Atmospheric Gases

H2O = 4% of atmosphere
CO2 = .04% of atmosphere
man-made CO2 = <1% of CO2

CO2 is a rare trace gas that is essential to our biosphere.  Why would we want to limit it?

CO2 hit 500+ PPM in 1800s, according to Slocum’s unedited data.
http://junkscience.com/2013/05/13/warmist-waterloo-did-the-atmosphere-hit-500-ppm-co2-in-the-1800s/

Mann makes no predictions?  A scientist put forward a theory with no predictions?  How on earth can that theory be validated without predictions?