Blue carbon pathways for climate mitigation: Known, emerging and unlikely

As interest in natural climate mitigation solutions continues to grow, there is an essential role for coastal and ocean ecosystems ("blue carbon") to play. To meet mitigation targets, however, it is crucial that human actions to protect or restore blue carbon sinks are based on solid science and actionable human management opportunities to increase sinks and reduce emissions from ecosystem loss. Here, we reaffirm the role of coastal wetlands in climate mitigation opportunities. We update the state of the science regarding existing blue carbon pathways and explore expanding the blue carbon opportunities to new systems. Specifically, we analyze new science for those blue carbon pathways we categorize as "emerging" (e.g., management interventions involving macroalgae - both cultivated and wild, tidal flats, and marine sediments) where human action may be able to increase these sinks, but we currently have insufficient information to ensure that their climate mitigation benefit is additional. We revisit those that are "non-actionable" (e.g., management interventions involving calcifying organisms and marine fauna) where the scientific evidence is clear that there is no mitigation benefit, or the science is too uncertain to claim that human action can definitively increase these carbon sinks. With limited funding for climate action, it is critical that efforts focus on projects with the most mitigation potential. Blue carbon management is only one piece in the climate mitigation challenge, but it is an important one. Continued scientific research and investment in developing policy pathways is warranted for these actionable and emerging systems. At the same time, the world must continue to work to decrease emissions rapidly, invest in other natural climate solutions, and scale renewable energy technologies.