To add to this, people are failing to grasp that AGW is about how humans are applying a small modulation to an existing system, and there are small changes, but they are very significant for life on earth. With CO2 at all, the planet would be some 50 degrees cooler, I believe. Raising it by 3 or 4 degrees, therefore, is not a big deal in terms of the numbers. But it is a big deal when it causes sea levels to rise and some land to be inundated. Again, it's not a lot of land. Most land will be fine. But we have a lot of cities on the coasts. That's a big deal for humans. When rising CO2 increases acidity levels in the ocean, it still may not be by much. But it's a lot for the life that lives there, that starts to die off when it can't handle the change in water chemistry.
What we are talking about is life's sensitivity to change, not about gigantic changes to the atmosphere (which we really aren't making). Life can handle change, but over larger time periods. When there are significant changes in a short time period, a lot of life dies off. Of course, in time, it will recover, as it did 65 million years ago, or during other extinction events. It's bad news for humans, though, because we depend on the ecosystem as it is. We can mitigate with technology or general inventiveness, but it will be a very big blow to our current civilization. That's why people should care. Not because the planet will explode (it won't). Not because one weird species of frog in outer Mongolia will go extinct (why should anyone care about that anyway?). Not because temperatures will go up by a billion degrees (they won't). It's because the small changes made to a climate that has been fairly stable for civilized human history have big effects for life and human life, which is sensitive to small changes. What good is oil and profit if we can't eat, can't live where we used to? That's the trade-off.