So we are all agreed? Greenhouse gas molecules absorb photons and the resulting kinetic energy from bending and stretching bonds heats the atmosphere. More molecules absord more photons and the atmosphere warms. Warmer molecules emit more photons in the IR. There is no ‘notch’ in the emission spectrum for God’s sake. Otherwise we would see it measured directly rather rather than brightness temperature calculated.
Can we move on from the basics? This is an intersting site – http://www.whoi.edu/main/topic/abrupt-climate-change – climate change when it happens is abrupt and non-linear.