A counterpoint to this argument Andreas Antonopoulos made in this video clip:

One key point he makes is that the energy consumption of the Bitcoin network is easy to calculate (transparent), while the energy consumption of the current financial system (servers for fraud-detection of credit card transactions, office space and infrastructure for customer support call centers, etc.) is hard to calculate, but could easily be just as expensive (energy-wise)

Additionally, for many green power sources, there's no way to "turn them off" other than waste the power or store it in batteries if the demand for electricity by the grid is low at the moment. Since batteries aren't perfectly efficient, Bitcoin mining could serve as a use for that excess power; "store" that energy in Bitcoin by running mining rigs with whatever excess power the electrical grid doesn't need from a given green power plant.