Of the things killing the planet, I don't think Bitcoin is high on the list. Overall, I think block chain is a fascinating and useful technology that certainly has application in the world of finance.<p>However, I strongly question the need to perform the mining operation inherent in nearly all cryptocurrencies. Money needs to certainly needs to fulfill its roles as a medium of exchange and store of value, but there are potentially more efficient and effective ways to do so.<p>The most compelling proposal I've seen is Bob Blain's Hour Money model (hourmoney.org). Developing a time-based block chain that equates global labor time to an international unit of measure that would serve as our money seems like a better direction.