PoW is different because it's energy use for its own sake.
If carbon taxes go up, some things will no longer be worth spending energy on, but crypto mining is just competitive, so the value of mining will go up with the cost of energy and keep using as much energy as ever. The only thing that can stop it is reducing demand for the coins, which the government is not even trying to do yet.
> but crypto mining is just competitive, so the value of mining will go up with the cost of energy and keep using as much energy as ever.
That is not true. If the cost of energy increases, mining / hash rates will decrease. Miners are competing, and the limit to the price they will pay for electricity is the value of the cryptocurrency they are earning for the activity.
If carbon taxes go up, miners will be incentivized to pursue low/no-carbon alternative energy sources, thereby accelerating the shift to cleaner energy. Mining can either be viewed as creating a profit incentive where none existed before, or at least enhancing the profit incentive even further. Clean energy needs more profit incentives to really scale adoption.
I am all for carbon taxes, to shape the market towards cleaner energy. And I do think it will successfully push miners even faster towards adoption of other energy sources.
If carbon taxes go up, some things will no longer be worth spending energy on, but crypto mining is just competitive, so the value of mining will go up with the cost of energy and keep using as much energy as ever. The only thing that can stop it is reducing demand for the coins, which the government is not even trying to do yet.