1. Introduction
Global warming is one of the most important environmental problems facing humanity in the 21st century. Many countries around the world are working to resolve it through climate negotiations and the formulation of domestic environmental laws. The major achievement of the climate negotiations, the Paris Agreement, which establishes a model of cooperation between the nations of the alliance, came into effect at the end of 2016. Most of the countries and regions have focused their efforts on the control and reduction of greenhouse gas emissions, and some countries have been advanced in forest carbon sinks, while they paid little attention to the most efficient approach to help fix and store carbon—blue carbon.
Blue carbon refers to the processes, activities and mechanisms that utilize marine activities and organisms to absorb and store carbon dioxide in the atmosphere. Previous studies have shown that the most efficient blue carbon ecosystems are seagrass beds, mangroves, and salt marshes [
1]; other results report that large seaweeds, shellfish and micro-organisms [
2] also show outstanding performance in the fixation and storage of carbon. The carbon sequestration capacity of coastal blue carbon is far greater than that of the terrestrial carbon pool in per unit area [
3]. However, due to the narrow pursuit of economic value, about one-third of mangroves, seagrasses and salt marshes have begun to degenerate or disappear due to reclamation, deforestation, coastal aquaculture, coastal land development, industrial production and climate change [
4,
5,
6,
7]. Thus, strengthening blue carbon protection on a global scale has become a vital and urgent initiative.
Promoting blue carbon protection mainly depends on cooperative development and common protection of the ocean. In recent years, China has been at the forefront of the world in blue carbon research. The theoretical framework of the marine microbial carbon pump (MCP) proposed by the team of Academician Jiao Nianzhi explains the source of the ocean’s huge dissolved organic carbon pool (new blue carbon), which has received extensive attention and recognition from international counterparts [
8], and has been featured on many covers of top publications such as
Nature and
Science. Using major MCP processes, a coupled physical-ecosystem model in the South China Sea (SCS) has been developed and the results suggest that the role of the MCP might become more significant under future climate change conditions [
9]. The cost-and-benefit pricing model of the blue carbon sink in marine ranching has been constructed to help China build a perfect blue carbon sink exchange trading market [
10]. Meanwhile, many countries and regions, including Partnerships in Environmental Management for the Seas of East Asia (PEMSEA) countries, recognize the importance of mangroves and try to build awareness and accelerate practical action on blue carbon by improving quantification of greenhouse emissions, measuring the significance of coastal blue carbon ecosystems across different policy frameworks and developing climate change vulnerability assessments, adaptation and resilience plans.
The Maritime Silk Road (MSR) can be an important bridge for economic and cultural exchanges between the East and the West, and the cooperation between countries is closely linked through trade along the road. The economic development of the MSR follows a trend of high at both ends and low in the middle: the economic development of East Asia and Europe enjoys strong momentum, while the economic growth of central Asia and the Middle East is relatively slow. Although the industrial division and cooperation along the MSR is immature, the ongoing development is highly complementary [
11]. In view of the economic development pattern, by taking advantage of China’s leading edge in blue carbon research, the blue carbon cooperation along the Silk Road can optimize the new pattern of Eurasian development space, so as to promote the sustainable economic development of the MSR.
One of the cooperation actions is that, in a recent report, around fifty countries—including the majority of East Asian countries—have started building deforestation and forest degradation implementation frameworks, with financial support from developed countries. These frameworks have habitat (mangroves) overlap with blue carbon interventions. Many countries, especially China, Malaysia and partially Vietnam, have formulated reduction targets related to the amount of CO
2 emitted per unit of GDP, which included in the country’s so-called nationally determined contribution. This report considered the economic and environmental issues associated with blue carbon in East Asia and is the most detailed blue carbon report so far. In addition, this report introduced the current blue carbon measurements and protection measures in East Asian countries, and proposed some practical steps to promote blue carbon intervention, including awareness building, knowledge sharing and exchange of best practices. These measures provide direction for domestic and international blue carbon protection, but the report did not emphasize the importance of international cooperation, let alone the specific implementation of international blue carbon cooperation [
12].
