I’m no expert, but sounds like you are over your head. I’d suggest to bring in any number of consultants who are pros at doing this sort of thing, figuring out C2G costs, total revenue expenditures vs. savings, carbon offsets, etc. esp. for a large company, they must have the deep pockets if they expect to get any useable report out of an endeavor like this.
The key to any job is knowing what you know and knowing what you don’t. From what you posted so far, this is far in the realm of stuff you don;t know so better to bring in someone who does and then lay the responsibility on them rather than taking it up yourself only to have the responsibility on your shoulders. Bringing in a consultant should not be looked at as a point of weakness, rather than a point of strength in identifying those areas you are smart enough to identify where you need professional experience and the value that comes with it.
R