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Human-nature interactions are complex and have important implications for achieving sustainable development goals and addressing other global challenges. Although numerous studies have explored human-nature (or human-environment) interactions and generated useful insights, they are largely disintegrated. Because conceptual frameworks are the foundation of quantitative and qualitative integration, many have been proposed but focus mainly on human-nature interactions within a specific system. To reflect human-nature interactions between distant coupled systems, the framework of telecoupling (socioeconomic and environmental interactions over distances) has been developed. However, no framework has explicitly integrated human-nature interactions between adjacent coupled systems, let alone within a coupled system as well as between adjacent and distant coupled systems simultaneously. To fill such an important gap, in this paper I present an integrated framework of metacoupling: human-nature interactions within a system (intracoupling), between distant systems (telecoupling), and between adjacent systems (pericoupling). A metacoupled system is a set of two or more coupled systems that interact internally as well as nearby and far away, facilitated by agents affected by various causes with various effects. By differentiating and integrating intracoupling, pericoupling, and telecoupling, the metacoupling framework advances a systems perspective on global sustainability and human well-being. The framework can help uncover hidden systemic connections such as spillovers and feedbacks that may not be apparent when focusing on a particular system. To demonstrate the utility of the metacoupling framework, I illustrate its application to human-nature interactions within a global flagship nature reserve as well as between the reserve and the rest of the world. The illustration suggests that the framework has the potential to help holistically understand and integrate human-nature interactions from local to global scales, over time, and among organizational levels. Finally, I offer suggestions for operationalizing the metacoupling framework and discuss the need for new policy, governance, and management for a sustainable future across the metacoupled world.

Telecoupling refers to socioeconomic and environmental interactions between distant coupled human and natural systems, and has become more extensive and intensive in the globalized era. The integrated framework of telecoupling examines flows of information, energy, matter, people, organisms, and other things such as financial capital and goods and products around the globe. It pinpoints causes and effects arising from engagement of diverse agents in the global sphere. This first special feature on telecoupling includes 16 articles that explore diverse telecouplings including trade, migration, tourism, information exchange, and transnational product certification schemes. Here we synthesize the articles by describing eight overarching lessons learned. These include the impact of physical, social, and institutional distance on telecouplings, key roles of agents and their inter-relationships, and the important function of telecoupling in enhancing information signals over long distances. Several lessons directly apply to global sustainability challenges, such as the importance of recognizing trade-offs between local and global sustainability and the need for multi-level management and governance solutions. We also suggest five areas of future research to help propel this nascent field forward and further cement its applicability to addressing global sustainability challenges.

Despite investments in water infrastructure, China must address complex human-nature interactions to ensure supply and quality. A water crisis has prompted the Chinese government to develop an ambitious water conservancy plan. However, the plan may not achieve water sustainability and may cause unintended environmental and socioeconomic consequences, unless it accounts for complex human-nature interactions ( 1 ). Water shortages, for example, force people to find alternatives, such as treatment facilities, whose land and energy requirements aggravate food and energy production, which need large amounts of water. Other nations face similar challenges and share real water from China along international rivers and/or virtual water through trade. Water problems are particularly challenging in China, which has the largest population, fastest-growing economy, rising water demand, relatively scarce water, dated infrastructure, and inadequate governance. We highlight China's water crisis and plan, and then offer recommendations.

Increasing sand extraction, trade, and consumption pose global sustainability challenges Between 1900 and 2010, the global volume of natural resources used in buildings and transport infrastructure increased 23-fold ( 1 ). Sand and gravel are the largest portion of these primary material inputs (79% or 28.6 gigatons per year in 2010) and are the most extracted group of materials worldwide, exceeding fossil fuels and biomass ( 2 ). In most regions, sand is a common-pool resource, i.e., a resource that is open to all because access can be limited only at high cost. Because of the difficulty in regulating their consumption, common-pool resources are prone to tragedies of the commons as people may selfishly extract them without considering long-term consequences, eventually leading to overexploitation or degradation. Even when sand mining is regulated, it is often subject to rampant illegal extraction and trade ( 3 ). As a result, sand scarcity ( 4 ) is an emerging issue with major sociopolitical, economic, and environmental implications.

China's forest cover has been increasing in the past three decades, which is in sharp contrast to rapid declines in other natural resources. Understanding the mechanisms of forest recovery and their effects is essential for sustaining forests in China and elsewhere. Some studies suggest that imports of forest products have contributed to the increase in forest cover of China and the decline in forest cover of exporting countries. However, it is not clear whether other countries beyond the exporting countries are affected. Using the framework of telecoupling (socioeconomic and environmental interactions over distances), we found that China's forest cover increase is affected by multiple telecoupling processes (e.g. trade of food and forest products) and their interactions with each other and with other factors. The socioeconomic and environmental impacts of telecoupling processes go well beyond China and the exporting countries. As China's demand for forest products and other ecosystem services such as food and water continues to rise, telecouplings will become even more important for sustainable forests, food security, water security, human well-being and environmental sustainability in the future. New and more effective policies are needed to minimise negative and enhance positive impacts of telecouplings on China and other countries around the world.

