While Bitcoin mining consumes a huge amount of electricity, does it necessarily translate into increased carbon emission? In an analytical model featuring endogenous renewable energy adoption decisions, we show that with appropriate electricity price policies, the high electricity demand from Bitcoin mining may actually subsidize the capacity building of renewable energy plants and thus lower total carbon emission. A key intuition is that unlike other electricity uses, Bitcoin mining intensity can be elastically dialed up or down without disrupting operations, and thus can replace fuel-based electricity generation as an effective shock absorber for the volatile supply of renewable electricity generation. We characterize conditions when this carbon emission reduction effect stands.