As I was reading a new paper published in Quaternary Research about how small changes the Sun's activity may effect weather and climate, a thought hit me. Before I tell about my thought, let me say that scientists in this area will probably laugh and say that this is basic knowledge.
Let us say the Sun changes 1% in total radiance, I would assume one should assume a forcing in temperature range of 1% of the absolute global mean temperature. Let's say the global mean temperature is 15°C or 273+15=288°K. Thus, 1% of 288°K ~ 2.9°C. Long term changes, has to be an integral dependent on the thermal time constant of particular the oceans, less than 2.9°C would give an idea of the negative feed back gain.
That's it, just a thought from a novice within this area.
Update July 31st 2013 - The 0°C to °K value corrected, sorry.