Here we present one of the world’s oldest examples of large-scale and formalized water management, in the case of the Liangzhu culture of the Yangtze Delta, dated at 5,300–4,300 years cal B.P. The Liangzhu culture represented a peak of early cultural and social development predating the historically recorded Chinese dynasties; hence, this study reveals more about the ancient origins of hydraulic engineering as a core element of social, political, and economic developments. Archaeological surveys and excavations can now portray the impressive extent and structure of dams, levees, ditches, and other landscape-transforming features, supporting the ancient city of Liangzhu, with an estimated size of about 300 ha. The results indicate an enormous collective undertaking, with unprecedented evidence for understanding how the city, economy, and society of Liangzhu functioned and developed at such a large scale. Concurrent with the evidence of technological achievements and economic success, a unique relationship between ritual order and social power is seen in the renowned jade objects in Liangzhu elite burials, thus expanding our view beyond the practicalities of water management and rice farming.

Domestic attempts to advance the Sustainable Development Goals (SDGs) in a country can have synergistic and/or trade-off effects on the advancement of SDGs in other countries. Transboundary SDG interactions can be delivered through various transmission channels (e.g., trade, river flow, ocean currents, and air flow). This study quantified the transboundary interactions through these channels between 768 pairs of SDG indicators. The results showed that although high income countries only comprised 14.18% of the global population, they contributed considerably to total SDG interactions worldwide (60.60%). Transboundary synergistic effects via international trade were 14.94% more pronounced with trade partners outside their immediate geographic vicinity than with neighbouring ones. Conversely, nature-caused flows (including river flow, ocean currents, and air flow) resulted in 39.29% stronger transboundary synergistic effects among neighboring countries compared to non-neighboring ones. To facilitate the achievement of SDGs worldwide, it is essential to enhance collaboration among countries and leverage transboundary synergies. Domestic attempts to advance the Sustainable Development Goals (SDGs) in a country can have synergistic and/or trade-off effects on the advancement of SDGs in other countries. Here the authors demonstrate that while high-income countries make up only 14% of the global population, they drive over 60% of worldwide SDG interactions.

Gross domestic product (GDP) summarizes a vast amount of economic information in a single monetary metric that is widely used by decision makers around the world. However, GDP fails to capture fully the contributions of nature to economic activity and human well-being. To address this critical omission, we develop a measure of gross ecosystem product (GEP) that summarizes the value of ecosystem services in a single monetary metric. We illustrate the measurement of GEP through an application to the Chinese province of Qinghai, showing that the approach is tractable using available data. Known as the “water tower of Asia,” Qinghai is the source of the Mekong, Yangtze, and Yellow Rivers, and indeed, we find that water-related ecosystem services make up nearly two-thirds of the value of GEP for Qinghai. Importantly most of these benefits accrue downstream. In Qinghai, GEP was greater than GDP in 2000 and three-fourths as large as GDP in 2015 as its market economy grew. Large-scale investment in restoration resulted in improvements in the flows of ecosystem services measured in GEP (127.5%) over this period. Going forward, China is using GEP in decision making in multiple ways, as part of a transformation to inclusive, green growth. This includes investing in conservation of ecosystem assets to secure provision of ecosystem services through transregional compensation payments.

Cities are the engines for implementing the Sustainable Development Goals (SDGs), which provide a blueprint for achieving global sustainability. However, knowledge gaps exist in quantitatively assessing progress towards SDGs for different-sized cities. There is a shortage of relevant statistical data for many cities, especially small cities, in developing/underdeveloped countries. Here we devise and test a systematic method for assessing SDG progress using open-source big data for 254 Chinese cities and compare the results with those obtained using statistical data. We find that big data is a promising alternative for tracking the overall SDG progress of cities, including those lacking relevant statistical data (83 Chinese cities). Our analysis reveals decreasing SDG Index scores (representing the overall SDG performance) with the decrease in the size of Chinese cities, suggesting the need to improve SDG progress in small and medium cities to achieve more balanced sustainability at the (sub)national level.

Food waste has a great potential for resource recovery due to its huge yield and high organic content. Oriented fermentation is a promising method with strong application prospects due to high efficiency, strong robustness, and high-value products. Different fermentation types lead to different products, which can be shifted by adjusting fermentation conditions such as inoculum, pH, oxidation-reduction potential (ORP), organic loading rate (OLR), and nutrients. Compared with other types, lactic acid fermentation has the lowest reliance on artificial intervention. Lactic acid and volatile fatty acids are the common products, and high yield and high purity are the main targets of food waste fermentation. In addition to operational parameters, reactors and processes should be paid more attention to for industrial application. Currently, continuously stirred tank reactors and one-stage processes are used principally for scale-up continuous fermentation of food waste. Electro-fermentation and iron-based or carbon-based additives can improve food waste fermentation, but their mechanisms and application need further investigation. After fermentation, the recovery of target products is a key problem due to the lack of green and economic methods. Precipitation, distillation, extraction, adsorption, and membrane separation can be considered, but the recovery step is still the most expensive in the entire treatment chain. It is expected to develop more efficient fermentation processes and recovery strategies based on food waste composition and market demand.