Put numbers on the sustainability

Sustainability is about meeting the needs of the present without compromising the possibilities for our future generations to meet their needs and is commonly perceived as comprising three dimensions – a social, an economic and an environmental dimension, e.g. in the triple bottom line thinking applied in many companies today. As engineers we need methods to analyze the sustainability performance of the technologies that we develop in order to create value for society. Quantitative methods allow us to benchmark alternative solutions against each other, to prioritize improvements and to document the sustainability performance. In this presentation the focus will be on the environmental dimension of sustainability and on methods for quantifying the environmental performance of products and technical systems. A product may cause environmental impacts when it is brought to use, but also when it is produced and disposed of at its end of life. The assessment therefore needs to take a life cycle perspective comprising all relevant activities from the extraction of resources over production, distribution and use, to the disposal and possible recycling of its constituents in new products (Figure 1). Figure 1. Product life cycle Environmental sustainability encompasses multiple types of environmental impact ranging from the global scale like climate change and stratospheric ozone depletion over regional impacts associated with air pollution impacts causing acidification, photochemical ozone formation and particle exposure of humans, to the local impacts associated with physical transformation of land and extraction of water. Chemicals can cause toxic impacts to humans and ecosystems on all scales. All these impacts need to be quantified if we want to put numbers on sustainability. The life cycle perspective on products and systems and the coverage of all relevant environmental impacts are combined in Life cycle assessment (LCA) which is introduced in the talk as the tool to put numbers on environmental sustainability. The basics of LCA are introduced, current applications are presented and a discussion of its possibilities and limitations in assessment of sustainability in relative and absolute terms is given.