Why do my bit now?

Here is a video arguing about why we have to bring in policies changes to thwart global climate change -
http://green.yahoo.com/blog/ecogeek/244/high-school-teacher-spreads-the-word-on-climate-change.html

One interesting argument is - Why did we build the atom bomb just on the fear that Hitler might build one! If one man's fear resulted in building the atom bomb, why can't we tune in and realize what the hundreds of environmentalists are saying?