Analysis of Agricultural Carbon Emissions and Carbon Sinks in the Yellow River Basin Based on LMDI and Tapio Decoupling Models

Greenhouse gas (GHG) emissions are considered to be the root cause of environmental problems such as global warming [1], sea level rise, and frequent severe weather [2,3]. It is predicted that global CO₂ emissions may increase the Earth’s temperature by 1.5 to 2 °C in the future [4], posing a serious threat to the survival and development of human beings [5]. The Paris Agreement, the first historic global climate change agreement, was signed by 178 countries around the world in 2016 [6], aiming to slow down climate warming and increase the capacity to tackle climate change by limiting global warming to 1.5 degrees Celsius. However, this topic is particularly important for the BRICS countries because of their speedy economic growth and contribution to worldwide economic expansion [7,8]. The BRICS countries rank high in energy usage in comparison to other emerging countries because of their large populations and promising economies. Due to this great economic expansion, the BRICS account for around 41% of Earth’s energy usage and are key contributors to CO₂ emissions. Because of the higher economic expansion of the BRICS, the total CO₂ emission per capita is 13.98 trillion tons, contributing to 41.7% of Earth’s CO₂ emissions [9]. Moreover, China, India, Russia, and Brazil are among the top seven countries with the largest CO₂ emissions, the leading cause of environmental damage [10]. Agriculture accounts for the largest shares of global anthropogenic carbon dioxide (CH₄) and nitrogen dioxide (N₂O) emissions among all sources of GHG emissions, about 52% and 84%, respectively [11]. GHG emissions from agriculture and food production have increased by 17% globally over the past three decades and agrifood systems accounted for up to 31% of global anthropogenic emissions of carbon dioxide (CO₂) in 2019 [12].

China, as the most populous country in the BRICS nations and the world, faces the challenge of relatively underdeveloped agriculture due to its large population. China is one of the premier agricultural countries in the world, with an increase in crop production of 46.3% from 2000 to 2015, accounting for 19.9% of the global production [13]. China’s CO₂ emissions reached 11.50 billion tons in 2014, accounting for 35.6% of the world total [14]. Moreover, China’s traditional agricultural production produces 17% of the world’s greenhouse gases [14]. Agricultural carbon emissions are usually mainly divided into crop production and livestock farming [15]. Fertilizers, with the highest CO₂ emissions from agricultural land, are considered to be an important measure to alleviate the pressure on China’s agriculture in the context of limited resources, scarce arable land, and rapid population growth [16]. China consumes 40% of the world’s fertilizers and has become the largest fertilizer user [17,18], and the increase in CO₂ emissions from agricultural production is a direct result of the overuse of fertilizers. China has ranked first in the world in the production of major livestock products since 1985, and its average annual CH₄ emissions from animal husbandry grew by 2.2% annually from 2004 to 2013 [19]. China’s traditional agricultural production produces 17% of the country’s greenhouse gases [14]. In China, rice, corn, and wheat account for over half of the total grain production. Since 2000, China’s grain output per unit of area has increased by 26.38%, while the use of chemical fertilizers, pesticides, and agricultural film has increased by 45.25%, 41.23%, and 93.21%, respectively [5]. Frequent changes in land use, excessive resource use, and improper waste disposal also contribute to carbon emissions [20]. It is worth noting that these previous studies argue that China’s phosphorus footprint accounts for a large global proportion. Around 42% of the total phosphorus exceedance footprint in the world was argued to come from China [21], and it is expected to keep increasing in the future. According to a report released from a Chinese phosphorus company about the GHG emissions during phosphorus processing in 2019, the total GHG emissions were estimated to be about 0.777 million tons of CO₂-equivalent during phosphorus fertilizer production from the phosphoric acid and ancillary production units [22]. In 2015, China’s production of phosphorus fertilizer was nearly twice that of developed countries [23]. The substantial greenhouse gas emissions associated solely with phosphorus fertilizer production prompt contemplation of the potential impact of agricultural fertilization on greenhouse gas emissions, the magnitude of which is immeasurable. Currently, greenhouse gas emissions from agricultural activities account for 16–17% of China’s total emissions, significantly higher than the global average of 13.5% [24]. To address the climate change risk, more than 100 countries worldwide pledged to become carbon-neutral by the end of 2020. China also proposed a “dual carbon” development target of a “carbon peak” and being “carbon-neutral” in 2020. Agriculture is a major contributor to global carbon emissions, and as a traditional agricultural country, carbon emissions reduction in China’s agricultural sector cannot be ignored [25].

The Yellow River, known as the mother river of the Chinese nation, is the cradle of Chinese civilization. The Yellow River basin (YRB) spans the three major economic zones in eastern, central, and western China, mainly involving agriculture and animal husbandry, playing a pivotal role in the national economic development. Serving as an essential ecological barrier and a typical region affected by global warming, its ecological protection and high-quality development have been elevated to a major national strategy [26]. The YRB is an important ecological barrier and economic development belt in China; however, the economic and social development mode, focused on agricultural production and energy development, does not match the environment carrying capacity of the YRB. In 2021, the China Central Committee of the Communist Party of China and the State Council issued an outline document on the ecological protection and high-quality development of the Yellow River basin, pointing out that efforts should be made to strengthen ecological protection and management, ensure the long-term stability of the Yellow River, promote high-quality development, and improve the lives of the people [27]. The YRB is one of the principal traditional farming areas in China, where intensive agricultural production methods have caused problems such as water resource reduction and environmental pollution, which have led to a bottleneck in the low-carbon development of agriculture. Moreover, a serious challenge was given to the national agricultural plan due to the long period of crude inputs of agricultural materials and the irrational structure of the agricultural industry in the early period [28]. Despite being only 15% arable land [29], the YRB has a grain output of 232.69 million tons, accounting for 35.37% of the national grain total. The unit area ratio of the grain production is far greater than the arable land, thus the GHG emissions from agriculture in the YRB should not be ignored.

There are two primary ways to reduce the concentrations of greenhouse gases in the atmosphere, through energy conservation and promoting the use of renewable energy sources, and the other way is to increase carbon sinks [30]. However, agricultural carbon emission sources differ from other emission sources. In addition to being an important source of carbon emissions, crops themselves have the function of being carbon sinks, fixing carbon in the soil, which is of great significance for carbon emission reduction. However, previous studies calculating [31,32,33] carbon emissions have tended to ignore the importance of carbon sequestration in the process of crop production, resulting in a large deviation between the results of the accounting and the actual situation, and giving policy recommendations that cannot address the root causes of carbon emissions. The accurate assessment of carbon emissions is an important prerequisite for formulating effective carbon reduction policies and ensuring their implementation, thus adding carbon sinks into the carbon emission system is of great significance.

Given the importance of reducing agricultural carbon emissions in mitigating climate change, strategies for mitigating agricultural carbon emissions have become a hot research topic among scholars. Accurate quantification of agricultural carbon emissions and carbon sequestration can facilitate the achievement of sustainable agriculture and climate change mitigation [34]. In order to reduce agricultural carbon emissions, it is essential to identify their sources. Some scholars argue that the major sources of agricultural carbon emissions come from inputs such as fertilizers, pesticides, and agricultural machinery [35]. On the other hand, Deng argues that agricultural soil use is the main driver of agricultural carbon emissions, accounting for about 70% or more of total carbon emissions from agricultural sources [36]. While other scholars have argued that carbon emissions from agriculture come mainly from livestock enteric fermentation, manure management, rice growth, and the arbitrary disposal of agricultural waste [37].

Research in the academic community on agricultural net carbon sinks primarily focuses on several aspects: Firstly, the calculation of agricultural net carbon sink amounts and the analysis of their distribution patterns in different times and spaces [38]. Secondly, attention is given to the study of agricultural carbon sink trading and compensation mechanisms [39], involving ecological compensation issues, compensation principles, compensation methods and standards, as well as the monitoring of forest carbon sink trading [40]. Additionally, research has been conducted on related systems, policies, and comparisons of carbon trading among different countries [41]. Overall, scholars have conducted extensive research on agricultural carbon sequestration measurement, factors influencing sequestration, carbon sequestration trading and compensation mechanisms, and the prospects for carbon sequestration development. Comparing this study to the research findings of other scholars, the existing studies mainly focus on forest carbon sequestration, with limited research on the role of cereal crops as a carbon sink. The author’s research approach aims to investigate the carbon sequestration capacity of the same crop in different regions and whether there are regional differences in the carbon sequestration capacity of these crops. If regional differences exist, strategically planting crops with higher carbon sequestration capacity can contribute to the reduction of carbon emissions.