So transactions on exchanges are less wasteful?
A deposit from wallet to exchange generates the same pollution?
Or is it "only" mined transactions? Does the transaction size matter?
reward_per_block * price = value_per_block
cost_per_hash * avg_hashes_to_find_block = cost_per_block
cost_per_hash is the cost of electricity and mining hardware . If value_per_block > cost_per_block, mining is profitable and more miners will join the network, increasing avg_hashes_to_find_block, until value_per_block == cost_per_block.
co2_emissions = avg_hashes_to_find_block * co2_per_hash.
So the emissions are a function of the price of bitcoin and the price of (electricity + mining hardware).
(This is obviously not quite apples for apples, since you'd also have to account for VISA & Co. likely employing more people than Bitcoin, on the other hand, Bitcoin also requires absurd amounts of throw-away hardware.)