If you ignore the costs of the trust issues between participants (as well as a lot of physical infrastructure apart of trust chains) and how that plays out through the entire system, and a lot harder to trace CO2 values on (esp those that people will all agree on).

Here's one persons take on this with Banks vs BTC wrt CO2[0] with their numbers from last year that I'm sure plenty of people will disagree with in one form or another (usually without numbers of their own).

[0] https://medium.com/@mukeat/carbon-footprint-differences-btc-...