Based on the initiative of the “Blue Carbon Cooperation Program along the 21st Century Maritime Silk Road” proposed by the Chinese government, Zhang et al. [
13] summarized the driving force, realization and guarantee mechanism of the international blue carbon cooperation by reviewing China’s blue carbon resources and maritime international cooperation on the MSR. The author believed that the development of blue carbon needs to form a consensus at various levels at home and abroad to seek common cooperation. By establishing the realization and guarantee mechanism of blue carbon cooperation, a path of blue carbon development can be opened under the framework of a cooperation mechanism to achieve the goal of joint development. Besides, the importance of technological and financial support has been mentioned many times in this article, which is in line with the knowledge sharing and blue economy mentioned in the East Asian Blue Carbon Report. Still, this article did not give a specific implementation plan.
This lack of an explicit consideration of the influencing factors and specific implementation on achieving blue carbon cooperation lead to the following research questions:
The answers to these questions provide a reference for blue carbon international cooperation and provide solutions for countries along the MSR to jointly address global climate change and environment issues.
In this research we propose a complex network with non-trivial topological features. Based on the complex network theory, a map of blue carbon corporation networks along the MSR is constructed, which can push development of sustainable marine environment by integrating coastal resources along the MSR. After that, this paper combines the decision-making structure type to establish and simulate a game model on the basis of network, and analyzes the influence of different factors on promoting the blue carbon cooperation among countries along the MSR, which aims to provide references and guidelines for the blue carbon cooperation countries along the road, accelerate the development of regional trade, and most importantly, promote the sustainable development of marine environment on the MSR to mitigate global warming problems. In contrast to former studies, our research established a game model of blue carbon cooperation and used simulation analysis to simulate this cooperation and observe the impact of the influencing factors.
The next part of the article provides a literature review on blue carbon. The third part constructs a complex network of blue carbon cooperation on the MSR and establishes a network game model based on the interpretation of the decision-making structure model and realistic conditions. In the fourth part, the simulation method is used to simulate the network game model of the MSR. The final section summarizes the conclusions of the simulation graphics and explores measures to promote blue carbon cooperation on the MSR in order to answer the research questions.
2. Literature Review
Blue carbon protection is scientifically credible. In the past 10 years, research on “blue carbon” has increased significantly due to the global environmental threats the world is facing. From the literature review, it is clear that scholars have focused on the scientific mechanism, technical development and application, and involved with the sustainable development of blue carbon. The principal economic, regulatory and political issues of blue carbon that emerge are discussed [
14,
15].
The most representative global achievement in blue carbon research is “Blue carbon: A UNEP rapid response assessment”, a report jointly issued in 2009 by the United Nations Environment Programme (UNEP), Food and Agriculture Organization (FAO) of the United Nations, United Nations Educational, Scientific and Cultural Organization (UNESCO), and the Intergovernmental Oceanographic Commission [
16]. The report elaborates on six aspects of carbon fixation, ocean and climate, functions and present situation of blue carbon, significance to human society, and ways of change.
In the scientific mechanism and technical research of blue carbon, Garrard [
17] studied the effects of ocean acidification on carbon storage and integration in seaweed beds. Murdiyarso [
18] believed that Indonesia has lost 40% of mangroves for aquaculture development over the past 30 years, resulting in annual emissions of 0.07 to 0.21 PgCO
2e (Pg is the unit of carbon storage, 1 Pg = 10
15 g). Duarte [
19,
20,
21] studied the main functions of marine vegetation in the marine carbon cycle and assessed the carbon storage in marine vegetation sediments. Pendleton [
22] estimated the amount of carbon dioxide released into the atmosphere when the blue carbon ecosystem degrades, and found that it yielded CO
2 emissions of between 0.15 and 1.02 million tons per year. Sanders [
23] postulated that if mangrove deforestation is curbed, global mangrove carbon stocks may increase by nearly 10% by 2115 due to increased tropical rainfall. Meanwhile, Li et al. [
24] evaluated the dynamics of blue carbon storage in coastal wetlands under coastal reclamation in China, and found that more than 380,000 hectares of coastal wetlands were affected by reclamation between 1990 and 2015, which led to a release of ca. 20.7 Tg (ca. means circa/about, 1 Tg = 10
12 g) of blue carbon, accounting for 72.5% of total carbon loss.
