Carbon sinks and the limited extent that they can use used to reduce greenhouse gas emissions

I suppose that it is human nature to ignore a problem, and then when that problem can no longer be ignored, attempt to find a pain free solution to it. It is only after humans have no choice that they realise that there is no pain free solution and they are forced to act in ways where the consequences of their actions are undesirable, but the consequences of not acting are even more undesirable. So it is with climate change.

Everything living thing contains carbon and most living things return the carbon in their structures to the soil or to the sea when they die. Years ago some living things died and the carbon in their bodies was sequestrated deep in the earth, in the form of oil, coal and natural gas. As a result of this sequestration the climate of the earth became more temperate and was able to sustain more forms of life, and many forms of life developed and evolved.

One living thing has in the past two hundred years or so gone about putting the carbon locked into the earth back into the atmosphere. That life form is human. As a result humans putting carbon from the ground into the air many people fear that the climate will become less temperate, more violent and possibly becoming such that it cannot sustain the life on earth as we know it.

There are life processes that can sequestrate the carbon in the air and return it to the sea or the soil. The most significant processes are the rain forests and the oceans, which absorb more carbon than they emit. The rain forests and the oceans are carbon sinks, and very useful to humanity. Together the rainforests and oceans absorb around 50% of the carbon that humans create. We cannot increase the size of the oceans. We can increase the size of the rain forests but in fact we are reducing the size of the rain forests each year significantly, while humans are emitting more carbon into the atmosphere.

World vegetation is thought to contain around 600 petagrams of carbon but soils contain around four times that amount. Most of the vegetation containing high carbon levels is in the tropics, but most of the soils containing carbon are in the temperate and northern latitudes. Ploughing soils releases carbon.

We cannot rely in the oceans and the rain forests to sequestrate more than 50% of the carbon we emit, and that percentage will decrease as human emissions increase. Even a modest decrease in human emissions means that we will not solve the problem; if overall human emissions decreased by 80% the oceans and the rain forests could soak up the excess carbon over a period of time, provided that we do not cut down any more rain forests.

However, even if some individual countries that are large polluters actually reduce emissions by 80% other countries who are modest polluters will increase emissions, as they seek to improve their standards of like.

Under the terms of the Kyoto protocol countries can increase forestry and count the additional carbon absorbed as part of their own carbon emission reductions. This is nonsense for two reasons:-

1.    No one knows precisely how much carbon a new forest will absorb; the evidence is that higher carbon dioxide levels in the atmosphere create a short spurt of growth, after which trees grow normally and absorb the carbon, much as they have always done. Although theeere is considerable uncertainty in the field Kyoto assumes that all the calculations presently used are correct and viable.

2.    Increasing a carbon sink does not reduce emissions; at best it provides a small help in sequestration a small amount of emissions. We do not understand the permanence of a carbon sink in the soils; the matter is complicated further by human activity that will seek to crop the trees, which releases carbon back into the atmosphere, and then burn the trees and biomass, which releases even more back, all in the name of carbon neutrality.

Of course we should seek to improve and enhance the carbon sinks, by planting more trees and farming in ways that release less carbon and other green house gases and in ways that produce higher yields which can sequestrate more carbon, even in the short term. We need to understand the role that nitrogen based fertilisers play; these release nitrous oxide and ammonia into the atmosphere, while nitrogen is essential for healthy plant growth and its availability speeds up the creation of a carbon sink.

There is a lot that we can do to improve carbon sinks by stopping the cutting down of trees, improving forestry management and improving farming practices, but whichever way you do the mathematics, you will not be able to reduce carbon dioxide emissions by taking them out of the air and putting them in a sink by more than a relatively modest amount. Of course it should be done – the reduction may by “only” 20% over a twenty year time frame, and we need to use every means of reduction possible, but creating as many carbon sinks as we can while maintain land for food and for people to live will not solve the problem of emissions.

This is because as the climate warms so the capacity of a sink is reduced because the warmer climate creates more soil and plant respiration, which means greater sink emissions. In other words each sink has a capacity that it can hold and not exceed, and that capacity will reduce as the climate gets warmer.

Carbon sinks, planting of trees and all the rest of it are important, but they can no way offset carbon created by burning fossil fuel. We have to burn much much less.