Governments and industry are looking for ways to use blue carbon ecosystems – mangrove swamps, salt marshes and seagrass meadows, rich in organic CO2 – to offset their harmful emissions. However, a recent Frontiers research, co-authored by scientists Phillip Williamson and Jean-Pierre Gattuso, said blue carbon habitats have “uncertain and unreliable” climate benefits.
The two researchers stated that it is unclear whether restoring coastal habitats can help negate climate change effects and that the scale of the emissions-mitigation effect of such ecosystems is likely to be overstated. The Frontiers analysis also said it is difficult to calculate the carbon offsets that restoration work could bring in the next 50 to 100 years.
Estimates of the rate at which coastal carbon ecosystems can remove carbon are complicated and vary greatly. Additional measurements are needed to achieve credible carbon accounting, but they will require time and effort that will bring up the costs of ecosystem restoration.
In addition, the net effects of such actions are still unclear. For example, flooding a coastal area to create a salt marsh could help accumulate CO2 but at the same time may release more greenhouse gases, leaving no real climate benefit at the end.
The two researchers also question whether coastal habitats will be able to withstand climate change effects such as storms, rising temperatures and sea levels, as well as human activity such as agriculture or tourism.
In an article for The Conversation, Williamson and Gattuso argue that “every effort should still be made to halt, and wherever possible reverse, the worldwide loss of coastal vegetation,” as blue carbon habitats “protect communities from storms, nurture biodiversity and species targeted by fisheries, and improve water quality.” If critical temperature thresholds are exceeded, blue carbon habitats may not survive, and previously stored CO2 may be released into the atmosphere.
The two researchers conclude that, given the questionable carbon removal and storage effects of blue carbon habitats, climate efforts should focus on “only using carbon removal methods to help achieve net zero where we are confident that they will work.”