Add CEDS variable-aggregation mapping

[danielhuppmann]

This PR adds a mapping from the standard emissions variable tree to CEDS categories, per some discussion with @jkikstra

One complicated issue is the handling of transportation-emissions, where domestic aviation is part of "Emissions|*|Energy|Demand|Transportation" in the IAMC convention but part of "Aircraft" in CEDS.

@jkikstra suggested simply doing "Tranportation minus Domestic Aviation", but including computation-instructions goes against the spirit of a well-readable mapping.

Instead, I added two variables

• Emissions|CO2|Energy|Demand|Transportation|Road
• Emissions|CO2|Energy|Demand|Transportation|Other

that are not yet included in the variable template.

To be discussed further bilaterally.

FIY @IAMconsortium/common-definitions-emissions

[robertpietzcker]

Hi Daniel, maybe I am overlooking something obvious, but I am currently wondering what would be reported under "Other" if "Domestic Aviation" has a separate variable?

[danielhuppmann]

what would be reported under "Other" if "Domestic Aviation" has a separate variable?

This is a fix for now while I develop the CEDS-rename-aggregation tool, because some scenarios only report some of the transportation detail, so simple aggregation doesn't work. So I intend to do something like

0. Compute "Transportation|Other" as "Transportation" minus "Transportation|Domestic Aviation"
1. Use the mapping above to compute the CEDS variables
2. Drop the "Transportation|Other" variable from the scenario

[robertpietzcker]

thanks for the explanation - sounds good!