John, off topic I know, but after rereading your link to 1816, I followed the link to a list of major worldwide eruptions. They happen with surprising frequency.  If I were a betting man, I think the odds of another year without a summer are better than the odds of some of the bearish arguements.
  Wouldn't want to be short grains if one of these events happens, no one has any insider info on when it will happen either, Could be locked limit up for weeks on end, unable to get out.  
http://en.wikipedia.org/wiki/Timetable_of_major_worldwide_volcanic_eruptions

This just in the last 160 years:




I occasionally refer to this image, puts our current situation into perspective: