Life cycle assessment (LCA) has become the most common approach for assessing and designing sustainable systems. Over the last two decades, this method has been standardized and is a convenient approach to quantify environmental impact of processes through the life cycle with the availability of inventories and ease of software use. The primary benefit of including life cycle considerations in engineering decisions is that it reduces the chance of unintended harm by shifting a problem outside the narrow boundary of traditional engineering. Thus, LCA considers the impact of emissions and resource use of activities that contribute to the selected product or process from “cradle to grave” .
However, using LCA to measure the environmental impact of systems and develop sustainable solutions suffers from several shortcomings. For example, LCA encourages decisions that do “less bad” instead of “more good” in the sense that since this approach only estimates the impacts of systems relative to other similar systems, processes that have the least impact are deemed sustainable. Furthermore, since LCA is a macro-level analysis, it can be difficult to make improvements for specific processes, particularly if most of the impact lies outside the boundary of the plant scale, along the supply chain or use phase of a product. LCA methods also ignore essential interactions with nature that provide ecosystem goods and services that are essential for sustaining human activities and well-being. Although efforts are underway to incorporate into LCA the impacts on ecosystem services and biodiversity due to land use and land use change in a spatially explicit manner , currently the role played by ecosystems in supporting engineering activities and the ecological limits imposed by these systems have been ignored. Eco-LCA ,  a tool that explicitly accounts for the ecosystem service flow across the life cycle of products bridges the gap between conventional LCA by extending the boundary of analysis to include ecological systems but does not capture ecological carrying capacity. The approach of cradle-to-cradle (C2C) design also attempts to overcome some shortcomings of LCA but this approach ignores life cycle aspects and the role of ecosystems.
The recently developed framework of Techno-Ecological Synergy (TES) attempts to overcome many of these shortcomings of LCA by explicitly capturing synergies between systems in technological and ecological spheres. Systems at multiple scales ranging from individual processes, supply chains and life cycles can be evaluated along with their relevant supporting ecological systems. Resource inputs to and emissions from technological systems create a demand for ecosystem services, while ecological systems have the capacity to sequester most of these pollutants thus supplying relevant ecosystem services. Absolute sustainability indices defined by Bakshi et.al 2015  based on the overshoot in demand for ecosystem services over its supply can be used to assess the level of sustainability of systems. This metric system is multi-scale in nature, ranging from local to global. For a process to be locally-sustainable, emissions within a local boundary should not exceed the amount that could be sequestered by the surrounding ecosystem. A necessary condition to be satisfied for reaching the goal of sustainability is to maintain the demand for ecosystem services within the supply at the largest scale applicable to the ecological system.
This talk will provide practical insight into the pros and cons of using the TES framework to assess the sustainability of a system. Application of the TES framework to determine the level of sustainability of a system compared to that of the LCA approach will be demonstrated by a book manufacturing system - a traditional paper book vs. a book designed by the C2C approach. The latter uses synthetic polypropylene sheets while the former uses pulp-based paper sheets. In the recycling stage, for traditional book, ink and paper cannot be separated easily, leading to down-cycling rendering both materials with lower qualities. On the contrary, synthetic paper in C2C books can be “up-cycled” and reused since the ink can be washed off easily. Designers have established that by closing this material loop for synthetic paper, the C2C book is expected to perform environmentally better.
In this case study, LCA and TES are applied to the production of both type of books to compare their environmental performances. From the LCA study, it can be inferred that C2C book have a larger environmental impact than the traditional book. However, analyzing the production process using LCA technique does not provide an insight into the absolute level of sustainability of these systems. For instance, even though traditional book production has comparatively less environmental impact, the resource input and pollutant emission might still be well-above ecological carrying capacity. In contrast, TES can provide more insights for absolute sustainability at selected technological scale and corresponding ecological scale. Taking carbon sequestration service as an example, at local scale, it can be inferred that the pulp-based paper production for traditional book is sustainable because the demand for carbon sequestration service is less than the ability of surrounding ecosystem to provide the service. Similarly, at local scale, the synthetic paper production for C2C book is unsustainable because the local demand for the service overshoots the supply from surrounding ecosystem. At life cycle scale, the demand for carbon sequestration service imposed by CO2 emissions due to a traditional book exceeds the amount that can be sequestered, mainly because of the inclusion of emission-intensive processes, such as electricity generation and book glue production. From this multi-scale analysis, we can identify processes with higher overshooting and make technological improvements accordingly. Moreover, by using the TES approach to design for sustainability, we not only have the option to reduce the resource inputs and emissions as with the LCA approach, but also the option of increasing the supply of ecosystem services that can be achieved by proper landscape planning. This solution might be potentially more cost-effective and environmental-friendly than its technological counterpart.
Even though TES approach can provide us with many useful insights, the practical feasibility of this approach is limited by the availability of detailed local production information and proper ecological models. The former is necessary to quantify the demand for ecosystem services within the local ecological boundary and the latter is crucial for better quantifying the supply of ecosystem services at different scales. With the development of geographic information system and remote sensing technology, more accurate quantification of ecosystem service supply and demand at selected scale can be achieved. TES approach can then provide absolute sustainability metrics at different scales and for various ecosystem services, which can facilitate decision-making at all relevant scales.
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