Greenhouse Gases Are GOOD. Too much GH is BAD

Last Fall, months after starting my pro-nuclear-energy blog, the true value of greenhouse gases finally became clear. Are other people aware of the thought that, without this natural phenomena, humanity and most other organic life, might not even exist? Per wikipedia site  (http://www.en.wikipedia.org/wiki/Greenhouse_effect), the partial blanketing effect of water vapor and other gases like CO2, keeps the Earth’s atmosphere near +15-degrees C (15C above freezing; water freezes at 273C above absolute zero), rather than -15C (below freezing) that it would otherwise be. (59F, not 5F). Without this blanketing, Earth’s land surface would probably be frozen solid. Other than marine life, organic creatures might be impossible.  

I’m guessing that water vapor might have kept the Earth’s atmosphere above freezing for hundreds of millions of years. Then, as organic life spread over the land, the CO2 cycle added more GH to bring us to about +15C; which we would like to stay at. (Note how tiny this number is, relative to water’s freezing point of 273C above absolute zero.) The CO2 cycle has been a zero-sum game since long in the past when an equilibrium was reached. (Plants grow by absorbing C (carbon) from CO2, giving off O (oxygen), then reverse to produce CO2 when they die and decay, or are burned). Our problem right now, is that all of the fossil fuels that have been burned during the industrial era have raised Earth’s CO2 level, and the temperature, several degrees C, above the natural equilibrium. Just a very few more degrees could turn out to be catastrophic.   

PS: Destruction of forests adds (about 20%) to the CO2 excess; new growth is not fast enough to be an adequate sink.