https://orcid.org/0000-0001-8479-8686
Authors of the well-known 1972 book ‘The Limits to Growth’ had suggested that there are simply not enough resources and environmental capacity of our Earth to permit continuous growth. That stark assessment is still valid in 2021, even after decades of scientific advances and technological innovations. Since then the world population has doubled to 7.7 billion in 2020. It is projected to reach 9.7 billion in 2050 and nearly 11 billion around 2100. Fulfilling their demand for improved standards of living requires natural resources estimated to exceed the equivalent of three Earths or more!
The situation is accentuated by the undesirable climate change attributed to anthropogenic global warming greenhouse gas (GHG) emissions. Most countries have pledged net-zero emissions by 2050, and yet they are without exception lagging behind in meeting their respective commitments since the Paris agreement of 2015. Corporations have also made decarbonization commitments by a certain point in time, and they are accused of greenwashing. The focus of numerous climate meetings has been on why change is needed, and what targets and objectives can be set. However, none of them indicated concrete plans on how to get there. Obstacles include lack of (a) an internationally recognized carbon footprint measurement system, (b) international consensus on what constitutes decarbonization, and (c) acceptable rigor and independent verifiability. Common threads are energy efficiency, renewable energy, and reforestation. Unfortunately, they are sidestepping materials in the equation to meet net zero emissions and supporting the growth needs.
About 23% of global GHG emissions in 2020 are attributed to materials production. In 2015, the materials related emissions are 11.5 gigatons, which is 130% more than that in 1995. The domestic materials consumption per capita rose from 8.7 metric tons in 2000 to 12.2 metric tons in 2017 around the world. Correspondingly, the global materials footprint increased by 70 per cent. The global materials demand is projected to increase from 84 billion tons in 2015 to 184 billion tons by 2050. Humanity generated about two billion tons of solid waste in 2016 and projected to increase to 3.4 billion tons by 2050. Scientists are now modeling the environmental and health/social costs of materials. For example, the GHG emissions in the production process, health impacts, and waste management costs of plastics produced in 2019 alone could be 3.7 trillion dollars. Therefore, countries as well as corporations must specify materials production reduction targets as well as consumption reduction targets to accompany decarbonization targets in respective climate actions.
UN SDG12 and global think tanks advocate the now popular circular economy model for sustainable future. Is it alone sufficient to circumvent the limits of Earth to permit continuous growth? Let us delve via a widely used material, plastics. Materials Circular Economy fosters a healthy living environment and a circular economy via elimination or reduction of materials as well as resource wastage, GHG emissions, and raw materials/resources depletion. In the materials circular economy, the materials and products are purposely designed with lower environmental footprint and social costs, and higher circularity while satisfying the cost as well as functional requirements. In other words, one of the tenets of circular economy is prevention and reduction of materials use. There are limits to this tenet as evidenced by the essential role of plastics in dealing with COVID-19 pandemic. The world generates about 300 million tons of plastic waste every year. About 9% is recycled, 12% is incinerated, and 79% is accumulated in the nature. Improved waste management methods certainly will enhance the recycling rates, and lower the demand for virgin materials. However, considering the diversity of plastics, it is difficult to achieve higher rates of recycling. Inherent molecular arrangements of thermosets make them hard to depolymerize for recycling. Thermoplastics can be recycled but suffer from the loss of properties due to recycling processes, thus limiting the number of times they can be recycled. Circular economy envisions recycled materials to be used in the same applications. In reality, recycled materials are often downgraded to lesser demanding applications. Fundamental research at the scale of molecules is necessary to purposely design plastics for higher circularity. Majority of plastics in use are produced using chemicals derived from polluting and nonrenewable sources such as oil, natural gas and coal. Substituting them with plastics made from renewable sources is an option; while they are gaining market share, scientific research is needed to improve their range of properties, durability, and cost competitiveness. Furthermore, their environmental footprint should prove to be better than conventional plastics.
Plastics can be reused, repaired, remanufactured and repurposed to a certain extent. Perpetual use of plastics is not feasible as their properties deteriorate upon exposure to weather, in addition to wear and tear of use. Mechanical and chemical recycling methods have to be substantially improved to reduce their energy penalty and also to enable upcycling. We must also scale up novel alternative solutions such as microbial-assisted valorization and other environmentally benign processes. The tradeoffs between recyclability/circularity and environmental footprint of materials must be more clearly understood (see ). Advances at the atomic and molecular scales are necessary for producing plastics that are free from harmful chemicals, and to eliminate generation of microplastics and nanoplastics, which pose adverse impacts on human health and environment. In other words, substantial efforts are necessary to realize the circular economy of plastics.
Figure 1. Management of plastic waste.
Circular economy must be augmented with many other measures for sustainable future. For example, greater efficiency in industrial processes will lower the material footprint by ten percent. Further gains can be realized by optimizing the interdependencies across industry and economies. Traditional construction materials such as wood, timber, straw and mud have lower embodied carbon intensity than aluminum, steel, glass, and cement; embodied carbon of building materials indeed accounts for eleven percent of global GHG emissions.
It is also necessary to update materials curriculum at thousands of universities worldwide. Current curricula focus on interdependent aspects of materials science, namely, processing, structure, properties, and performance. Materials education should also include sustainability aspects, embodied carbon, operational carbon, environmental footprint, life cycle thinking, and social impact.
Materials have a substantial role in our climate actions to ensure sustainable future. Humanity must make continuous effort to minimize resource consumption and environmental impact as our planet has hard limits in terms of what it can provide and endure.
College of Design and Engineering
National University of Singapore
Singapore
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