Blue carbon on the rise: challenges and opportunities

Abstract

Climate change is a global concern that requires urgent solutions. As a signatory to the Paris Agreement, China has committed to have its greenhouse gas emission reach a peak by the year 2030, which means that severe countermeasures for reducing emissions have to be put into practice. This is a hard mission given that development is still the top priority in the years to come for China. Under such circumstances, enhancing carbon sequestration becomes an effective approach to achieving the goal. While terrestrial green carbon sink is already in practice, the ocean carbon reservoir, containing 93% of global CO2, as 50 and 20 times the carbon inventories of atmosphere and land, respectively, has great potential to expand. Each year, at least 25% of the anthropogenic CO2 has been captured by marine ecosystems as blue carbon [1]. In 2009, the United Nations Environment Programme (UNEP), the Food and Agricultural Organization of the United Nations (FAO) and the Intergovernmental Oceanographic Commission (IOC) of the United Nations Educational, Scientific and Cultural Organization (UNESCO) jointly published the Blue Carbon report, pointing out that more than 55% of global primary production is blue carbon [2]. Moreover, the production efficiency of the coastal blue carbon biomes (mangroves, sea grass, salt marsh ecosystems, etc.) is much higher than that of the Amazon rain forest. However, these blue carbon biomes are being degraded and disappearing at rates 5–10 times faster than rainforests [3], thus protection and restoration are in urgent need. Besides the visible coastal blue carbon, there are enormous invisible blue carbon biomes composed of tiny but extremely abundant microbes, including phytoplankton, bacteria, archaea and viruses, which contribute up to 95% of the world’s blue carbon [4–6]. These microbes can interact with the visible blue carbon biomes, transforming their organic carbon into refractory forms, prolonging the residence time of the organic carbon in the ocean. The environmental issues we are facing in the coastal water today (such as eutrophication, hypoxia, acidification, etc.) also interact with the invisible blue carbon processes, but the mechanisms are not yet clear. Therefore, both visible and invisible blue carbon biomes should be taken into consideration for marine ecosystem services, and understanding their interactions and their relationship with environmental issues is critical for marine ecosystem management and sustainable development. The IOC, Conservation International (CI) and the International Union for Conservation of Nature (IUCN) jointly launched the Blue Carbon Initiative in 2011, aimed at promoting the management of marine and coastal ecosystems through international cooperation, and maintaining carbon sink function in the mitigation of climate change. ‘Blue Carbon Action’ set up two working groups. One is the scientific group toward the establishment of blue carbon measurement and monitoring protocols, data acquisition and quality control, field survey handbooks as well as blue carbon conservation planning and management guidelines. The other is the policy working group toward integration of the blue carbon project into the United Nations Framework Convention on Climate Change and Convention on Biological Diversity, and the development of a program of financial support and other policies. Since then, ‘Blue Carbon Action’ has been in action in the protection and restoration of mangroves, wetlands, etc. in many regions and countries such as Australia, Dhabi, Indonesia, India, Kenya, Madagascar, Vietnam and the USA. Significant progress has been made in coastal blue carbon research in recent years, such as the description of blue carbon status and carbon sequestration potentials at the global scale [7,8] and regional scale [8]; the assessment of impacts of wetland destruction and the proposal of corresponding policy [7]; the evaluation of the eco-value of blue carbon in sea grasses, salt marshes and mangroves (e.g. in Philip Bay and Western Harbor, Australia, with an estimate of the rooted plants to be 1.03 million tons of carbon and a price of $15.38 million) [9]; proposal of countermeasures for conservation and restoration of blue carbon (e.g. in Scotland, Columbia, Korea and other countries) [10,11]; as well as scenario simulation of blue carbon benefit function and market price [12]. In 2017, the Intergovernmental Panel on Climate Change (IPCC) launched the writing process of the Sixth Assessment Report on Climate Change, with a Special Report on the Ocean and Cryosphere in which blue carbon is included. Although the original concept of blue carbon proposed in 2009 refers to the carbon that is captured by marine ecosystems covering both coastal and open waters [3], practical research and development of blue carbon have predominantly involved macrofauna, such as mangrove, seagrass and salt marsh in the coastal zone. After years of promotion of the coastal blue carbon,