By considering the environmental impact of materials through their whole life cycle, materials scientists can help develop more sustainable alternatives.
Global warming is a fact — the joint efforts of researchers worldwide and the reports of the Intergovernmental Panel on Climate Change have clearly evidenced connections between the amount of anthropogenic greenhouse gas (GHG) emissions and the global surface temperature increase from preindustrial levels1. Guided by this scientific evidence, the Paris Agreement — which, despite President Trump's short-sighted U-turn, is still supported by the vast majority of the countries that attended the 2015 United Nations COP21 Summit2 — has set targets to cut GHG emissions in order to keep the rise in temperature expected by 2100 well below 2 °C. A swift transition to low-carbon energy technologies is the main path to achieve this aim3,4, yet other routes are also available for materials scientists to contribute to this ambitious goal.
In fact, the way materials and commodities — from food and water to metals, coal and oil — are managed during each step in their life cycle has an effect on the environment (on both global and local scales), economic development and the well-being of the world population. Therefore, these resources should be controlled wisely to ensure a sustainable development of our planet — that is, in the words of the 1987 United Nations report Our Common Future5, the “development that meets the needs of the present without compromising the ability of future generations”.
In this issue of Nature Materials, we have explored some of the environmental challenges related to key commodities such as concrete, the most widely used building material, and metal alloys, whose mechanical properties are leveraged to fabricate lightweight and resistant components for applications ranging from prosthetics to aerospace6. On page 698, Paulo Monteiro, Sabbie Miller and Arpad Horvath outline the approaches that are being adopted to reduce GHG emissions and energy use in concrete production and to extend the lifetime of concrete infrastructures. Xiuyan Li and K. Lu on page 700 propose the engineering of defects and dislocations as a strategy to tune the strength and ductility of steels and other metals. As an alternative or in combination with alloying, this approach may simplify the overall composition of high-performance metals, making them less dependent on elements in short supply and more easily recoverable at the end of life.
But how can we actually measure the benefits of this or other approaches on the environment, and guide materials producers in deciding the manufacturing processes to be preferred? In a Commentary on page 693 of this issue, Randolph Kirchain, Jeremy Gregory and Elsa Olivetti describe one of the tools used to quantify the environmental burden of a material or a technology — life-cycle assessment. Using indicator scores that numerically convert the resources used and the pollutants released during all activities (including fabrication, use and end-of-life) into measures of impact (such as global warming potential or ecotoxicity), an environmental life-cycle assessment is able to determine an overall product impact (pictured). Moreover, this method allows a quantitative comparison of the effects of material or process changes on various aspects of environmental impact, and as such it is now becoming widely used by regulatory agencies to assess the large-scale benefits of new products or manufacturing approaches. Yet, Kirchain and colleagues warn about some key aspects — such as the specific functional unit defined as the target of the study, the specific set of activities considered during the various phases of the product life and the way in which primary and recycled resources are accounted — that are unavoidable sources of uncertainty, and therefore should be carefully described in each analysis to ensure a fair comparison between alternative materials or technologies. The implementation of comprehensive databases collecting information about all the activities relevant to a product life cycle and their environmental impact is time- and resource-consuming, yet it is a necessary step to improve the effectiveness of this assessment.
However, the use of any metric alone cannot provide a complete picture of the implications of materials choices on other sustainability issues such as resources management, biodiversity preservation, poverty eradication and fair individual and societal development. Therefore, the information provided by environmental life-cycle assessments should be integrated with economic and social analyses to help researchers understand the broader impact of a material or a technology. Developing complementary tools that enable such a holistic assessment is certainly another interesting challenge where materials scientists can contribute, and which may be key to identify the most sustainable pace of development for our society.