Conversion of climate metrics for policy applications

Description

Abstract (English)

When assessing CO2 and non-CO2 climate effects of anthropogenic emissions from transport sectors, e.g., aviation emissions, a physical climate metric needs to be selected. In addition, climate metrics are required to to calculate CO2-
equivalent emissions for integration of non-CO2 effects in legislation or cost-benefit analysis. However, since various metrics are currently in use, it is desirable to have conversion factors available which allow to convert from one metric to another. The widely discussed choice of climate metric is not impeding any further steps, such as cost-benefit analysis or risk-assessments of aviation climate impacts as the here presented conversion factors are enabling an alignment in a downstream process. Here, we establish the relation between radiative forcing, measured in W/m2, and any other physical climate metric with the help of the climate response model AirClim. AirClim delivers temporal evolution of radiative forcing and temperature changes for specific emission developments (constant, pulse in 2025, lifetime 30 years, and business as usual). We provide conversion factors for individual non-CO2 climate effects, which allow to convert to global warming potential (GWP), efficacy weighted global warming potential (EGWP), relative average temperature response (rATR) or global temperature potential (GTP) over three distinct time horizons of 20, 50 and 100 years. For increasing emissions, the point in time when CO2 effect becomes dominant over non-CO2 effects, is shifted later in time when compared to decreasing emissions. For constant emissions and 100 years time horizon the non-CO2 to CO2 ratios lie between 0.7 and 2.9 depending on the physical climate metric applied. Application of these precalculated conversion factors allows to perform conversion between various metrics without running a climate (response) model.