If you could implement a perfect global tax system, a high tax on energy used specifically for mining would be a good solution. Proof of work is designed to for

If you could implement a perfect global tax system, a high tax on energy used specifically for mining would be a good solution. Proof of work is designed to force miners to spend a given amount per bitcoin mined, and it doesn't matter whether that amount is spent on energy or taxes, so the tax would not actually cause any economic cost to miners. Unfortunately, such a scheme would highly incentivize cheaters, or countries opting out of the tax collection.