> Does anyone else have good data on the incremental CO2 emissions from either of these?
Virtually none. Bitcoins get mined with or without transactions, as long as the expected block reward exceeds operating costs, work will be performed. The amount of transactions is fixed (or rather capped), transaction fees are a fraction of block rewards. By performing a transaction, you are bidding up the price for a transaction. Therefore, in aggregate, you are helping keep those miners in the game that are just about to become unprofitable.
Virtually none. Bitcoins get mined with or without transactions, as long as the expected block reward exceeds operating costs, work will be performed. The amount of transactions is fixed (or rather capped), transaction fees are a fraction of block rewards. By performing a transaction, you are bidding up the price for a transaction. Therefore, in aggregate, you are helping keep those miners in the game that are just about to become unprofitable.