The more carbon dioxide we exhale or produce, the more the process of photosynthesis converts it back into oxygen and carbon. Ever wonder why the oxygen levels never seem to decline with the more and more hydrocarbon fuels we consume? As long as we have green things, sunshine and water, photosynthesis will strike a balance. That is all the science in a nutshell, not just the half in an agenda.
Woody
The flip side is that we don't have nearly the amount of green stuff that we used to. And while we may have the same amount of oxygen, we have more carbon dioxide and that is what they point to as the issue. The atmosphere, like the Earth's crust is a system of variables that will find a balance. When you change some of those variables, the system will find a new balance.
I'm not an environmentalist, it just seems to me that all things require a happy median and I do worry that we will unbalance the system and it may bite us where the sun don't shine. I also don't trust excessive collections of power whether that be in big government or big energy. Like any good individualist, I like to limit the control others have on my life which is why I am so very in favor of increasing competition in the energy industry by adding other prime movers (wind, solar, nuclear, etc etc).