Document dimensions of historical_emission vs. EMISS

[ClaraLuisa]

The variable EMISS is defined over the set emission, the parameter historical_emission, however, is defined over the set type_emission. Would it maybe be more consistent to define both over the same sets?

[danielhuppmann]

Thanks @ClaraLuisa for this question!

The logic for keeping these two distinct was the following:

1. historical_emission is only used in the constraint EMISSION_CONSTRAINT so that it is possible to consider previous periods in the (average) emissions. Strictly speaking, this does not only cover "historical" data, but could be used when implementing a rolling-horizon approach or implementing shocks, i.e.,

• solve a scenario for the time period 2020-2100 with a constraint on average cumulative emissions
• fix the results by using Scenario.clone(shift_first_model_year=2040) (this should automatically assign the EMISS results to historical_emission for the years 2020 and 2030 - but I think this is not a tested feature)
• resolve the scenario with a tighter emissions constraint for the period 2020-2100

The idea was that this approach would be easier than having to calculate actual emissions in 2020 and 2030, subtract that from total allowed until 2100, add a new constraint 2040-2100 with that value...

2. Processing of results: the reporting of GAMS results should never use the historical_emission parameter, so it is not necessary to have that level of detail in the input data. If you want to have historical emission of individual species or baskets of gases, this should come directly from a timeseries-data file, not be processed via the scenario input data -> GAMS -> postprocessing pipeline.

Does that make sense? It might be useful to check whether this is tested, add a test if necessary, and update the documentation...

[ClaraLuisa]

Hey @danielhuppmann, thanks for clarifying. This now does make a lot more sense indeed.