Metrics Poster 3.pptx

technologies (a-c). The impacts of technologies with high CH4 emissions change significantly over time. The impact of CNG is initially lower than that of gasoline but exceeds this impact in 1-2 decades using the ICI (2-3 decades under a low leakage scenario). The impact of algae biodiesel (with methane leakage from a biodigester) exceeds that of corn ethanol in approximately 2-4 decades using the ICI or CCI. The impact of natural gas for electricity remains lower than that of coal, but increases from half the climate impact of coal to about 3⁄4 of its impact. Motivation Technologies emit varying quantities of multiple gases during their life cycles, including CO2 and CH4, and these gases have differing radiative properties and lifetimes (a). As a result, the impact of using a technology decays over time at different rates, as the comparison of gasoline and natural gas for vehicle transportation illustrates (b). Standard approaches use the global warming potential (GWP) to evaluate technologies on the basis of their integrated radiative forcing impact from the time of use to some fixed time in the future. Depending on the time horizon selected, the relative climate impacts of technologies can appear dramatically different, as the case of gasoline and natural gas illustrates (using 100-year (c) and 20-year horizons (d)). Here we formulate metrics to compare gases based on their time of emission, compare these metrics to the GWP in global and sectoral tests, and apply the new metrics to evaluate energy technologies with high CH4 emissions.1 Climate impacts of energy technologies depend on emissions timing J. E. Trancik* and M. R. Edwards, Engineering Systems Division, Massachusetts Institute of Technology *[email protected]