Thanks for the response and analysis. I think I have qualms with how mrb exaggerates the difference in their conclusions. He says Alex' numbers are "rather inflated" and has told me before that Alex makes "fundamentally flawed assumptions" and has "holes and flaws" in his logic, when really when you look at the difference in their forecast it's 0.5% versus 0.4%... both numbers support the general idea that assuming the technology brings no efficiency to society, Bitcoin is an environmental catastrophe.
Alex's BECI model claims Bitcoin currently consumes 7.6 GW. Whereas this paper is more reasonable and states the future consumption might grow to 7.6 GW by the end of 2018. These are 2 very different statemetns. What I call "fundamentally flawed" is the BECI claim, not this paper.