GHGs - WITCH
|Model Documentation - WITCH|
|Institution||Fondazione Eni Enrico Mattei (FEEM), Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC)|
|Concept||Hybrid: Economic optimal growth model, including a bottom-up energy sector and a simple climate model, embedded in a `game theory` framework.|
|Solution method||Regional growth models solved by non-linear optimization and game theoretic setup solved by tatonnement algorithm (cooperative solution: Negishi welfare aggregation, non-cooperative solution: Nash equilibrium)|
Energy-related and land-use CO2 emissions have a detailed representation in the WITCH model.
Non-CO2 GHGs are important contributors to global warming, and might offer economically attractive ways of mitigating it. WITCH models explicitly emissions of CH4, N2O, SLF (short-lived fluorinated gases, i.e. HFCs with lifetimes under 100 years) and LLF (long-lived fluorinated, i.e. HFC with long lifetime, PFCs, and SF6). We also distinguish SO2 aerosols, which have a cooling effect on temperature. Since most of these gases are determined by agricultural practices, we rely on estimates for reference emissions and a top-down approach for mitigation supply curves. For the baseline projections of non-CO2 GHGs, we use EPA regional estimates (EPA, 2012). The regional estimates and projections are available until 2020 only: beyond that date, we use growth rates for each gas as specified in the IIASA-MESSAGE-B2 scenario, which has underlying assumptions similar to the WITCH ones. SO2 emissions are taken from MERGE v5 and MESSAGE B2: given the very large uncertainty associated with aerosols, they are translated directly into the temperature effect (cooling), so that we only report the radiative forcing deriving from GHGs. In any case, sulphates are expected to be gradually phased out over the next decades, so that eventually the two radiative forcing measures will converge to similar values.