You need to think of everything humans do. CO2 is a big thing, but it's far from the only thing worth considering with "the environment". Big points to read about:
1. Water: pollution here from chemicals used in every single industry plus the private sector leak into the planet's water. Changes EVERYTHING on the planet. Coral bleaches, fish die, animals and people get cancer or have weird gender effects... If you think drinking toxic stuff is great, you can ignore this. But it's huge, and scary.
2. Consumption of goods (everything you buy): Manufacturing is dirty. Transport is dirty and expensive (carbonwise as well as time and materials). Think of how much stuff you throw out in a week, a year. A heck of a lot of that goes back into the water. You are pumped up with commercials to want more. Limited resources, people! If populations keep expanding, we won't have enough for even food/shelter for everyone, and this leads to war usually. No one wants to die after all.
3. Biodiversity: If we only think of humans, what happens to everything else? Take a look at Wikipedia. http://en.wikipedia.org/wiki/Biodiversity Now think about killing a lot of animals because you wanted to have three computers and two cars and an Ipad and a biiiigggg house and lots of other stuff. And then you have to hope to goodness other species step in and fill the gaps left in the ecosystem well enough. We're missing a lot of bees, and crops are suffering for it, and food prices are rising. This effects us quite directly.
And while we're starting to see the effects of a human-centric viewpoint, it's our kids and grandkids who have the burden of dealing with what we leave behind. So, better to read up and be careful. CO2 is masking the whole of the problem and it's letting people bicker over small points. Makes me a little angry.