Putting combustion into reverse

With a scientist’s eyes, you can practically see carbon cycling through the living environment. Looking at a tree, you realise that it grew from a small seedling and that all that mass had to come from somewhere. Half the weight (more or less) of a living tree is water, but the other half is almost entirely various carbon compounds – and virtually all of that carbon was pulled from the air as carbon dioxide. Burn the wood, and most of it goes right back.