Can we agree on the following...?
1. We are affecting our environment through various forms of pollution.
2. We have become dependent on, and are rapidly using up, finite resources such as fossil fuels.
3. In the long run, we'd probably be better off doing less of both.
To me, that's the important stuff. Whether Item 1 includes global warming or just other, more easily provable, things (case in point: the lovely central NJ groundwater, or the huge ozone hole now affecting millions of people in the Southern Hemisphere) is beside the point. Most of the things that they say contribute to global warming (massive burning of fossil fuels, slashing and burning acres and acres of rainforest to raise massive herds of cattle, etc) have other negative effects.
Why waste all this time and energy debating whether or not the smog that we're continually releasing into the atmosphere is affecting our climate, when I think most of us can agree that we'd rather not be breathing it?
