Bitcoin is the most efficient monetary network ever devised.
All mining efforts, from whatever energy source, go directly into securing the network. All hashes matter. All hashes count. None are wasted.
"Every Hash Is Sacred"
If a mass of new miners joins the network, the difficulty adjustment algorithm will automatically optimize the level of effort required for a block to be mined. This happens every two weeks (every 2016 blocks, to be exact).
If miners leave the network, the same adjustment algorithm will ensure that blocks are produced every 10 minutes, like clockwork.
No other system of money or value transfer, accounting, supply generation, or discovery could be more efficient or secure.
If bitcoin were not mined with SHA2 Proof-of-Work mining, then no money would be secure, no money would be safe, no money would ever be sound in this world of zeroes and ones.
This process of balancing hashes and blocktimes is one of many forms of incentives and methods inherent to the network that creates a digital bearer asset with final settlement that cannot be confiscated.
The same cannot be said of gold, although fairly limited in supply (not perfectly, mind you) – gold can be centralized, rehypothecated, and papered over in a way bitcoin cannot.
There are no gold full nodes to verify the supply or allow an individual to ascertain the genuineness and purity of the coins received either.
Gold mining also entails a lot of waste: Wasted effort, disasters, pollution, and of course raw energy expenditure.
There is no guarantee that the energy put into efforts to mine gold will produce anything of value.
With bitcoin, all mining efforts contribute to the total hash rate, and are accounted for in the regular, periodic difficulty adjustments to keep the supply schedule on-time and block times steady.
Bitcoin Energy is never wasted. Bitcoin Energy is forever.
Questions, comments? My DMs are open: @bc1984adam