A number of different energy- and climate-related policies are, depending on the scenario setup and the research question addressed, explicitly represented in . This includes the following list of policies:
- GHG emission pricing
- GHG emission caps and trading emission allowances
- Renewable energy portfolio standards (e.g., share of renewable energy in electricity generation)
- Renewable energy and other technology capacity targets
- Energy import tariffs
- Fuel subsidies and micro-financing for achieving universal access to modern energy services in developing countries (via linkage to the MESSAGE-Access model)
- Air pollution legislation packages (fixed legislation, current and planned legislation, stringent legislation, maximum feasible reduction via linkage to the GAINS model)
In general, these policies are implemented via constraints or cost coefficients (negative and positive) in the optimization problem (see Section policy for more details). In the case of air pollution policies, the different legislation packages are implemented via a set of emission coefficients and associated costs derived from the GAINS model. The cost coefficients are, however, not part of the optimization procedure, but instead allow an ex-post quantification of air pollution policy costs for a specific energy scenario.