The idea that mining is a waste is a bit strange to me - of course it is a waste, that is the genius insight of it all. Waste is the most powerful thing, it is pure cost, the hardest thing to do, raw sacrifice. There are no tricks or shortcuts to over-taking the blockchain, just pure cost and waste. If the proof-of-work had value and could be sold, it would make the network less safe, and less predictable, subject to the whims of the market for its output, and able to fund its attackers while they attack. Proof-of-work is a nice way of saying proof-of-waste.
There are other types of consensus mechanisms, like proof-of-stake, that are much more energy efficient, with their own set of pros and cons. They should, and will, exist; but there will still always be at least one proof-of-waste blockchain. Waste is the gold-standard of expense.
The environment issue is a societal one. We need to move to clean energy, and we are.