These figures are necessarily approximations but not without justification. We use the following figures for the calculations:

Power consumption per MN = 21.6 Watts

Power consumption per SN = 10.8 Watts

Cost per kWh = $0.19

CO2 generated per MWh = 346 kg

We assume the worst possible case where all the power is generated in coal-fired powerstations. The figure of 346 kg per MWh comes from Intergovernmental Panel on Climate Change (IPCC). Guidelines for National Greenhouse Gas Inventories (2006).

In May 2020 the Bitcoin network consumed approximately 4.72TWh of electricity. Source: Digiconomist

Using the same worst-case all-coal production scenario it would have produced 1,633,120,000 kg of CO2 in just one month. The Bitcoin network consumes more electricity processing 1 transaction than the Crown network consumes in a whole day.