If you can't explain the 'pause', you can't explain the cause...
William Happer recently appeared on CNBC's Squawkbox show, discussing the 400ppm story.
When the earth had 4000 ppm, (450 million years ago), the sun was much dimmer. 4000 ppm NOW would be a total disaster. The previous spike in CO2 around 650 million years ago pushed the temperature of the earth by 50c, up from arctic temperatures near the equator, to higher than modern temperatures world wide. The world has warmed since 1998. 2005 was warmer, as was this year 2013. Agriculture production is going down due to greater variation in climate. Corn production failed due to heat, pushing up price of corn by 40% world wide.