The data of "coinshares" have proven to be wrong with the recent drop of 25% of hash rate caused by a global black-out in the province of Xijiang : a province of china running mostly (80%) on coal :

The data from the University of Cambridge is much more accurate and detailed :

Based on this data of shares per region, and on a database of life cycle assessment (ecoinvent) I show that the average carbon footprint of bitcoin mining is 830g CO2 / kWh : way worse than the US mix :

With the current consumption ( 140 TWh / year), this sums to over 115 Mt CO2 / year : more than the carbon footprint of whole Belgium !