Does that mean Ethereum could be made carbon neutral at a cost of $2m per day to buy $100 per tonne carbon offsets? I wonder if such a policy could be implemented at the protocol level.
Real change should come from a reduction first, then offsetting what you can't reduce (until you can). So, in theory, yes. And probably for much less even, because there is still a lot of lower-priced carbon credits/offsets that are totally valid.