What a mess!

There has been a lot of talk of carbon capture recently since it appears we will not be able to slow down burning fossil fuels anytime soon.

So far humans have released 2500 billion tonnes of CO2 into the atmosphere since heavy industrialisation began. I just wanted to think a little bit about what it would mean to put that all away again.

Most serious plans for carbon sequestration involve pumping CO2 back into the earth. It is a semi-liquid at those higher pressures and so easier to store than at the surface, there is also a lot of space down there. But what if we were to transform CO2 into a solid and keep it at the surface?

First of all, trees do this all the time, approximately half the dry weight of a tree is carbon. A tree can absorb of the order of 20kg of CO2 per year and will store roughly a tonne over its lifetime. Once the tree dies all that carbon will be released back into the environment, so we would need to create greenery in places where it was absent to store more CO2. 

If we were to somehow terraform the whole of the Sahara into an Amazon-like forest, we would store roughly 700 billion tonnes of CO2. This is barely 30% of the total we have emitted. Of course, in reality the Amazon itself is in decline and almost 20% of it has already been lost. This has added an extra 50 billion tonnes of CO2 to the leger. 

Okay, let's get even more fanciful. What if we could somehow make a machine that could turn CO2 into diamond. If we were to build a pyramid out of the diamond blocks we produced, pharaoh style, how big would it be?

It would be a square pyramid of pure diamond to rival mount everest in size. It would have a base of roughly 10km and a height of about 8km. The tallest pyramid ever made by humans, still the great pyramid of Giza, is only 0.15 km tall. 

But diamonds seem a bit unrealistic right? What if we actually stored it as a more familiar form of carbon, pencil lead say (graphite). This has a lower density and so we will need to store a little more of it by volume.

If we were to store all the CO2 we have emitted as graphite blocks, we would cover the whole of Britain to a height of 5 feet!