While biochar's effect on soils and plants is exciting, there are also great environmental benefits to its manufacture and use, and these stem from its capacity to lock up carbon. Soil is naturally a carbon sink – it locks away carbon and prevents it from entering the atmosphere – but a chunk of our troublesome greenhouse gases arises from ploughing soil and releasing this carbon. Although normal composting and mulching takes carbon in the form of organic matter and puts it into the soil, this quickly breaks down as matter rots, and the carbon is released again. Every time we dig or disturb the soil we speed up this process. Peat mining is an extreme example of this: when we disturb peat bogs we release carbon that was locked away thousands of years ago. But at least 50 per cent of the carbon in any piece of waste turned into biochar becomes permanently stable.