The human race has been emitting carbon at an extreme rate for several centuries. Before we started burning things for the energy locked up inside them, the worlds carbon sinks and its carbon taps were in relatively stable harmony. For long periods of the earths existence, carbon absorbed by plants equalled the carbon emitted by breathing and volcano eruptions among other sources.
There are a variety of other carbon sinks. The earths oceans absorb carbon, while they can absorb huge quantities of carbon, this acidifies the water, which means that we dont want to rely on that to to great an impact.
Generally, the more carbon in the air, the more plants will grow. It was thought, until recently , that soil would also continue to increase its carbon sequestering as the quantities increase. Unfortunately, tests carried out worldwide have shown that this is not likely to be the case.
A study based on over 100 experiments found the opposite. When plant growth increases, soil carbon does not. Given the level of carbon stored in soil is thought to be around 3 times that of the total in plants, this could be of significant issue. The other advantage, is that soil carbon might be locked up for centuries or even millennia, plant carbon is just locked up for the lifetime of the plant.
By looking at old plants, it is thought that the biomass of plants growing in forests has increased by significant amounts (as much as 50%) but the amount of carbon in the soil has not had a similar increase. One reason for this, could be the fact that twice the biomass requires twice the nutrients from the soil, so any extra carbon is being taken up by the trees.
This is perhaps the strongest warning to us, about planting forests where grasslands have naturally grown – it may not help at all.
Experts were keen to point out, it does not matter if the carbon is in the soil or the plants growing in the soil, the level between the two appears to remain pretty constant.
One thing that we can be certain of, is that we have little full idea how much of our waste carbon will be absorbed, where and by what. Carbon capture and burying the carbon for millions of years is one method. The first and most important though, is to cut our carbon emissions as low as it is possible, any other methods can only take over then