I am a geologist, and anyone familiar with geologic history can tell you a (true) tale of wild climatic variations that can be observed in the rock record. A russian scientist named Milankovitch made the interesting oribital cycle observations you mentioned in papers published in the early 20th century. He was dismissed as a kook until the evidence began to confirm many of his theories about orbital influences on climatic variation. It is by no means the only influence, and some aspects of his theory have been refuted, but the broad idea he promoted has some merit. Google his name for a whole boatload of commentary. Here is a representative and reputable link:
http://aa.usno.navy.mil/faq/docs/seasons_orbit.html
It is very hard to get real facts about this nowadays without a lot of political cant interwoven in the science. No one ever got grant money for research by stating "There really is no problem to worry about, but I'd like to research it anyway".