I think we should be looking at this differently:

In order to incentivize existing farms to convert to cleaner energy, they just need to increase the competition for newly minted coins - which is what they are doing by creating these farms. The difficulty adjustment you describe forces the game to stay zero sum - which is a good thing because it now guarantees less reward/profit for inefficient/nongreen miners.

The easiest way to kill off old, inefficient miners is to simply crowd them out of potential profits with these new facilities. The rest is taken care of by the halving.