I’m not sure if there’s a good way to measure how much CO2 is used to enforce fiat, but I very strongly suspect that it’s nowhere near as much as Bitcoin requires per economic unit or whatever. Bitcoin’s already using several country’s worth of CO2 and it’s still (compared to fiat) very fringe.
Also bear in mind that much of that CO2 generated by the force you’re describing, aside from the people guarding the banks directly, is amortized across all the other things that force guards. Even if fiat were replaced by Bitcoin overnight almost all of it would still need to be around.
Bitcoin doesn't use several countries worth of CO2. It has been "calculated" that "cryptocurrency" uses as much electricity as a small country. But that is not Bitcoin. Bitcoin does not use GPUs to mine. They use specialized chips which are far more efficient than GPUs. Etherium is the currency burning all the electricity. Also, you are conflating CO2 with electricity. Which is not correct in my opinion because electricy can generated via nuclear, wind and solar. In fact,any miners migrate to those power generation modes because it's cheaper for them. Electricity price is part of the ROI of mining.
If Bitcoin were a country, on its own, it'd be ranked 27th in the world on energy consumption. Looking at the chart there it very clearly uses as much energy as several countries (say: New Zealand, Hungary, and Peru) put together.
Also bear in mind that much of that CO2 generated by the force you’re describing, aside from the people guarding the banks directly, is amortized across all the other things that force guards. Even if fiat were replaced by Bitcoin overnight almost all of it would still need to be around.