A climate goal–based, multicriteria method for system evaluation in life cycle assessment

Abstract

Our ability to restrict global warming to the established objectives in the Paris Agreement depends on the metrics used to evaluate the climate change impact. Stemmed on the criticism of the current GWP metrics used with life cycle assessment (LCA), this study proposes new indicators and an interpretation grid for climate change impact in LCA, which are adaptive to present, short-term, and long-term climate goals. The global mean temperature change (GMTC) is used in the indicators’ definition and time parameters are introduced for a multicriteria evaluation of climate change impact. We adopt calendar-related time targets instead of a fixed time horizon. The systems are analyzed on a real-time scale and with respect to a climate-target point in time (for example, 2050 as objective for climate neutrality), in contrast with conventional LCA. The objective is to provide flexibility in system evaluation, adaptable to current and future targets. Four indicators are introduced: (1) the amplitude of the temperature change (GMTCmax), representative for climate extreme events; (2) the time at which GMTC starts to definitely decrease and its distance with respect to the goal (tlast_peak); (3) the time climate neutrality is reached and its distance with respect to the goal (tneutral); and (4) the accumulated warming until a targeted time, representative for sea-level rise and ice melting (integrated GMTC at a given time target, for example at the end of century iGMTC2100). An analysis grid is proposed based on these indicators and illustrated on 26 emission profiles involving long- and short-lived greenhouse gases with various temporalities, as well as on two dynamic LCA case studies. In the group of neutral systems, temporality is responsible for variations in GMTCmax and iGMTC2100. Increasing the frequency of emission/capture events flattens both indicators and provides the best performance. Equal CO2 emission systems are discriminated primarily by tlast_peak, while in the case of methane, more relief is observed for all indicators. The method allows for the design of tailored mitigation solutions in LCA application examples. The indicators are able to discriminate and rank systems that are considered to be non-impacting, equivalently impacting, or neutral in LCA-GWP metrics. Such metrics is necessary to correctly (avoid strong simplifications) and unambiguously (with unaltered physical parameters, closer to climate physics) evaluate the effect on climate, mitigation solutions, neutrality, and support decision-making.