The one thing we must consider is that the total mass of the earth and its atmosphere can neither gain nor lose in its magnitude with the posssible exception of aggregate matter from meteorite strikes, any wobbles in our orbit are imbalances in the manner that a unbalanced wheel on your car might set up an oscillation and thus become noticeable.
The big problem I have with global warming is that it is universally advertised as being deleterious over the long haul; but for whom?
There are a wide variety of well known, regular periodic wobbles in the orbit of the earth known as the Milankovitch cycles; the axis of the earth wobbles up and down, wobbles around in a circle, and the shape of the orbit changes slightly; this ends up changing the amount of solar heating the Northern Hemisphere gets.
http://en.wikipedia.org/wiki/Milankovitch_cycles
It's clear the combination of the above is a major cause of glacial periods and interglacials, but the fit isn't perfect and the whole issue is pretty complex.
Based on them it should still be quite a while before the next Ice Age, according to a lot of people.