Assessing environmental sustainability using ecological limits expressed as mass flowrates with the inclusion of a sustainable time perspective

This study explores the concept of ecological limits (ELs) for determining the sustainable extraction of natural resources and sustainable discharge of emissions. ELs are expressed as limiting mass flowrates and equations are developed and presented for their quantitative estimation. These include a sustainable time perspective term. This is a time duration that provides sufficient time for humans to adapt to the depletion of a resource stock or emission budget, e.g., the time for a number of human generations. Thus, even if a resource is utilised at a greater rate than its regeneration rate, it could be considered sustainable if the resource extraction rate is adjusted so that the stock continuously lasts for more than the sustainable timeframe. The application of this ecological limits concept is illustrated by applying it to assessing the environmental sustainability of global fossil fuel energy, specific water resources, and global fertilisers. Exceeding ELs can act as a warning signal and highlight those resources and emissions where actions need to be taken to bring their extraction and discharge rates to within the ELs.