Ok so there's no value for a transaction, but rather for a block.
However,many miners compete for a block, is this accounted for or is the number an average for the winning miner?
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).