Look whats happening in France about fuel taxes, something similar will happen when cryptocurrencies adoption comes to life and if they want to raise taxes above moderate heights.
That's inevitable. I say that because in every growing industry or market alike, government entities would try to capitalize on it by either imposing taxes on it to add revenue, if not, try to control it in some way whether indirect or direct in order to have some leverage or advantage to it for future use. Although the cryptocurrency market is an up and down market, it can still yield good capital and profit if you see the bigger picture. Therefore, by imposing taxes, a government gets to control how the market goes in their localities.
But you can't assure that the government will use the funds collected from crypto taxes in addressing the pollution issues. They might use it in some other major problems that they think need immediate attention. And you are hoping that the government will not be corrupt on its own.