From a comment in a different thread:
What will be scarce in the future.
As I've noted in the past...I consider Julian Simon's work to be among the most revolutionary ever done. His fundamental thesis is:
Non-renewable resources are NEVER scarce for long.
If you take this seriously...you run into a crazy position (along with Simon), that I agree with: the only shortage that is even sane to talk about is a shortage in innovation.
Shortages in innovation come from 2 places:
1. Insufficiently many minds (underpopulation)
2. Crappy regulatory structures.
Now...if you stack Drexler's conservative hypothesis (When a desktop computer has somewhat more than the computing power of a human brain, it will be roughly as able to innovate as a human brain, regardless of whether we call it intelligence)... that leaves running out of resources subject to exactly one constraint:
If you further include Mancur Olsen...the problem is that existing interest groups capture the regulatory apparatus in order to solidify their own relative standing, thus slowly killing innovation. I'm personally creeping towards the conclusion that Cowen's great stagnation is (a) true, and (b) the necessary result of ever increasing numbers of regulations put out by government agencies...which has happened under every regime ever built (Including recently Singapore). The problem, unsurprisingly, is then:
Too Much Government.
If we can restrain it...we don't have resource constraints. If we can't, we do.