Bitcoin is an energy currency.
If anything, bitcoin mining is a disincentive in making a more energy efficient green economy: instead of reducing waste and reducing power production as needed, we now have a way to turn excess power production into money directly. While a carbon tax could have shut down a coal plant, now the coal plant could instead get a bitcoin mining rig and power that, as long as the carbon tax is lower than the (extremely volatile) value of bitcoin.
To avoid the most apocalyptic effects of global warming, we have to close down most fossil-fuel based energy generation today, literally. Bitcoin is actively working against that by driving up the price of electricity to fuel a speculative bubble.
Not a currency, but a digital asset that wastes enormous amounts of energy.
It's in the top 20 or so of world currencies, and it's still in its infancy (thus volatility etc).
My question, then, is how do we go about drowning Baby Bitcoin in the metaphorical bathtub?
What do I do with my profits from mining bitcoin? Send my kids to college, buy groceries, remodel my bathroom, etc. It's an entire ecosystem, speculatively mining bitcoin by consuming electricity is just as evil as driving 1.5hrs to work because you're too lazy to find something near your house for example. People expend trillions of dollars in energy "mining" fiat.
Sure, the monetary value of that energy may be getting stored, but we can't buy lower temperatures with money, unfortunately.
When you store energy by pumping water for example, you can later let that water flow to get back the energy itself (with some inevitable waste, of course). When you're converting energy to bitcoin and later require energy again, you have to use the bitcoin to buy more energy (either from the market or by building a new power plant or something), you can't just physically convert the bitcoin back to energy.