The sooner we can move away from fossil fuels and on to renewables, the less there will be an argument against cryptocurrency mining on coins which use proof of work can be considered partially wasteful. The irony is, that a lot of the precious and rare metals used to create things like solar panels can be very damaging to extract from the environment, but hopefully they're used in a way that is more useful than burning up single use fuels. We're all sharing this planet which is slowly heating up, so should all be thinking about ways to save energy, because there have already been vast changes in the last few decades and we might even see the ice caps melting in the near future.