Here is an iinteresting site referenced by deadreckoningfubar.blogspot.

http://www.iscanadaready.com/facts.htm

Take a look at the temperature of the world for the last 400,000 years. It appears we are reaching the point where the temperature takes a steep decline. Maybe we need some more greenhouse gas effect to keep from descending into another ice age. The chart shows the last 4 ice ages. I've read before, as I recall in the book "The Little Ice Age," there have been 21 ice ages in all.