In the management and cooperation research of blue carbon, Lovelock [
25] proposed a framework for assessing the risk of carbon dioxide emissions caused by degraded soil, and from his findings constructed carbon value form. Laffoley [
26] published book on coastal carbon sink management, and Vierros [
27] pointed that the management and protection of blue carbon ecosystems could encourage collaboration between climate change and biodiversity practitioners on the national and international levels.
All the research results have proved that (i) the scientificity and feasibility of blue carbon protection, (ii) the necessity of strengthening the international cooperation of blue carbon protection, and (iii) the specified design path of the incentive and punishment mechanism of carbon sink, which provide a theoretical basis for exploring and analyzing the quantitative model of blue carbon international cooperation. However, the existing research has not focused on the design of the blue carbon cooperation model of the MSR, which is the major international transportation hub. The resulting construction of ports, the balanced development of the port network and the regional cooperation along the MSR can help to optimize routes, reduce energy consumption, promote regional trade, and achieve sustainable development goals [
28].
Since 1980, 20% of the world’s mangroves have been destroyed, which greatly accelerates the deterioration of the climate. If the blue carbon with a combined area of only 2% to 6% of the tropical forest area is destroyed, the carbon emissions will be about 19% higher than the effects of deforestation [
29,
30,
31,
32]. According to a blue carbon report published by PEMSEA, East Asian countries, which the blue carbon ecosystems are heavily concentrated in, have the world’s largest coastal carbon stocks and some of the most vulnerable coastal communities to the influences of climate change. All three blue carbon ecosystems—mangroves, tidal marshes and seagrass meadows—occur in East Asia. Tidal marshes occur primarily in China, Japan, North Korea and South Korea. It is speculated that less than 60,000 ha of tidal marsh remains across the region. Seagrasses are extensive but hard to assess accurately due to their subtidal location. Although there is a lack of data on seagrass distributions, several surveys are conducted to specific countries. For example, estimates of 3,000,000 ha of seagrass beds occur throughout Indonesia and all the Indonesian seagrasses contain 368.5 million metric tons of CO
2 within the plants and soil. Mangroves are the dominant ecosystem type covering most of East Asia. Current status of mangrove ecosystem’s distribution in East Asia, estimated carbon stocks and estimated emissions due to ecosystem loss are shown in
Table 1. Among them, MFW and Biome (TEOW) refer to the Mangrove Forests of the World dataset and the Terrestrial Ecosystems of the World dataset respectively, which were mapped to assess the status of mangrove [
12,
33].
Countries have been gradually raising the awareness of blue carbon. China, Vietnam, Thailand, the Philippines and Japan have been strong performers in early carbon emissions trading. The Philippines explicitly mentions the potential of blue carbon, and Vietnam highlights the need to protect, restore and improve coastal forests. Japan and Korea show their interest in forest carbon emissions projects [
12]. While actions each country take within national borders to support coastal blue carbon ecosystems are efficient, the problem of climate change is a global issue that requires the active cooperation and joint efforts among all the countries.
