Glacial changes in the Earths history can be traced back via ice cores, and can be deduced from a number of factors. The Earths eccentricity is the first of these factors in changing on a time-scale of around 100,000 years. Eccentricity is simply the changing of the Earths orbit from being more like more elliptical, to being less elliptical with time. The second of these is changes in the axial tilt from 21.5 to 24.5 degrees. The third factor, is the Earths precession or wobble as it orbits the sun. This changes the North Star from being Polaris, to Vega.
These things put together are called the Milankovitch cycles.
This illustrates the Earths precession some fair justice:
(http://www.geography.hunter.cuny.edu/tbw/wc.notes/14.climate.change/axis.precession.jpg)
It is these small changes that change the distribution of sunlight radiation on the Earth and radically alters the seasons, climate, and brings into and out of Ice-ages an Holocene.
(http://www.southwestclimatechange.org/files/cc/figures/milankovitch.jpg)
We can also see looking back, that green house gases (GHC) both follow and drive climate. The reasoning is simple: as the climate warms, more GHG's are released into the atmosphere, further heating the earth, and this feed-back continues until the Earth reaches balance again. This is why the argument that GHG lag temperature is a non-sequitur; GHG's act as a feedback that amplifies temps.
(http://ossfoundation.us/projects/environment/global-warming/myths/images/natural-cycle/Forcing-Temp_1.9wm2.png)
See why climatologists and atmospheric physicists take climate change seriously? Again, the science is pretty settled.