Earlier we unpacked the phrase "carbon neutrality." Yet a question probably lingers — what is carbon, that the whole world should wrestle with this one element? Today we go a little deeper. Not harder, only deeper. And the story begins with four hands.
The element with four hands
Everything in the world is made of elements, and elements join hands to form matter. But each element has a fixed number of hands. Hydrogen has one, oxygen two, nitrogen three. And carbon has four.
One extra hand may not sound like much. But four hands mean two things: that a single atom can hold up to four others, and that carbon atoms can hold hands with each other. The second is decisive. Carbon links to itself in long chains, closed rings, spreading branches — without end.
Imagine a set of Lego bricks in which exactly one brick connects in every direction. With that one brick you could build anything. In fact, of all compounds known to us, more than 10 million are compounds of carbon — more than every other element combined.
A diamond and a pencil lead are the same thing
There is a curious flip side to carbon's freedom of assembly: with nothing but the same carbon atoms, a different arrangement makes an entirely different substance.
The material is identical. Stacked in layers, or woven into a net. That single difference makes one a pencil lead worth pennies and the other a gem worth a fortune per carat. Peel a single layer off graphite and you get graphene — a film one atom thick, and far tougher than steel. Charcoal, carbon nanotubes: all the same carbon.
Our bodies, too, are houses built of carbon
Life on Earth is called "carbon-based life." That is not a metaphor. Take the water out of a human body and about half of what remains, by weight, is carbon. Proteins are built on carbon chains; the carbohydrates in rice and bread are, by name, carbon and water; fats are long carbon chains. Even DNA, which carries our inheritance, is written along a carbon backbone.
Substances framed on carbon are called organic matter, and the study of them is organic chemistry. Wood belongs here, of course. The timber we work with is, in the end, carbon that a tree drew out of the air and hardened into a body.
Carbon does not vanish. It moves house.
From here the story runs straight into our work. Carbon does not disappear. It changes form and keeps circling the planet. It rests in four places.
- The air. Floating as carbon dioxide. The smallest of the four stores — and the one where the trouble shows.
- Living things and soil. Trees, animals, and what they leave behind. A standing tree is itself a store of carbon.
- The ocean. Dissolved in water, holding many tens of times what the air holds.
- Underground. Limestone, and coal and oil. By far the largest store — and the one sealed shut the longest.
The cycle turns like this. A tree breathes in carbon dioxide and gives out oxygen; we breathe that oxygen in to live. Meanwhile the carbon that plants have captured from the air the same way comes into our bodies through food, and leaves again as carbon dioxide with every breath out, returning to the air. When living things die, microbes break them down and return them to the air as well. But some of it never got broken down. Buried, it was pressed and cooked for hundreds of millions of years, and became coal, oil, and natural gas.
So why did carbon become the villain?
Carbon is not guilty. Neither is carbon dioxide. Carbon dioxide works as a blanket, holding in heat the Earth would otherwise send out to space — and that blanket is necessary. Without it the planet's average temperature would sit near minus 18 degrees, and we would not be here.
The trouble is how fast the blanket is thickening. Carbon that took hundreds of millions of years to be locked underground is being dug up and burned by us within 200 years. Before the industrial era the air held about 280 parts per million of carbon dioxide; it has now passed 420. Nowhere in the 800,000 years read out of ancient ice is there a rise at this speed.
So the problem, stated precisely, is not carbon but which store we take it from. Burning coal means opening a vault that has been sealed for 300 million years and moving its contents into the air. Once out, there is no practical way to put it back. The same holds for oil, for the natural gas so often called clean, and for the many alternative fuels now appearing under new names. They may release less when burned, but if that carbon came from the underground store, it is no different.
Burning wood is different. That carbon was in the air until recently; the tree only held it for a while as it grew. Burn it and it returns to where it came from. Plant again where you cut, and the new tree draws the same carbon back down. It moves between stores; it does not increase. This is what we called "recent carbon" in our first story.
One last thing that is easy to confuse
Carbon and carbon dioxide are not the same word. Carbon is a single element; carbon dioxide is that element with two oxygens attached. By weight, carbon dioxide is about 3.67 times carbon. So "one tonne of carbon" and "one tonne of CO₂" are quite different quantities. Mix the two when handling emissions or reductions and the numbers go wrong by more than a factor of three. Hence the habit of checking whether a report says tC or tCO₂.
Carbon has four hands, and so it can build anything: it is the frame of life and the substance of the energy we have used. If there is guilt, it lies not with carbon but with which store we draw it from. Using the store that circles between air and forest, rather than opening the one sealed underground — that, in one sentence, is what we do.