It can be seen from the above literature that the current researches on blue carbon-related papers are mainly based on the measurement of blue carbon, and many papers have deduced the measures or paths for the development of blue carbon cooperation; blue carbon reports published by some organizations mainly use statistical methods to specifically explain and analyze the distribution of blue carbon ecosystems, the status of carbon sequestration and carbon storage, and international cooperation, additionally, have pointed out the future trends. Among them, blue carbon reports provide more information on blue carbon-related cooperation projects between different countries or regions. The blue carbon accounting rules, issued by the Intergovernmental Panel on Climate Change, recently was updated with a dedicated section to set a unified accounting standard for national reports on blue carbon emissions from mangroves, tidal marshes and seagrass meadows, which is conducive to the formation of blue carbon cooperation among countries. Besides, blue national appropriate mitigation actions (NAMAs), which were first introduced under the Bali Action Plan for developing countries to develop specific mitigation actions, are under preparation or implementation worldwide, including the NAMA for the sustainable development of Peatland in Indonesia [
12]. All of these provide a cooperation basis for blue carbon. On the other hand, blue carbon cooperation is a joint effort of marine protection whereby all countries on the MSR can gain spillover effects and social benefits from the activities. Many pilot projects are ongoing all around the world, and their smooth progress can provide valuable experiences and references [
14].
Although carbon stock, emissions and removals data for blue carbon ecosystems remains incomplete, and guidelines for monitoring, accounting, etc. are not readily available, blue carbon collaboration can be advanced by using coastal ecosystems protection as climate finance projects in the East Asia blue economy and constructing carbon crediting mechanisms. Regional and global organizations and initiatives, such as PEMSEA, the Blue Carbon Initiative, the Partnership for Blue Carbon and others, can also help to facilitate further cooperation. The blue carbon report published by PEMSEA suggest that PEMSEA countries can take a framework of actions to advance the management of blue carbon ecosystems, climate response planning, blue economy growth and facilitate regional and cross-border blue carbon collaboration, which includes three aspects of awareness building, knowledge exchange and acceleration of practical actions. During the building of awareness, countries can include blue carbon into their policy dialogue, applying the 2013 Intergovernmental Panel on Climate Change (IPCC) wetland supplement in their nation and report trends of coastal ecosystems’ status, threats and change through time. By contributing to technical and policy workshops, supporting science programs and technical analysis and developing knowledge products and demonstration activities, PEMSEA countries can facilitate relevant knowledge exchange. As to acceleration of practical action, including blue carbon ecosystems in national economic development plans, correlating health of blue carbon ecosystems with industry inputs and outputs of blue economy and including management of blue carbon ecosystems within coastal management plans can be efficient [
12]. Thus, it is realistic to promote blue carbon cooperation along the MSR.
In June 2017, the Chinese government issued the “One Belt and One Road Maritime Cooperation Vision”, clearly proposing the idea of “strengthening cooperation on oceans to cope with climate change” and “strengthening international cooperation in blue carbon”. Currently, the Chinese government is actively leading the countries along the MSR with the focus on blue carbon cooperation to jointly address climate change and manage the international environment. Based on this, Wang [
34] analyzed the significance of the development of blue carbon in Guangdong Province of China to control greenhouse gas emissions, protect the marine ecological environment and implement the “Belt and Road” construction, and gave the main paths and measures as solutions for the development of blue carbon in Guangdong Province. Zhang [
13] analyzed the national blue carbon cooperation mechanism along the MSR, including three aspects: the driving force mechanism mainly based on the common aspiration of governments to jointly manage the global climate environment; the realization mechanism includes cooperation and protection of marine biodiversity and marine environments, cooperation monitoring of blue carbon ecosystem and cooperative management of marine pollution; guarantee mechanism includes blue carbon cooperation research, high-level ocean dialogue, blue carbon cooperative financing, blue carbon market construction, blue carbon financial support and blue carbon industry support. It can be seen that some scholars have paid attention to the relationship between the MSR and blue carbon, and provide a technical basis and scientific basis for the efficiency improvement of blue carbon cooperation, and offer technical support for the blue carbon cooperation of the MSR. However, as mentioned earlier, the social nature of blue carbon cooperation and the guarantee mechanism for sustainable development are still at an early stage of exploration, and the specific implementation of the blue carbon international cooperation has not been proposed. It is necessary to provide scientific solutions and explore the impact of the influencing factors.
