**5. Conclusions**

New Caledonia is currently facing important interconnected economic, resources, and environmental issues.

As Wiedman et al. mention: "Two fifths of all global raw materials were extracted and used just to enable exports of goods and services to other countries" [67]. As an extractive economy, it provides important nickel resources to the world. But far from ensuring flourishing economic perspectives through a positive trade balance, the situation increases its material dependency by requiring imports of huge amounts of energy resources in order to enable nickel production. Two thirds of local energy consumption, based mainly on imported fossil fuels, and half of CO2 equivalent emissions are caused by the nickel production industry.

As an island, and although responsibilities can be attributed to nickel consuming countries, New Caledonia indirectly contributes to weakening its own position against the rise of sea level provoked by climate change, through its local emissions of greenhouse gases. The situation of the island also emphasizes the issue of land availability and local pollution considering the huge amounts of waste generated by nickel extraction and production. Indeed, we cannot neglect the wider environmental impacts of nickel mining in New Caledonia, which is in addition to being a very high greenhouse gas emitting industry, resulting in very significant land-use changes (from mines but also sedimentation of slags), acidification, and eco-toxicity, according to life cycle assessments studies [75,76]. A future in which the nickel reserves could be exhausted is not currently envisaged in New Caledonia because reserves are important. However, as shown by Mudd [77], the island could experience degrowth, forced by the depletion of fossil fuel resources and environmental cost constraints. This would further increase the economic and metabolic unbalances of the island. Furthermore, this situation will not eliminate local, long-term environmental impacts linked to existing stocks. We must now consider reducing these impacts and, at the same time, repairing environmental damage. This is an ambitious future research objective.

A possible nexus of minerals for the construction sector could be added to the one of metal - energy, by recovery of nickel slags. It could be globally positive if it fulfills several conditions. First, it should reduce the dependency of the island on imports of minerals that are indirectly responsible for one third of greenhouse gas emissions. A deeper analysis of imported minerals, and their use, should be conducted to estimate how recovered nickel slags could become a substitute for them. Second, nickel slag recovery should contribute to reducing the global contribution of the island to both

climate change and local pollution. The carbon footprint of various recovery possibilities should be assessed using Life Cycle Assessment, combined with Material Flow Analysis, to ensure the match between products obtained from nickel slag recovery, and local and closest foreign markets. Obviously, increasing transportation by exports of products recovered from nickel slags, possibly balanced by decreasing transportation of mineral imports, should be accounted for at the territorial level to assess the carbon footprint. Furthermore, the economic value of products issued from slag recovery is a crucial factor for the assessment. If there is no market for these products, there can be no hope of addressing imbalances in the island's metabolism. This global assessment is precisely the objective of the carboscories and carboval research projects studying the possibility of nickel slag recovery and using a mineralization process enabling CO2 capture [78]. Third, local actors should be involved and take part in the strategic changes to come, in order to ensure that they can benefit from possible long-term evolution. Indeed, there is a strong risk of consolidating an economy based on the extraction of nonrenewable resources.

Finally, New Caledonia perfectly illustrates the metabolic challenges of small extractive islands. These small extractive islands have political economy issues in common because their metabolism reinforces their social, environmental, and economic vulnerabilities. As Anke Schaffartzik and Melanie Pichler point out [79], the role of extractive economies needs to be better understood by identifying synergies and trade-offs in the use of global resources. This is an issue of coupling approaches in political ecology and social ecology, in order to provide biophysical and socio-political conceptualizations within the interdisciplinary sustainability sciences. The "metal-energy-construction mineral" nexus has made it possible to grasp the complexity of the flow circulation and its environmental consequences. In this respect, this method makes it possible to enrich knowledge on the sustainable metabolic transformations of small extractive islands.

**Author Contributions:** Conceptualization, formal analysis; J.-B.B., P.H., A.V., N.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors gratefully acknowledge funding from the "Agence calédonienne de l'énergie" (New Caledonian energy agency) and ADEME (French environmental agency), contract "Carboval" research project.

**Acknowledgments:** We want to thank the stakeholders that we interviewed and the reviewers for their valuable comments.

**Conflicts of Interest:** The authors declare no conflict of interest.
