It was discovered in 1928 that the Earth’s rotation was irregular. How much global warming induced glacier melt was experienced back then?
We’re also supposedly losing the Moon. It’s slowly drifting away from the Earth at the rate of about 2 inches per year. Without the Moon, the Earth would begin to wobble uncontrollably. Seasons would be chaotic. The Moon keeps our 23-1/2 degree rotational axis stable.
There are 3 separate orbital/rotational deviations. The shape of Earth's slightly elliptical orbit changes periodically. The tilt of the rotational axis changes periodically as well (it's currently at 23.5 degrees). Next, the direction that the rotational axis points...in relation to the Sun...changes periodically.
Great illustrations and deeper explanations here:
http://earthobservatory.nasa.gov/Features/Milankovitch/milankovitch_2.php