Quote

"Recent published estimates of bitcoins electricity consumption are wide-ranging, on the order of 20‑80 TWh annually, or about 0.1-0.3% of global electricity use"

https://www.iea.org/newsroom/news/2019/july/bitcoin-energy-use-mined-the-gap.html

Quote

"bitcoin mining is likely responsible for 10‑20 Mt CO2 per year, or 0.03-0.06% of global energy-related CO2 emissions."

(as of November 2018)

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"The corresponding annual carbon emissions range from 22.0 to 22.9 MtCO2 ... This level sits between the levels produced by the nations of Jordan and Sri Lanka"

https://www.iea.org/newsroom/news/2019/july/bitcoin-energy-use-mined-the-gap.html
https://www.sciencedirect.com/science/article/abs/pii/S2542435119302557

Quote

"Ethereum (ETH), the second largest cryptocurrency by market value, processes more than twice as many transactions as the bitcoin network while using only about one-third of the electricity consumed by bitcoin. ETH also operates on a Proof-of-Work (PoW) consensus mechanism"

https://www.iea.org/newsroom/news/2019/july/bitcoin-energy-use-mined-the-gap.html

Ethereum and Litecoin are more energy efficient:

Quote

"From 1 January 2016 to 30 June 2018, we estimate that mining Bitcoin, Ethereum, Litecoin and Monero consumed an average of 17, 7, 7 and 14 MJ to generate one US$, respectively. Comparatively, conventional mining of aluminium, copper, gold, platinum and rare earth oxides consumed 122, 4, 5, 7 and 9 MJ to generate one US$, respectively, indicating that (with the exception of aluminium) cryptomining consumed more energy than mineral mining to produce an equivalent market value."

https://www.nature.com/articles/s41893-018-0152-7