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How the choice of multi-gas equivalency metrics affects mitigation options: The case of CO2 capture in a Brazilian coal-fired power plant

M.C.P. Moura, D.A.C. Branco, Glen Peters, A.S. Szklo, Roberto Schaeffer

This study shows how the assessment of emissions reductions from CO2 capture is critically dependent on the choice of multi-gas equivalency metric and climate impact time horizon. This has implications for time-sensitive mitigation policies, in particular when considering relative impact of short-lifetime gases. CO2, CH4 and N2O emissions from a coal-fired power plant in Brazil are used to estimate and compare the CO2-equivalent emissions based on standard practice global warming potentials GWP-100 with the less common GWP-50 and variable GWP for impact target years 2050 and 2100. Emission reductions appear lower for the variable metric, when the choice of target year is critical: 73% in 2100 and 60% in 2050. Reductions appear more favorable using a metric with a fixed time horizon, where the choice of time horizon is important: 77% for GWP-100 and 71% for GWP-50. Since CH4 emissions from mining have a larger contribution in the total emission of a plant with capture compared to one without, different perspectives on the impact of CH4 are analyzed. Use of variable GWP implies that CH4 emissions appear 39% greater in 2100 than with use of fixed GWP and 91% greater in 2050.

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