The following sources were cited in SAP Digital Futures Issue 35: Threat and Opportunity: Blockchain’s Hunger for Power.

By 2025, computing will use 20% of the world’s electricity and generate 5.5% of its carbon emissions.
‘Tsunami of data’ could consume one fifth of global electricity by 2025, The Guardian, December 11, 2017. https://www.theguardian.com/environment/2017/dec/11/tsunami-of-data-could-consume-fifth-global-electricity-by-2025.

Data centers are still 80% powered by fossil fuels.
‘Tsunami of data’ could consume one fifth of global electricity by 2025, The Guardian, December 11, 2017. https://www.theguardian.com/environment/2017/dec/11/tsunami-of-data-could-consume-fifth-global-electricity-by-2025.

Global power consumption is projected to triple by 2023.
‘Tsunami of data’ could consume one fifth of global electricity by 2025, The Guardian, December 11, 2017. https://www.theguardian.com/environment/2017/dec/11/tsunami-of-data-could-consume-fifth-global-electricity-by-2025.

If blockchain were a country, it would rank 39th in the world for energy consumption.
Bitcoin Energy Consumption Index, Digiconomist. https://digiconomist.net/bitcoin-energy-consumption.