Analogous to the approach of Arctic environmental governance, Fan et al. [
35] studied the cooperative behavior of arctic governance among countries in a complex network based on the evolutionary game model, and drew the conclusion that some factors have an impact on the behavior choice of countries, and provided a reference for China’s participation in arctic environmental governance and decision-making. By introducing the incentive mechanism of human social organizations, Xie [
36] found that the incentive mechanism generally promotes the evolution of cooperative behavior in different network structures. Since that the participants in blue carbon cooperation have behaviors of learning and imitating [
37], it is feasible to use a game model. This kind of behavior can be explained by the strategy update and network topology involved in the evolutionary game research. However, the general evolutionary game model is always based on the assumption of rational economic man [
38], which is unrealistic. Considering the differences in various aspects of decision-making participants, it is more realistic and convincing to introduce the structural model of decision-making rules into the game model to simulate the strategic choices of various countries in blue carbon cooperation, and provide reference for the blue carbon cooperation and alleviate carbon emissions as possible.
5. Discussion and Conclusions
In this research, we constructed a blue carbon collaboration network along the MSR. By applying a simulation approach, we explored the influence of different factors on the final number of cooperators which include: different types of decision makers, initial input cost, annual fixed input cost, discount rate of income, cost-return coefficient, subsidy rates given by neighboring countries, carbon tax, and the reduction rate of carbon-containing commodities. The theoretical analysis and simulation results of the simulation model can be concluded as follows:
5.1. Conclusion
First, the decision-making type of the MSR countries has a certain impact on the blue carbon cooperation of the network. The more decision makers of the equal-choice strategy there are, the easier it is to achieve the blue carbon cooperation of the network; and the greater the number of rational and savvy decision makers, the more unstable the state of achieving all cooperation is and the more likely it is to fluctuate. Our research divided the decision makers into five types that presented various results. When considering the realistic factors, however, the decision-making behavior between countries could be even more complex, which makes it difficult to analyze the actual blue carbon cooperation between countries along the MSR.
Second, when considering the cost, whether it is the initial input cost or the fixed input cost, the larger the investment, the greater the gain in a certain range. However, it is worth noting that the benefits appear to be more sensitive to annual fixed input costs, which may be related to subsequent blue carbon management and maintenance efficiency. For the promotion of the blue carbon cooperation, the current technologies related to blue carbon are not mature enough, and excessive investment at the beginning may lead to a waste of capital. Each node country can determine a reasonable initial input value for blue carbon planting, and then invest in the maintenance of the blue carbon ecosystem during its growth period.
Third, investment return coefficient and neighbor subsidy rate have positive effects on blue carbon cooperation along the MSR. In fact, the investment return coefficient is associated with the blue carbon output efficiency of an ecosystem; that is, the higher the output efficiency, the more likely that the relevant countries obtain higher returns, which will further promote the investment in the industrial chain formed by these countries. The spillover effects of blue carbon ecosystem will promote neighbor countries’ blue carbon production, and showcase a positive demonstration effect of the cooperation.
Fourth, the results mentioned above that a high carbon tax rate would be detrimental to cooperation have caused us to ponder. Blue carbon production is a sustainable development model which includes three aspects of economic, social and environmental aspects. A carbon tax would inhibit manufacturing exports, while some MSR countries are in the pre-economy and take-off phase and, currently, the constructions taking place in these countries are generating significant blue carbon damage due to the explosion of shipping and the construction of deep-sea ports (Chittagong, Gwadar, etc.). The carbon tax is not conducive to these countries’ development of manufacturing, restraining exports, and reducing economic performance. Therefore, some countries will be resistant to the carbon tax system.
