If Bitcoin disappeared tomorrow, it would give a small reduction in energy use, but at best it buys you 6 months extra to decarbonize electricity production.
Also what does btc and crypto replace? The carbon footprint of traditional finance, banking and the military actions to preserve it are massive polluters. Even at its infancy, pow crypto is already a good direction to improve sustainability.
I think crypto has a lot of socially useful potential, beyond mere speculative gambling and Austrian-school value storage, but that's in addition to the centuries of momentum in our real-world political economy; crypto-currencies are unlikely to replace that entirely, anymore than the internet replaced the New York Times.
6 months can be a tipping point happening or not.
Additionally, each produced ton of green house gases is contributing to climate change right now
The more electricity to decarbonize the more difficult.