I think instinctively, adopters of Bitcoin will immediately turn to raising Bitcoins supply cap (probably by 2x) to solve this issue.
As already said by others, this will never happen.
If you want a coin with 2x supply, that's no longer bitcoin. That's would be an altcoin (which can be forked from bitcoin)
One solution to this problem will be to make the amount of power used to mine blocks significantly lower as that will incentivize miners to mine blocks with lowers transaction fees.
Again, we would need a fork.
The forked coin will be no longer bitcoin. It will be a very insecure altcoin.
To decrease the energy consumption, we should reduce the difficulty. In the case the difficulty is reduced much, it would be easy to perform a 51% attack.