This is definitely a lesson to me to include sources in footnotes - I think my source here was googling "energy usage ethereum transaction" and using the info card at the top of the search page, which appears to be from https://www.weforum.org/agenda/2017/12/bitcoin-consume-more-... and... is an outdated and not great source.

Noted that my numbers for Ethereum are almost certainly not correct, but I think the point still stands that "the carbon footprint of crypto and blockchains depends hugely on which blockchain you're talking about"