2 remains in the atmosphere until plant life ensnares it during the process of photosynthesis, which with the aid of sunlight, chlorophyll and water, turns it into energy-rich carbohydrate and pure oxygen. The oxygen is returned to the atmosphere and the carbohydrate enters the food chain to support virtually all living beings. This is depicted by the left hand side of the diagram. As stated in an earlier post, the carbon cycle is life's provider. Not only does it provide us all with nutriment it also restore the oxygen consumed in respiration to the atmosphere - within certain limits it maintains an equilibrium. In other words if one side of the cycle produces more CO2, then the other side will be induced to work harder to restore the balance. There are also large 'sinks' by which any ups and downs on either side of the cycle will be smoothed out - in much the same way a set of shock absorbers dampen the springiness of a car's springs.

The physical effect of CO2 in the atmosphere....
Unlike nitrogen and oxygen there is relatively little CO2 in the atmosphere - only every 2500th particle in the air is a CO2 molecule, and yet it has a major effect on our existence. Without it the planet would be uninhabitably cold, and in overdose it would be impossibly hot, like Venus. It has greenhouse gas properties which allow light radiation through from the sun but absorbs and retains the 'warm' infrared radiation from the earth's surface.
When I was born in the 1950's there were even fewer CO2 molecules - about one in every 3300 particles. In the last 50 years the concentration of CO2 in the atmosphere has increased by 30% and this is having many different types of impact on the biosphere. Unlike the carbon cycle most of these impacts do not have compensating counterbalances, and so the situation is tending to run out of control. The delicate biosphere is getting disrupted and could soon be beyond any possibility of self repair.

The next post will examine what is causing this rise in CO2.

(The chemists will have spotted a deliberate mistake on the slide - CxHy is not the generic formula for a carbohydrate. but bear with me, you'll see why I used it on the next post)


Anonymous said...

Hi Jeremy

This is a most impressive site.

A silly query to start with: I read this morning that the Wilkins(?) Ice Shelf is crumbling at a much higher rate than previously anticipated. From memory, I think it was said that it is now thought that the whole shelf may have gone by 2020 rather than 2050. At the same time, the article stated that temperatures at the South Pole were falling. I believe I also read last year that, whilst Ice in the Arctic was melting rapidly in Summer months, the water was freezing again to such an extent that the amount of ice actually increased rather than decreased. Many apologies if I have misrepresented what I read (either today or last year). However, my initial query is simple this: if these facts are correct, is there a scientific explanation for them? I have an intuitive (or perhaps I mean uneducated) suspicion that if ice melts and refreezes there is going to be some sort of "momentum effect" which would lead to more ice when the temperature falls again.

On a more general note, whilst I am becoming ever more interested in matters of economic significance, I have generally had very little interest in the climate change debate. I have never felt compelled to understand it in depth let alone actually (perish the thought) try to do anything about it. I am somewhat ashamed to admit that I have not even seen the Al Gore film (although, was it not thought to exaggerate things somewhat?).

When I have ever entertained the question of what lies behind my indifference, I have assumed that the reason was a somewhat British pessimism which presupposes that fossil fuels are going to continue to be burnt for at least several decades to come until they either run out or some clever inventions make such a thing entirely obsolete (irrespective of any climate change imperative). However, I am not so sure this represents my true view. I suspect that I have just not connected with the subject either emotionally or intellectually. I fear that the subliminal thought process, is (put crudely) that climate change is not going to much effect on me and that the cost will be borne by others in just the same way as many of the non-climate change injustices cause a profound level of unhappiness to others. i.e. We read yesterday that hundreds of thousands of Zimbabwean children are orphans and have HIV. Is there any wonder that today we find it hard to empathise with a call to arms in respect of a problem which will most probably impact on other people in several decades time in ways that are perhaps hardly more appalling? And on the more intellectual side, I suspect that the belief is that eco-sustainability is an ideological no-brainer and that there are far more complex causes of behaviour and injustices to understand before bothering to engage too deeply with a debate about climate change.

None the less, your enthusiasm is admirable, and I wonder if you think that climate change could be seen as a wonderful opportunity for all those more drawn to other more immediate and current consequences of injustice to participate in something which could lead to a very real shift in thought?

Let me know what you think, and please do not hesitate to give me a hard time.

Jeremy said...

Dear Anonymous,

Thanks for the comments and compliment which are very gratefully received. I'm slightly gritting my teeth as I've crafted a complete response to you only to lose the lot: so this will be the shortened version, and probably all the better for it.
Taking your points in order:
1. Ice shelf. I'm researching that at the moment. It's complex and often counter intuitive. for example if polar ice cap recedes (ie the north gets warmer) but the gulf stream is affected, the UK may get colder.
2. Trying to be interested in everything - impossible. I get Amnesty International's magazine every month and hardly glance at it. I know I ought to. I feel we have to play to our strengths and enthusiasms: the latter can be infectious.
3. In the opening few posts on this blog I used the word daunting a lot. It’s big and involves so many disciplines. But making a start showed me a lot:
a) that I loved science although I’d forgotten I did and that I could remember quite a lot of the principle
b) 30 years of part time philosophy helps me put science in a broad context – it’s not an end in itself. The love of life in myself and others is
c) By asking dumb questions you can get fantastic answers
d) By remaining detached from so called knowledge the learning flow can continue – a tough one
e) Not many people I’ve come across in the field have a big picture and perhaps this is where my consultancy training can help
4. Bangladeshis could be about to lose their homeland through inundation due to sea levels rising, almost certainly caused by the West’s profligacy. This we can do something about, if we could come to understand how our current value system is taking us in a destructive direction.
Do please keep commenting, and subscribing to the blog is only one click away at the bottom of the home page. I've got posts coming up on your ice question and the values issue.

Anonymous said...

Anonymous and Jeremy

My thought is that the only way any one individual can make a difference is by getting together with others, which is what we are doing ...

Jeremy said...

Kevin and Annoymous,

That's absolutely right.
All I would add is that:
* mass interest comes by marketing hard so I'm gathering email address lists and I've put two widgets in to encourage people to post elsewhere and also email a friend
* the framework has helped me to understand where the least work can have the most influence.

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