Idea: Change BTC protocol to include a new field in coinbase transactions documenting the CO2 emissions of each block. Introduce an uncle block reward like ETH. Miners agree to audits of their reports. Make block reward dependent on carbon emissions. Use rest for offset programs.
Why not just use proof of stake and get it of all the useless nonce-calculations?
Bitcoin are being traded by energy companies to subsidize their infrastructure and improve energy efficiency and capacity.
In some ways Bitcoin is a battery, because hydro dams don't idle generators as often they can sell their excess energy production and subsidize the dry season. Oil companies capture the natural gas flares and use it to power generators to mine bitcoin, etc. There really only needs to be one POW coin, and I think it's pretty obvious that Bitcoin is it.