I hold 2 degrees in Biology (BS in Ecological Sciences, and a MS in Genetics). I had 2 professors in back to back classes that both had air-tight cases for their theories... First professor stated Global Warming was here and we were making it happen at an alarming rate. The second professor stated Global Cooling was here and we were directly responsible. Who was right? Oddly enough, one of my genetics professors partnered with a Archaelogical professor to perform scans of material from tens of thousands of years ago who showed proof that the earth cycles through warming and cooling periods, some of which were fairly rapid (i.e. over 50-100 years) some of which took longer. While I agree that humans are contributing to the global warming problem, I don't agree that immediately ceasing our current activities will change the climate. Climactic change is gradual and cumulative. If you compare the amount of time humans have been on the earth to the amount of time the earth has been around, you could think about the history of the earth spanning a time table the height of the 20 story Building. The history of humans on that same time table would be the equivalent of the thickness of a single piece of paper on top of that building.

And if you think humans cannot effect an environmental change, think of this... If we exterminated all of the bees in the world, all life on the planet would die within a year.

I think we can more directly affect climactic change by advancing new techologies for cleaner buring combustion and finding ways to restore the balance (instead of listening to the guy who invented the Internet).