Finally, from the results of comprehensive comparative simulation, it can be concluded that the effect of the reward mechanism is better than that of the penalty mechanism. This conclusion is consistent with people’s aversion to risk and has pointed out the direction for the design and promotion of the blue carbon cooperation mechanism. In the process of blue carbon cooperation on the MSR, more incentives for investment mechanism design are needed to form a positive expectation of cooperation and to promote cooperation. Of course, in order to curb the “free rider” problem, an appropriate punishment mechanism is also necessary. The carbon tax mechanism should be developed in MSR countries and, when there is a large export deficit of carbon-containing commodities, it will effectively curb the carbon emission behavior of these countries and reduce environmental pollution.
5.2. Contributions and Limitations
Our research is among one of the first to apply the quantitative model to study the blue carbon cooperation mechanism of the MSR. The conclusions of the research provide a theoretical basis for the policy regulation and management decision-making of the blue carbon cooperation of the MSR. According to our findings, China’s blue carbon cooperation to promote the economic network of the MSR can start from the following aspects: First, increase the investment of blue carbon scientific research funds, to support academic research and develop new technologies to improve the efficiency of blue carbon output, and share and cooperate with the coastal countries on the MSR. This is consistent with the knowledge sharing mentioned in the previous literature, like in the PEMSEA report [
12], and our results highlight the benefits of sharing blue carbon production technologies.
Second, the establishment of a blue carbon investment finance organization can be advocated, through which the financing of blue carbon can be carried out to provide financial support and guarantee for the blue carbon investment of countries along the MSR. The national governments along the MSR can guide through policies to increase the credit inclination of financial credit for the development of the blue carbon industry. Financial institutions can increase financial support for blue carbon industry research and development (RD) companies based on environmental quality assessment elements and green credit assessment systems, and form strong blue carbon financial support. For example, financial support can be provided for investing in blue carbon ecosystems or blue carbon protection. Such financial support will bring economic benefits, and with the support of the technology, there will be a considerable return, thus promoting the development of the blue carbon economy.
In addition, we propose the establishment of a blue carbon trading market, using the market mechanism to subsidize those countries engaged in blue carbon production, and improve the initiative of blue carbon production of MSR countries. However, the establishment of the blue carbon trading market must first establish a systematic market trading system with clear trading subject rules, trading method rules and pricing rules, and then the trading market can be improved gradually. This also requires a long exploration period.
We also suggest the establishment of the carbon tax alliance along the MSR for countries to reach an agreement on carbon tax through negotiation, and use the carbon tax mechanism to curb carbon emissions and promote energy conservation and emission reduction. Of course, this action needs to take the particularities of developing countries along MSR into account.
Our innovative contributions of the research are as follows: first, the decision structure model is introduced into the research of the blue carbon cooperation mechanism, and the game model is used to study the specific implementation of the blue carbon cooperation along the MSR, which is like reaching a common governance agreement or forming a governance alliance in the MSR counties. To some extent, this answers the Q1; “how to achieve the blue carbon international cooperation?”. Considering the impact of decision types on blue carbon cooperation provides a reference for establishing a more realistic cooperation model; the discounted present value of future income and other factors are also introduced into the blue carbon investment returns to make the simulation conclusion more consistent with the actual decision-making process. At the same time, the results obtained by simulating the game model using Matlab software answers the question “What is the impact of factors in the implementation process on blue carbon cooperation?”.
In addition, the topic of blue carbon cooperation was combined with the MSR for cross-research, which expand the scope of cooperation and provide a new adhesive for the community construction of the MSR.
Nevertheless, this research has the following limitations: the assumptions of the model are still idealistic, the requirements are too strict, and there is a gap between the randomness and irrationality of the cooperation strategy selection of realistic countries. National decision-making is not always rational. It is influenced by many factors such as geopolitical factors, international economic structure, and national security. Under certain conditions, geopolitical and national security factors take precedence over economic development. MSR countries may choose blue carbon non-cooperation strategies due to political factors. In the future research, the latest behavioral economic theory can be introduced into the model construction to increase the geopolitical and national security factors and relax the variable constraints. This would make the model more realistic and the corresponding governance of carbon emissions more feasible.