(691d) Attributional to Consequential Life Cycle Assessment – Steps Toward a Unified Framework

Life cycle assessment (LCA) using well established attributional methods is narrowly focused on determining the environmental impact and properties of a technology or product by portraying it as an isolated entity and linearly scaling it up or down in size to match its demand. It doesn’t consider the introduction of this technology into society, its acceptance and the ripple effects that might occur due to such a technology in the real world. For example, introduction of a novel “green” technology might be obstructed due to lack of available resources, acceptance of its price by industries and consumers, and how competing technologies and products adapt themselves in response to its introduction into the market. Such a problem can be thought of as being analogous to a chemical engineering design problem in a laboratory (attributional LCA) versus a full-sized industry and its effect on the associated economy (real world impacts). In this sense, there are some gaps between engineering decisions based on technological excellence and market decisions based on the economy and human preferences.

One of the methods currently used to capture such cascading effects into the market and economy is Consequential LCA (CLCA). It accommodates the interaction between competing products in market, how prices affect the demand and supply of goods and also the incorporation of factor constraints. Even though around for two decades, the method has not matured fully. Different groups of researchers practice different flavors of applying CLCA, each with their own unique advantages and disadvantages. Broadly, the three methods are System expansion, Rectangular Choice-of-Technology, and Equilibrium modeling. System expansion and marginal technology based approach, first introduced by Weidema uses a hierarchical set of rules and decisions to determine competing products and technologies of the system in question and tries to determine in a logical fashion, how the consequences of incorporating this novel technology would propagate through the economy and society. Being a step-wise question and answer based approach, it is evident that the methods suffer from the problem of boundary cutoff and has a narrow scope of the extent of consequences considered. The Rectangular Choice-of-Technology (RCOT) framework has been developed to account for market effects as a form of economy and environmental resource (economy factor) constraints and multiple technology uses in analyzing economic systems. The RCOT framework could show gradual and partial adoption of alternative technologies to displace conventional ones as a consequence of market effects. However, the framework does not account for price changes of commodities due to changing market conditions. Equilibrium modelling is a different approach to CLCA, using the economic general equilibrium models to capture price effects, through supply demand elasticity values and microeconomic relations. They include microeconomic concepts such as price elasticities of supply and demand, market clearing constraints, production and consumption functions, maximization of profits of different agents in the model, such as government, investment agents, producers, household and foreign markets. However, the major drawback of using these models is that they are highly aggregated, making it difficult and uncertain to study the impact of a specific product or technology.

In this research work, we perform a broad comparison of these methods using the same case study and highlight the differences in scope, results and insights obtained from each method. We explore their advantages and disadvantages in detail. Such an exploration and comparison provides insight into the characteristics and benefits of each method. With the knowledge obtained from such an exploration, a CLCA based optimization framework that combines all the methods is suggested to give a novel multiscale solution. The equilibrium models in this framework will help in system expansion which reduces errors in system boundary selection while the marginal-based and RCOT approaches can be focused on processes where greater resolution and details are required. Along with that, the presence of third finer engineering scale enables designing of processes while performing CLCA, which is a novel approach in the Sustainable Process Design field that has typically used ALCA for determining environmental impacts.

Ref:

Ekvall, Tomas, and Bo P. Weidema. "System boundaries and input data in consequential life cycle inventory analysis." The International Journal of Life Cycle Assessment 9.3 (2004): 161-171.