I've studied that, it's easy if you bothered to look it up. It is to do with natural perturbations in the orbit of the earth around the sun (Milankovitch cycles) which caused slow and small variations in temperature which in turn caused the releasing or absorbing of CO2 by the oceans into the atmosphere which caused feedback loops which caused the temperature to continue changing. The amount of ice on the surface of the earth was another feedback loop - as the earth got colder it added more ice and reflected more sunlight back into space causing temperatures to keep dropping, then more CO2 being absorbed by the oceans then temperatures dropping further etc etc (a feedback loop). It was a change in Milankovitch cycles that would reverse the trend, trends which happened over scales of 100,000 years or so. What we are seeing now is happening over decades, much much faster than what has happened in the past, because there has been a 40% increase in CO2 levels and humans are the cause.
Rather than rabbiting on about this, why not go back to school and study science or at least try looking it up on the web?
