I actually address this point in my post: "Many/most miners use hydroelectric power because competition compels them to use cheap renewable energy instead of other polluting power sources such as coal power plants" examples:
BitFury: https://www.businesswire.com/news/home/20151211005837/en/Bit...
KnC: http://thenodepole.com/2015/06/04/kncminer-to-build-new-20mw...
Therefore your worry about CO₂ emissions is misplaced.
It is crazy to have a currency that requires this dumb make-work of hashing which results in CO2 emissions. We live in a world of dangerous climate change and Bitcoin users want us to expel CO2 into the atmosphere with every currency transaction. That is dumb and not sustainable.