Bitcoin mining is likely responsible for 10‑20 Mt CO2 per year, according to a report released by the International Energy Agency
Source: https://cointelegraph.com/news/iea-report-bitcoin-causes-003-006-of-global-co2-emissions
IEA Report: Bitcoin Causes 0.03%-0.06% of Global CO2 Emissions
July 23, 2019
CoinTelegraph