For crypto to become greener, I think it needs to address several points. First, as far as I know, not all consensus mechanisms are equally energy efficient. I think proof of work performs much worse than proof of stake or proof of personhood, for example. Changing that would be a possible first step. Ethereum is planning to switch from proof of work to proof of stake. I am curious to see how and when this will be implemented. And whether other cryptocurrencies will be motivated to take this step as well.

A second starting point would be that only sustainable electricity should be used for cryptocurrencies. If the energy used can be covered by renewable energies, a lot would be gained. You just have to make sure that this green electricity is not lacking elsewhere.