Nature Climate tweeted:
RT @climatereality: Last time CO2 level hit #400ppm, the #Arctic was 8°C warmer ow.ly/lcXLw
— NatureClimate (@NatureClimate) May 21, 2013
So if it was so much warmer at 400 ppm CO2 then, why is it so much cooler at 400 ppm CO2 now?
Because CO2 is a small player in temperatures and climate and because warming outgases CO2 from water? Just guessing.