We've talked before on readings about how fixing the carbon footprint of the blockchain is a technico-moral imperative. Recently stumbled across this project, which seems to be at least using the right buzzwords. Curious to see if they have the math to back it up or not... they have no white paper on their website, but I think they can probably pull it off with some luck. Or at least, such is my hope, given my love of the blockchain and my love of a human-habitable planet.