A large amount of CO2 has been emitted into the atmosphere due to human activities.
China should develop ocean negative carbon emission technology to support national carbon neutrality, Jiao Nianzhi, academician of Chinese Academy of Sciences (CAS), lately advocates in a paper published on Bulletin of the Chinese Academy of Sciences.
Jiao points out in his article “Developing Ocean Negative Carbon Emission Technology to Support National Carbon Neutrality,” a large amount of CO2 has been emitted into the atmosphere due to human activities, which leads to climate change and triggers environmental problems. Faced with huge challenges, many countries declared the goal of carbon neutrality, and China made a solemn commitment to achieve carbon neutrality by 2060. The two key approaches to carbon neutrality are reducing CO2 emissions and increasing carbon sinks (absorption of atmospheric CO2). Yet not enough attention has been paid to the latter approach though the ocean is the largest active carbon pool on Earth with great potential for achieving negative emissions. As a large emitter and a developing country, China is trying its best to increase carbon sinks and to explore approaches towards negative emissions. “We have established marine carbon sequestration theory, which has laid a solid foundation for negative emissions and set up the linkage between science and policy,” Jiao said.
He states that in the past, carbon sink relied much on terrestrial afforestation; but due to the aggravating contradiction between the shortage of agricultural land and the demand of growing population for food, global carbon neutrality cannot be achieved by this measure alone. By comparison, the ocean has huge potential for negative emissions, which can be the most win-win and cost-effective way to slow down climate warming at present. With rich water and marine resources, China not only has great potential for carbon sink, but can also apply various negative emissions technologies.
Natural ocean carbon sink alone is not enough to achieve carbon neutrality, so it is necessary to develop ocean negative carbon emission (ONCE) technologies. “The application of these technologies can multiply the ocean carbon sink”, writes Jiao in his paper.
The paper reveals that the ocean carbon sink with the most attention now is coastal blue carbon from mangroves, seaweeds, and salt marshes. However, the amount of blue carbon in China’s coastal zone is limited and cannot meet the need for carbon neutrality. Therefore, other approaches to negative emissions are much needed.
The first is to implement land-sea coordination project for negative carbon emissions. Jiao states that the amount of inorganic fertilizers such as nitrogen and phosphorus in agricultural land should be reasonably reduced in view of the over-fertilization and serious fertilizer loss in China’s agricultural land. “This measure can reduce nutrients leakage into rivers and alleviate the eutrophication in coastal waters. Reducing the respiratory consumption of organic carbon and improving the conversion efficiency of RDOC while keeping a high level of carbon sequestration can maximize the total carbon storage, namely the total amount of biological pump (BP) and microbial carbon pump (MCP),” he writes. “Correspondingly, the evaluation system of offshore carbon storage should be established, which should involve not only the sedimentary and buried organic carbon but also RDOC, a previously missed product of MCP.”
China has marine eutrophication in estuaries and coastal areas resulted from the excess fertilizer leaked into rivers with rainwater and finally into the offshore waters, which leads to red tide and green tide. Yet the water quality is not as poor as it seems. “In fact, this forest river has low nutrient content and sufficient dissolved oxygen,” Jiao states in his paper. “The seemingly harmful color demonstrates that it is rich in organic matter, just like the tea. If the environmental condition remains, the organic matter can be preserved for a long time and form into carbon sink with a concentration of more than 1,000 μmol/L, which is over 10 times that of seawater organic carbon in China. Obviously, land–sea coordination is a low-cost and high-benefit ONCE path to reduce carbon emissions and increase carbon sink,” he continued.
The second approach is to research and develop ONCE technologies in anoxic and acidified sea areas. The paper shows that Chinese scientists put forward the principle and technical scheme of implementing negative emissions under anaerobic conditions, which is expected to improve the environment while increasing carbon sink via comprehensive approaches based on the principles of MCP, BP and carbonate pump. “Promoting the production of authigenic carbonates through adding minerals, increasing alkalinity in the anoxic and acidified environment and burying them with organic carbon can increase the carbon storage volume.” Jiao writes.
The third is to implement comprehensive ONCE project in mariculture areas. Global demand for aquatic products is increasing with the growth of the global population and the further shortage of resources. Many problems still need to be solved urgently, such as the ecological load and environmental pressure resulted from large-scale mariculture, especially the ecological risks of seabed organic matter pollution in mariculture areas, the imbalance between supply and demand of nitrogen and phosphorus nutrients, inorganic carbon, dissolved oxygen, as well as eutrophication, oxygen shortage, and acidification in the sea.
Chinese scientists put forward the artificial upwelling measures based on the concept of internal regulation of ecosystem to relieve the ecological and environmental pressure caused by large-scale mariculture and address the imbalance between the supply and demand of nutrients, inorganic carbon, and dissolved oxygen. “Artificial upwelling driven by clean energy such as solar energy can bring nutrient-rich water from the bottom of the mariculture area to the upper layer to supply the nutrients for photosynthesis of the cultured seaweeds,” explains Jiao. “High-concentration nutrients can be released slowly from the bottom in this process, which can avoid ecological disasters such as red tides caused by sudden disturbance events like storm surges. In addition, when the oxygen-rich water from the surface layer was brought to the deep layer, it can moderate the oxygen shortage at the bottom.”
The fourth is to develop a standard system for ocean carbon sink. There is no globally unified standard for ocean carbon sink measurement. Jiao recommends to integrate disciplines related to ONCE and speed up the research on ocean carbon neutrality accounting mechanism and methodology. “Efforts should be made to establish the corresponding methods, technologies, measurement procedures, operation specifications, and evaluation standards of ocean carbon fingerprint, carbon footprint and carbon label, and establish an intact ocean carbon sink trading system,” Jiao appeals.
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