Key Issues of Earth System Science in the Study of Carbon Sinks in the Loess Plateau

With the global temperature rising by 1.2 ℃, it is urgent to deal with climate change. In September 2019, the Chinese government promised that China will reach its carbon peak in 2030 and become carbon neutral in 2060, which is a huge responsibility and a huge challenge. The achievement of carbon neutrality requires energy conservation and emission reduction, as well as negative emission technologies and an increase in ecological and geological carbon sinks. The adjustment of the energy structure and the development of negative emission technologies such as CCUS will take decades. There is an urgent need to investigate and study the current status of ecological and geological carbon sinks and increase the potential of carbon sinks. The global carbon sink inventory mainly relies on the "top–down" and "bottom–up" estimation methods, while the national–level regional carbon sink inventory is still a difficult problem. The Loess Plateau is the first area where the ecological project of returning farmland to forests and grasslands started, and it is also an ecologically fragile area. The current investigation and research on carbon sinks in the Loess Plateau is still in its infancy. Based on the needs of the national carbon neutral strategy and the construction of ecological civilization on the Loess Plateau, this paper begins to review the research results of carbon sinks on the Loess Plateau from the perspective of earth system science. Firstly, the method system of carbon sink assessment in the Loess Plateau is summarized, and then it is further summarized that the carbon sink system of the Loess Plateau mainly includes organic carbon sink system and inorganic carbon sink system. Among them, the organic carbon sink system includes the research on the organic carbon storage sub-system and the ecological carbon sink system. The inorganic carbon sink system mainly includes carbonate carbon sink system and silicate carbon sink system. Finally, from the perspective of earth system science, the suggestions are given for the investigation and research of carbon sinks in the Loess Plateau.