What is a likely solution to Bitcoin's energy consumption problem? If the price of Bitcoin continues to climb, the total energy consumption of the system will increase proportionally at least until 2020 when block reward halves. It is not unlikely that at this point the price of Bitcoin will have increased so much that energy consumption will be unsustainable in a way that Bitcoin will be opposed by a large proportion of global society (we are still below 1% of total electricity consumption but a 10-fold price increase could change that quickly).

I see the same options that are laid out in this article:


Bitcoin will be abandoned and people just use something else
the protocol is changed to reduce the block reward earlier than 2020
the protocol is changed to exchange Proof-of-Work for something else (maybe Delegated Proof-of-Stake?)


since 2 and 3 will almost certainly result in a fork, they are related to 1. I feel that a solution will have to be found, I'm just wondering if I missed another option and which of the options is most likely.
I feel that a solution will have to be found


I'm not sure I agree there is a 'problem' that needs to be explicitly fixed. The article you linked explains the relationship between price and electricity usage, now remember that price is a measure of the demand (since the supply is fixed and known). 

So the market acts as a naturally regulating force: as people pay more and more to buy and use bitcoin, the network's power consumption will increase (and vice versa). So to say "bitcoin uses too much energy!" is to say "bitcoin is worth less than the current market value!". The article linked supports this point, but you kind of have to 'read between the lines' to realize it is true.

Consider gold mining: if the price of gold were to rise, then it would become profitable to start mining gold in places where a more expensive  processes will be needed to extract the gold from the earth. Is it a problem that companies will spend a lot of energy to get this extra supply that is now worth while? 

Interestingly, consider what happens if the demand for bitcoin continues to increase, to the point that the network is in direct competition with all other use cases for power. In that case, for the btc price to increase, electricity prices would have to be increased, effectively spreading the cost of mining across all of the world's energy usage (because if the demand for bitcoin did not exist, everyone would be paying less to power their home appliances, etc). 

I think it is easy to say "this is a problem!!", but the less obvious realization is "bitcoin is using this much energy because the market considers it useful enough to be worth the cost"


  I'm just wondering if I missed another option and which of the options is most likely.


I don't think any of the three options you listed are likely to happen. 

Another 'option' to consider is this: once mining chips become commodity (more easily and readily available from multiple suppliers), I think the nature of the mining competition will change. If everyone has access to good ASIC chips, then there will be immense competition to develop and utilize the cheapest sources of power available. What if bitcoin miners must help fund the development of ultra-efficient solar panels in order to maintain a competitive advantage? This is how ASIC miners were developed, why can't the same happen for another variable in the mining industry?

If this occurs, rather than the energy consumption of the network being a problem, it becomes an incentive for finding a solution to the larger issue of 'needing to develop green sources of power'.