[sesqu]

  World GDP has grown at an average annual rate of 3.5% over the last 100 years.

That's not actually very relevant. According to DeLong[1], the rate of growth has been anything but constant over the last 100 years, nor has it always been positive. You may well expect the industrial revolution to carry us forward for another 150 years, but I'm not sure if I do.

[1] http://img641.imageshack.us/img641/1946/gwp.png

edit: corrected the 2000-2011 segment for inflation with CPI data (not int$).