Two emissions scenarios need to be selected for MAGICC to run. These are termed the Reference Scenario and the Policy Scenario, although they may well both be non-Policy or Policy scenarios. MAGICC comes installed with a library of pre-defined emissions scenarios, and with two scenarios selected as defaults: Reference = A1B-AIM; Policy = B2-MES. The full set of complete SRES 'no-climate policy' emissions scenarios are given in this library. To distinguish the six illustrative scenarios from the other 29, a hyphen is used (e.g. as in 'A1B-AIM'). In addition to the SRES scenarios, a representative no-climate-policy scenario is given (P50) constructed using median values for the full SRES set. Ten 'policy' scenarios are also given, labeled xxxNFB and WRExxx. These give CO2 emissions that will lead to concentration stabilization following the standard WRE concentration stabilization pathways, at level 'xxx'. The WRExxx scenarios will stabilize if the default case in which climate feedbacks on the carbon cycle are included. The xxxNFB cases will stabilize if these climate feedbacks are turned off (which is how the original WRE results were obtained). The baseline scenario used for calculating these stabilization cases is the P50 scenario, so the concentration profiles do not precisely match the original WRE profiles. The names of these scenarios are listed when you choose Emissions Scenarios in the Main Edit Menu. To select from this list and choose your own Reference and Policy scenarios, clickon the required scenario and then click on either the Reference or Policy arrow to load the chosen scenario into MAGICC.
If you need to edit one of the existing scenarios or add to the scenario library, go to the MAGICC subdirectory, copy one of the *.GAS files to a new file with an appropriate filename (Maximum 8 characters; e.g., NEWSCEN.GAS) and then edit this new file using your favorite editor. The new scenario will automatically appear in the library list.