I saw part of that movie The Inconvenient Truth during science class yesterday. It was wonderfully made, and kind of scary because you know this stuff is really happening as we speak.

As to your question Wombat, the reason we've had many Ice Ages and stuff is because of the amount of carbon dioxide in the air (or maybe it was carbon monoxide). Anywho, the amount of CO2 in the air coincides with the temperatures. Over to past 4.5billion years, things have been pretty steady. Yes, the CO2 levels have dropped before, causing an Ice Age, but they have always risen back to normal. However, in recent years, CO2 levels have skyrocketed. We aren't sure how bad this will affect the temperatures, but it most certainly will.

I can't explain all that I saw in the movie, so I highly suggest just going to rent it.