To add, the energy devoted to Bitcoin hashing is a product of the bitcoin price, block reward, and the wide acceptance in the Bitcoin community of the idea that

To add, the energy devoted to Bitcoin hashing is a product of the bitcoin price, block reward, and the wide acceptance in the Bitcoin community of the idea that provable energy burn is a good way to ensure rarity of the coins. Even if we maintain proof of work chains as the fundamental consensus tech, there is absolutely nothing (aside from momentum) stopping the community from decreasing the block reward to the a lower value required to prevent double spends of reasonable size. The current hashing power and energy burn in Bitcoin is absurdly oversized for that specific purpose. You could even maintain the current coin issuance schedule - there is absolutely no need to burn coins into existence, you could simply distribute them randomly to existing holders.