I watched an interesting show on the Discovery channel called "Snowball Earth" The theory was that at one time in earth's history that virtually the whole planet froze over. Whether it actually did or not is debatable, with facts helping to either prove or disprove the theory, but some interesting "facts" came out of the show.
That the main contributer to ice ages is the orbit of the earth around the sun and the times that we are further away from the sun co-incide with the ice ages. (makes sense, less heat the colder we are)
That the sun is getting warmer. If I remember correctly it was something like the sun is 6% warmer than it was 640,000 years ago.
The role of carbon dioxide in the temperature of the earth. More carbon dioxide in the atmosphere the warmer it gets and vice versa. Mother nature has a normal balance for this, as the more carbon dioxide in the air the more the plants grow and the more plants there are, the more they take the carbon dioxide out of the air.
At one time our atmosphere had a lot more methane in it, but the release of oxygen from the ice changed that.
It is the amount of oxygen in the air (the pressure of the oxygen) that allowed for multi-cell organisms to grow.
I don't know the term for it, but it also talked about how events that cause the earth to heat or cool, cause other events to occur that accelerate that trend. Example as the ice melts, it creates more areas of darker water which absorbs more heat, which makes things warmer which melts more ice and the cycle continues. They showed an example of a white SUV beside a dark SUV in the sunlight and the white one had a surface temperature of 120 F and the dark one I believe was 144 F.
I'm not a tree hugger, but it help me understand a little better the whole global warming thing. The huge changes in the earth's temperature will be regulated by things greater than ourselves such as the orbit of the earth, but it is simple physics that if we add more carbon dioxide to the atmosphere and at the same time cut down the trees that help eliminate it, that there will be more carbon dioxide in the atmosphere and the temperature will increase.