To compare with Sterling and Lebkowsky. Charlie is trying to look at possible scenarios for 2032 and 2092. What strikes me most about the commentators is that there's a common failing of looking at a single factor and trying to extrapolate that out (like say Oil or Education) when it's just one factor in a holistic system. It's extremely hard to predict anything without a full scale economic model. The second failing is to view the future as just like the immediate past with a small amount of technological progress and a small linear increase in everything. Yet again, it's time to go back and look at The Limits To Growth and to try and understand the real meaning of exponential growth.
75 Trinity Rd
If you look at gross world modelling of such things as changes in population, energy use, food production, industrial output, then 20 year predictions seem entirely feasible to me within some error ranges. A sustained boom or a sustained recession shouldn't affect the curves that much but just shift them 10 years either way.
I quite agree though that 2092 is more like pure speculation. Perhaps all you can say is that a complete game changer is fairly unlikely in 20 years and fairly likely in 80. But again, how much of the world in 1992 was predictable from 1912? Global air travel?
http://www.antipope.org/charlie/blog-static/2012/01/world-building-302-psychology.html#more