I keep hearing this notion repeated, but I've never seen a citation.

Do you have any evidence that:

a) Most bitcoin in China is mined using hydroelectric power.

b) That the generation capacity in question is "excess" (i.e. it would not have been put to productive use except for bitcoin mining)

It's also worth noting that damming rivers for hydroelectric power is enormously damaging to the surrounding ecosystem, even if they aren't carbon-emitting: https://en.wikipedia.org/wiki/Environmental_impact_of_reserv...

Fully agree. Following suggest coal is still the main source of energy for Chinese miners.

https://qz.com/1055126/photos-china-has-one-of-worlds-larges...

https://www.bloomberg.com/news/articles/2017-12-15/turning-c...