Internationally renowned experts have highlighted that to avoid the most serious impacts of climate change we need to limit global warming to 2°C between now and 2100. This is no easy task; it means that global greenhouse gas (GHG) emissions need to be reduced by 40-70% by 2050 and that carbon neutrality (i.e. zero emissions) needs to be reached by the end of the century at the latest[sc:1].
This highlights the need to look beyond emissions reduction to help us limit the amount of carbon that is available in our atmosphere. While governments should continue pursuing ambitious international binding agreements on tackling climate change – so far measures announced after the Paris Agreement would still mean temperatures increase by around 3°C[sc:2] – and making sure they are implemented, we need to think about other ways to mitigate climate change. And it is here that carbon sinks can play such an important role.
What are carbon sinks?
Carbon sinks absorb more carbon than they release acting like sponges that can soak up carbon compounds such as carbon dioxide[sc:3]. They are either a natural or artificial (man-made) reservoir that can store carbon for an indefinite period. The process through which carbon sinks can remove carbon dioxide from the atmosphere is called “carbon sequestration” [sc:3] whereas in climate negotiations, the reduction of carbon dioxide in the atmosphere achieved by carbon sinks is known as “negative emissions” [sc:4].
The main natural carbon sinks are our plants, the ocean and soil. As most of us will remember from our student years, plants use carbon dioxide which they find in the atmosphere for photosynthesis so that they can grow; some of this carbon is absorbed by the soil as plants die and decompose. Oceans are also a major carbon storage system for carbon dioxide as are other ecosystems such as the Antarctica. According to estimates of the Commonwealth Scientific and Industrial Research Organization, combined, the Earth’s land and ocean sinks absorb about half of all carbon dioxide emissions from human activities[sc:5]. Regionally, between 1990 and 2005 Europe’s forests absorbed around 10% of the region’s fossil-fuel emissions[sc:6].
So carbon sinks are undeniably an important resource when it comes to tackling climate change; indeed, most governments plan to limit temperature rises to well below 2°C and include actions to enhance carbon sinks.
But that is not the whole story: most natural carbon sinks, such as forests, can only temporarily store carbon.
Reasons to worry
The carbon will be released back into the atmosphere if the trees are burned down or when they decay while deforestation means that we are limiting what are some of our most important natural carbon sinks. In addition, excess carbon in the atmosphere as well as the impacts of climate change mean that a lot of the stored carbon might come to be released into the atmosphere. For instance, the rise in temperatures means that places such as Antarctica which are in permafrost will thaw and the trapped carbon dioxide will be released into the atmosphere compounding the issues we are facing.
There is also more worrying news, as it seems that our forests may not be able to cope with increased carbon in the atmosphere. Dutch scientists analysed trees in tropical rain forests and on the basis of their research, it appears that trees are not absorbing increased amounts of carbon. Tropical forests contain a quarter of all the carbon found on Earth, but while concentrations of carbon dioxide have increased, there has been no equivalent growth in trees which is what scientists expected given that photosynthesis relies on carbon dioxide[sc:7]. Similarly, it would appear that while previously Canadian forests were a carbon sink, they have now become a net source of greenhouse gas emissions[sc:8].
All this highlights two very important points which need to be taken into account by governments in our fight against climate change. First, we need to preserve and support our natural carbon sinks by eliminating deforestation and ensuring our oceans and ecosystems are healthy and can function effectively. Second, given recent scientific discoveries, it is clear that we cannot afford to rely on the important benefits of carbon sinks to get us to limit temperature rises to below 2°C. The above discounts the potential of artificial carbon sinks, such as artificial carbon-absorbing leaves, but as long as these are still in an early development stage, it is difficult to assess what their contribution may be towards mitigating the effects of climate change.