Blue carbon is the carbon dioxide removed from the atmosphere by coastal and marine habitats. Vegetated coastal habitats, particularly saltmarsh and seagrass, have the capacity to store and sequester considerable amounts of carbon through photosynthesis and subsequent burial in soils and sediments, as well as trapping and storing carbon transported from terrestrial and other marine habitats. When undisturbed, some marine and coastal habitats have the capacity to store carbon long-term.
Natural England have published a report on Carbon Storage and Sequestration by Habitat 2021 (NERR094) which includes detailed information on marine and coastal habitats. It notes that saltmarshes are large carbon stores, although they are subject to erosion and accretion through natural coastal processes, and are affected by rising sea levels. Sea grass meadows also have the potential to store large quantities of carbon within the sediments if undisturbed. Their vegetation can also sequester significant amounts of carbon in situ, as well as acting to trap and store carbon released from elsewhere. There are significant evidence gaps in our understanding of carbon cycling for many marine and coastal habitats. However, the protection and re-establishment of coastal habitats will also provide climate change adaptation benefits in addition to those for mitigation.
This report also notes that coastal and marine habitats are receiving increasing attention due to their potential to store and sequester large quantities of carbon. The coastal and marine contribution to the global anthropogenic carbon dioxide budget is now recognised and reported by the Intergovernmental Panel on Climate Change (IPCC) and other international bodies, highlighting the increasing importance of these ecosystems in mitigating against climate change. However, in comparison to terrestrial systems, the role of coastal and marine habitats as a source and sink of greenhouse gases is comparatively under-studied.
In 2021, the Environment Agency have published a report that reviews the evidence behind carbon offsetting looking at a wide range of different offsetting approaches which could be used in the UK. See: Achieving net zero - a review of the evidence behind carbon offsetting - summary. An infographic summarises the findings for the public.