First of all, I and the majority of scientists believe that man-made global warming is happening. So it seems that we should take steps to curb emissions, recycle, reuse and take care of natural environments. But for those that don't believe it is happening, I give one simple reason why you should do something about it anyway. If you consider the earth's atmosphere as the air in a large room in which you were situated, would you rather have more artficial pollutants in the air to breathe in or less? Which is more natural? Which will have less of an impact on the environment? That's all the naysayers on global warming need to think about. Less bad stuff is good. Our atmosphere is not infinite and it can only handle so much.
So, try to live efficiently, drive efficiently, use less, waste less.
On a related note, see this ironic article. Canada wants to build an oil pipeline, but because of global warming (which can be partially attributed to emissions from oil product usage), the permafrost, (used to always be frozen ground), is now melting. This would make a pipeline a dangerous proposition because the ground beneath it could not be relied upon for support. Perhaps nature is telling us to use less oil.