...the most important debate is global warming research today is the same as it was 20 years ago: How will clouds (and to a lesser extent other elements in the climate system) respond to warming, thereby enhancing or reducing the warming? These indirect changes that further influence temperature are called feedbacks, and they determine whether manmade global warming will be catastrophic, or just lost in the noise of natural climate variability.
We analyzed 7.5 years of our latest and best NASA satellite data and discovered that, when the effect of clouds-causing-temperature-change is accounted for, cloud feedbacks in the real climate system are strongly negative. The negative feedback was so strong that it more than cancelled out the positive water vapor feedback we also found. It was also consistent with evidence of negative feedback we found in the tropics and published in 2007.
In fact, the resulting net negative feedback was so strong that, if it exists on the long time scales associated with global warming, it would result in only 0.6 deg. C of warming by late in this century.
Even though they never say so, the IPCC has simply assumed that the average cloud cover of the Earth does not change, century after century. This is a totally arbitrary assumption, and given the chaotic variations that the ocean and atmosphere circulations are capable of, it is probably wrong. Little more than a 1% change in cloud cover up or down, and sustained over many decades, could cause events such as the Medieval Warm Period or the Little Ice Age.
As far as I know, the IPCC has never discussed their assumption that global average cloud cover always stays the same.