Hi everyone :) This is from some new research I just published. You can read about the full methodology in this 22-page writeup[1] and I also made a tracker [2].

[1] https://github.com/kylemcdonald/ethereum-emissions/blob/main...

[2] https://kylemcdonald.github.io/ethereum-emissions/

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.