Bitcoin is not directly responsible for the carbon emissions the miners produce. Those who own farms can always opt to hash with cleaner and greener energy, but if they are getting good deals from their local power company then so be it (I believe it's way less than the average household rate that power companies charge regularly, but that differs depending on where you're at). That's why you see some farms migrate to Iceland, the provinces of China and other areas where renewables are readily available and cheap to harness, much cheaper than having a marked-down contract from your local power company.
The problem is that energy is generated by burning carbon. The problem is not how the energy is used. If you want to stop carbon emission, or at least slow it down, stop burning carbon.
Easier said than done, especially if the governments and power companies are conniving with each other the continuous use of fossil fuels rather than allowing nuclear and other cleaner and greener types of energy to flourish.