It was a massive shock to me too when I first heard about it. Right now, I think the cryptocoin economy creates more CO2 than Argentina (BBC).
But, not Hive! As I understand it, it's footprint is so small as to be practically negligible. /but I'll have to drag up the numbers at a later point, and I'll put it in blog post :)
RE: Why Hive is such a great place for artists