I saw the movie (documentary) An Inconvenient Truth yesterday. Very powerful. I encourage you (anyone) to go see it. A powerful presentation on the very real problem of global warming. It's an important issue. What kind of world do we want to live in in our futures and our children's futures? The climate changes due to green house gasses causing global warming is real, it's happening now. If we don't start doing things differently, it's going to get much worse.
It's not just a matter of temperatures a few degrees warmer. It's about floods, droughts, hurricanes. The disaster caused by hurricane Katrina may very well be our doing, not just by us choosing to build a city in such a low lying area, and trying to control the Mississippi and all that (though that too), but because, with green house gas emissions, we have raised world temperatures, including ocean temperatures, and warmer oceans makes for stronger hurricanes.
Go see the movie. It's well made, engaging, and it's a very important topic.