Earlier quoted context omitted.
The miners must set a rough minimum fee though. If energy costs rise enough at some point the miners will need to slow/shut down unless the sum value of the fees (in whatever currency is used to pay for the energy) rise above some threshold.
They're not setting a minimum fee, they're either mining or not mining based on profitability. There is never any financial reason to mine blocks that have empty space if there are fee-paying transactions available to put in that space.
If costs go up (eg energy becomes scarce) the minimum fee also need to rise. Each "unit" of economic activity using the currency will be more expensive when energy is scarce than when it is abundant. This is a natural feedback loop.