https://www.theatlantic.com/technology/archive/2018/03/bitcoin-mining-arbitrages-cheap-electricity-into-money/555416/
The point, too, is that the scaling-up process cannot stop. That’s how the system has been built. Even if bitcoin mining’s power needs, in the global energy picture, are still negligible. To realize the technology’s backers’ visions, the electrical consumption would have to keep growing at this breakneck pace. At a time when climate change requires that energy demand be bent downward, bitcoin miners sucking up city-size supplies of cheap and carbon-free hydroelectricity is a massive problem. And in China, where most mining is done with subsidized electricity produced in coal-fired power plants, it’s an even bigger problem.

This externality alone could wipe out a range of the benefits that bitcoin advocates imagine could result from the use of cryptocurrencies. Let’s stipulate that blockchains are useful and interesting. But will they be worth the energy it takes to do all that computation?