Even without science I can tell you that if you introduce something(a foriegn substance) to a object it will change it. Good example. The human body, we know that if you smoke cigarettes(spelling, sorry), it will cause cancer if you keep doing it.
End of quote
The problem is your analogy. The human body is a part of nature, but not all of it. SO yes, there are parts of nature that are foreign.
The earth is all of nature. So far, except for a few moon rocks, man has not introduced anything into this planet that was not already there in one form or another. And nature has taken care of it - just not on a timetable acceptable to man.
Man is not accounting for a majority (not even close) of CO2. The earth has done that herself.
The problem with all this religion about global warming and "destroying" the planet is the hysterics. What we are doing (possibly) is killing ourselves, which we do have the capability to do. But the dishonest want us to beleive we are killing the earth - which we cannot. And some are even so insane as to say that man is the cancer on the planet. And that the only solution is our erradication. I am sure in time, that will happen. But rending clothes and committing hari kiri to demonstrate your point may be good for your soul, but does nothing for the real issue, obfuscated as it is.