Here it states:
It’s a common misconception that energy usage scales up with the number of bitcoin transactions and that if Bitcoin ever became widely adopted for payments, then the energy usage would be enough to boil the oceans.
but then again:
the effort spent securing the network scales automatically with the value of the transaction data on the blockchain—not the number of transactions. So the more value there is riding on the Bitcoin network (because individuals value it more as reflected in the price), the more resources will be devoted to its security.
If I understand this correctly, this would directly translate into:
More users and demand leads into greater energy usage due to Bitcoin's price increasing.
There have been some estimates of the network using around 170 TWh per year recently (some may have lower estimates).
Apparently there are currently approx. 83 million "wallet users" (link), whatever that means – they cannot know how many wallets would be owned by a single user. So currently roughly only around 1 % of the world population are these "wallet users" (actual number of people could be much less though).
If we were to just naively extrapolate linearly Bitcoin's future energy usage for the entire population the number would be quite enormous. However, the value in the blockchain does not increase linearly during adoption, but instead the price growth is exponential.
Given these numbers, how would you estimate Bitcoin's energy usage in the ultimate case of full adoption?