They MUST have a dominating positive feedback mechanism else their possition falls flat on it's face.  As the years go by with increasing CO2 and stable temperture it becomes more and more apperent that such a thing simply does not exist and very possibly the opposite (negative feedback aka dampening) does exist.

The last of dozens of excuses I heard is that someone found a hot spot in the middle atmosphere in the Indian ocean area where there is little monitoring and that finally validates the concept of a positive feedback loop somehow.  These people seemed to have had to run that data through a series of statistical analysis methods in a (possibly trial-and-error) effort to find one which worked.  As a non-scientist it seems kind of intuitive to me that 20 years of excess thermal energy would be less difficult to identify were it contained in a small part of the atmosphere.  Just saying.  Whatever the case I am confident that the brilliant scientist who made this breakthrough will find plenty of grant money and department chair positions in their future.

http://wattsupwiththat.com/2015/05/14/claim-climate-scientists-find-elusive-tropospheric-hot-spot-over-the-southern-ocean/