Global warming alarmists would have us believe that a doubling of atmospheric carbon dioxide from current levels around 350 PPM (parts per million) would be the end of life of life on Earth as we know it.  I'd like to take a look at this claim in the light of what one could call "planetary common sense".

Our atmosphere is roughly 79% nitrogen and 21% oxygen, plus trace gasses.  If an alien race were to look at this composition, it would be apparent that life exists, because that much free oxygen could not exist in the atmosphere unless some process outside of the normal entropic chemical reactions were occurring.  There are just too many things that like to bind with oxygen, and without life the presence of free oxygen in the atmosphere would be minimal.

Science tells us that the road to life on earth as we know it started with the evolution of photosynthesis in primitive blue-green algae, which ultimately transformed our atmosphere by converting carbon dioxide, water, and sunlight into simple sugars and oxygen.  The algae got the chemical energy and building materials it needed, and our atmosphere got oxygenated.

Now here's the rub - to generate the current levels of oxygen, there must have been at least 21% carbon dioxide in our atmosphere prior to the evolution of photosynthesis.  It was likely much higher, when one considers that much of the carbon in the incredible biomass of our planet came from the sequestration of carbon from our atmosphere.

To put this in terms of the roughly 350 PPM of carbon dioxide in our atmosphere today, at one time there was at least 210,000 PPM of carbon dioxide in our atmosphere!

How could life have ever have come to be if this planet was such a greenhouse?