"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"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)
"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.htmlhttps://www.sciencedirect.com/science/article/abs/pii/S2542435119302557"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.htmlEthereum and Litecoin are more energy efficient:
"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