In Bitcoin mining, price follows hash power and vice-versa like chicken and egg. The halvening will effectively halve the mining reward per block. In the past these events haven’t had much significance on the dollar value of the overall reward per block. However, because fewer coins are rewarded post halvening, the dollar price per Bitcoin effectively doubles (not immediately, in reality the dollar price rises over the prior months in anticipation of the halvening event).
So in all, the longer that Bitcoin survives, one would expect hash power to increase exponentially. However, I agree that the electricity usage problem is hugely overblown and is used by Bitcoin sceptics as another excuse to bash the technology through misinformation. In reality, as Bitcoin gets harder to mine because global collective hash power is surging, mining ops are increasingly migrating to renewable sources. e.g. hydroelectric in Canada and geothermal in Iceland (one of world’s largest mining facilities is there already). This is market forces at work, driving the requirement for more energy efficient mining, just as you would expect over the long-run.