The three great carbon sinks
A carbon sink is anything that absorbs more carbon from the atmosphere than it releases – for example plants, the ocean and soil.
Forests are typically carbon sinks, places that absorb more carbon than they release. They continually take carbon out of the atmosphere through the process of photosynthesis.
Around 25% of all CO2 emissions are absorbed by the ocean, making it one of the world’s largest ‘carbon sinks’. The ocean absorbs CO2 from the atmosphere because, as the atmospheric concentration of CO2 increases, more is dissolved in the surface water.
While the ability of the ocean to capture and store carbon has helped to slow the accumulation of atmospheric CO2 – and, hence, the pace of global warming – it has come at a cost. Increasing CO2 in the ocean alters the chemistry of seawater – an effect known as ocean acidification – which has negative impacts on marine life.
The worlds soils contain billions of tons of CO2. The more the soil is covered by vegetation, the richer it will be in organic material and therefore in carbon.
How to cut the carbon contained in the atmosphere
Cutting the global production of carbon is a target that is well understood in many countries. Protecting our great forests such as the Amazon is clearly vital, deforestation must be reversed. However, if we can increase by just 4 parts per thousand (0.4%) the quantity of carbon contained in soils, we can halt the annual increase in CO2 in the atmosphere. In short, we can achieve a carbon neutral position quicker if we improve the ability of the soil to store more carbon.
How can soils store more carbon?
The more soil is covered, the richer it will be in organic material and therefore in carbon. Until now, the fight against global warming has largely focused on the protection and restoration of forests. In addition to forests, we must encourage more plant cover in all its forms.
1. Never leave soil bear and work it less, for example by using no-till methods.
2. Introduce more intermediate crops, more row intercropping and more grass strips
3. Add to the hedges at field boundaries and develop agroforestry
4. Optimise pasture management – with longing grazing periods for example
5. Restore land in poor condition. E.g., the world’s arid and semi-arid areas
But decomposing waste produces CO2
All waste that decomposes lets off gasses. If it decomposes within an aerobic condition, ie in composting, it will let off CO2. If it decomposes in an anaerobic condition, it will let off methane, CH4. Anyone with a home compost heap is producing CO2 right now.
It is part of the natural carbon cycle that decomposition leads to carbon dioxide being produced.
Generally, only a certain amount of CO2 from composting will be emitted, the rest is locked into the humus as it mineralises and goes back to soil as organic carbon. Compost contains as much as 20-30% organic carbon. The carbon rich humus produced by composting provides for more fertile soils and soils that are better able to cope with the effects of climate change.
Practical steps for a UK householder
We can all make changes, and we can all start today
1. Grow more, and grow a wider range of plants
2. Start composting and recycling at home
3. Work with your community
4. Form gardening clubs at work
5. Influence and encourage friends and family
6. Swop and share ideas
Benefits of composting
- Enriches soil, helping retain moisture and suppress plant diseases and pests.
- Reduces the need for chemical fertilizers.
- Encourages the production of beneficial bacteria and fungi that break down organic matter to create humus, a rich nutrient-filled material.
- Reduces methane emissions from landfills and lowers your carbon footprint.