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What is... (natural) carbon capture?

By Dru Haynes

15th May 2021

The term ‘carbon capture’ crops up on an almost daily basis but what does it mean and why is it so important?

First off, we need to know what ‘net zero’ is. Simply put, this means making sure that the amount of carbon we put into our atmosphere is no more than the amount we remove – a balance if you will. The IPPC (International Plant Protection Convention) Annual Report 2018 concluded that to achieve net-zero and limit global warming to 1.5oC, then carbon capture is required especially as we continue to use fossil fuels. At current levels however, the planet Earth is on course for a 3oC temperature rise by the beginning of 2100. This will have a catastrophic effect on our natural world - melting ice caps, rising global sea levels, extreme weather, and the extinction of entire species as the balance of the planet’s ecosystem is disrupted. A serious issue indeed but what can we do?

Well, that’s where carbon capture comes in. Carbon capture involves isolating carbon dioxide (CO2) at its emission source, transporting it to a storage location, usually deep underground, and storing it. There are several ways it can be done – post-combustion capture (CO2 is grabbed after the fossil fuel is burnt), pre-combustion capture (CO2 is trapped before the fossil fuel is burnt and collected before it's diluted by other gases), and oxyfuel combustion capture (fossil fuels are burnt in oxygen resulting in a mixture of steam and CO2 which can then be separated). Once captured, the CO2 can be transported via a pipeline to be stored underground or recycled by converting it into plastics, concrete, or biofuel.

So what’s natural carbon capture then? Natural carbon capture is a process that has been occurring for much of the Earth’s history! Natural sources of carbon dioxide (including the respiration of animals, plants, volcanic eruptions etc) were naturally kept in balance by carbon sinks – ecological systems which collect and store CO2 – mainly plants, soil, and oceans. Plants use CO2 for photosynthesis, some of this is also transferred to soil as the plants die and decompose. Peatlands are historic sinks of carbon due again to the photosynthesising plant life they support - peatland environments are the UK’s largest store of carbon, equivalent to 8 years of total UK carbon emissions. Our oceans are another major storage system – marine plants and animals use the gas for photosynthesis, while some simply dissolve in the seawater.

Seagrass is just one example of our amazing (and local) ecosystems. Responsible for 15% of the ocean’s total carbon absorption, seagrass takes carbon from the water to build leaves and roots. As the plants die and are replaced by new shoots and leaves, the dead material collects on the seafloor along with other organic matter from dead organisms. This build-up of material forms layers of sediment which, if left undisturbed, can store carbon in the seafloor for thousands of years. Even further, when growing, seagrass roots anchor in the mud or sand, which in turn strengthens the seabed and prevents erosion making it one of the most important natural solutions to climate change.

Natural land and ocean sinks absorb about half of all CO2 emissions from human activities. However, we are now producing carbon emissions at a much faster rate than natural sinks can absorb. In conjunction with this, we have destroyed many of the world’s natural ecosystems - many of the world’s forests, one of the Earth’s primary carbon sinks, have now been deforested or are being deforested at an alarming rate. Now is the time to re-examine our relationship with our world, we need to come together to solve one of the greatest challenges to our planet for our own survival.

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