Bob Carter admits to not knowing the full extent to which water vapour responds to the climate but from what I gather attributes this as a big reason to why the IPCC model is so far wrong in predictions. While many agnostics do admit to the reality of the actual trends, I gather a large component of the disagreement (and LACK of concensus) is the role of water vapour, clouds and albedo and the inaccuracy of the IPCC model.
Albedo (as cloud cover) has an immediate effect on local temperatures. However albedo is altered also by particulates, such as volcanic disruptions. http://en.wikipedia.org/wiki/Albedo
IMO, the agnostic argument (to call it that) is based on being more open to better and more accurate modelling of heat and energy flows (sources and sinks) - and that these change in response to the changing conditions, not remaining static as projected by the alarmists.
