Interesting numbers, OP.

There was another study which was shared on the forum just a few days ago, published by the University of Cambridge, which you can find here: https://www.jbs.cam.ac.uk/fileadmin/user_upload/research/centres/alternative-finance/downloads/2018-12-ccaf-2nd-global-cryptoasset-benchmarking.pdf. I would draw your attention to pages 81 onwards. Their raw numbers seem to agree with yours - they estimate between 52 and 111 TWh is used by mining the top 6 currencies, with bitcoin accounting for 75% of that (39 to 83 TWh), putting your figure of 54.6 TWh pretty close to the middle of that range.

Your links quote that as being 0.24% of the world's total electricity consumption, and the study I linked quotes it as less than 0.01% of the world's total energy production. Very interesting how a slight change in wording, which most readers would gloss over, gives such a drastic difference in percentages. Data can be always be manipulated or presented in such ways to give a bias towards what you want to prove.

The report I linked to suggests around 30% of mining energy is renewable, so that would have an effect on the final CO₂ numbers. It's perhaps also worth nothing that the metric of energy consumption/CO₂ production per transaction isn't the most useful, as the amount of energy spent on the bitcoin blockchain is independent of the number of transactions it is processing.