First thing's first: look out the window. Note how the sky is clearly visible, since you're not seeing it through a thick layer of ice? That's because the Permian ice shell around the planet melted. The planet warmed up. It's pretty obvious, putting two and two together, that global warming exists. Now, the Greenhouse Effect? Anthropogenic global warming? That's a different kettle of fish. The planet is warming up, and all our predictive models say that this is (at least in part) our doing, but there's almost no proven causal link. Of course, by the time one was established, we'd all be hopelessly screwed, so waiting for one before taking action makes no sense.
That said, look at the action that's been taken: we have people, even in this thread, talking about "carbon footprints". Carbon is not a greenhouse gas; carbon isn't a gas at all. CO2 is, yes; but 1. it's far from the only one, 2. it's far from the most potent one, 3. you produce it by breathing, making it essentially environmentalist original sin, and 4. industrial and governmental sources produce a whole lot more than individual people do (though that may not be the case in every country). Remember, if those frozen methane hydrates in the ocean start melting, the resultant greenhouse hit will make all the CO2 humanity's ever produced look minor in comparison.
The key thing to bear in mind is that even in the worst case scenario, this isn't a world-destroying problem, like CFCs erasing the ozone layer was. The damage will be catastrophic, yes; but not as bad as the P-T extinction, and probably not even as bad the K-T. As part of the species that survived Toba, I'm not real worried for us. I'm not happy about the prospect of civilization being destroyed, hideous suffering and the bulk of the species dying in agony (though living in the Yellowstone blast zone, I get to look forward to a much more rapid and cinematic death), but 1. I'll be dead, and 2. the descendants of those who rebuild will no doubt get some kickass video games out of it.
