Natural carbon sinks work by the absorption of carbon dioxide by the oceans via physicochemical and biological process or via photosynthesis by terrestrial plants. Therefor natural carbon sinks include forests and vegetation, soil, atmosphere and oceans. Carbon moves between them in a continuous cycle. Land-use changes and burning fossil fuels such as coal and oil are major sources of carbon. Coal contributes the largest share of CO2. In the last ten years, China has overtaking other regions such as the US and the EU and is now the largest emitter. This is a cool world view map from the global carbon atlas shows exactly where most carbon emission are emitted. Still, when considering the amount of emission per capita, the US is still leading by a fair margin. Farming is also contributing a lot as a carbon source – improvements in farming practices could help to reverse this.
Since 1870 human carbon emissions have ended up in the atmosphere (41%), land sinks (31%) and ocean sinks (28%). In fact, carbon sinks’ increased carbon absorption has kept the global average concentration to 393 parts per million (ppm) for 2012; otherwise we may already have reached a concentration at around 550 ppm.
While the Kyoto Protocol suggested that the absorption of carbon dioxide by trees and the soil is just as valid a means to achieve emission reduction commitments (carbon offset) as cutting carbon dioxide emissions from fossil fuels, there are also critiques of this approach. Their concerns include that forests’ ability to (temporarily) sinks carbon is being used to justify continued fossil fuel use. Also, especially afforestation in northern tundra regions may actually accelerate global warming since it reduces the the albedo effect. Dark green forests absorb more sunlight than tundra or farmland, adding to the warming trend if large non-forested areas that are now covered in highly reflective snow were planted with trees. Furthermore, it is impossible to accurately measure the sink effect of a forest.
Other artificial carbon sequestration methods include carbon capture and storage, geo-sequestration or mineral sequestration.
Carbon sinks are an important factor in how we deal with climate change mitigation – but we must not fall into a trap where sinks are seen as a way that can even out our increasing emissions. We must cut down, quite dramatically, on man-made carbon sources. Then carbon sinks can support our shift towards a low-carbon future.