So can you quantify that for us. Is it 5%, 10%, 50% or 100%? I am positive the fear-mongering models assume it is nearly 100% and further assumes some acceleration factors in there for good measure. It is really hard to scare people without some exponentially accelerating factors put in. Do you agree with their assumptions?
Since I used the term "qualitative", quantifying it would be a mistake. The IPCC Third Report said "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities." If most of the warming is attributable to human activities, then the human contribution is certainly not neglible, as I stated.
In many other FR discussions, I have pointed out that climate scientists have considered other climate forcing factors, such as solar activity and volcanoes, for the global climate since the mid-1850s. When you run the models using the known forcings from these, the models do not produce the observed warming. If anthropogenic CO2 is added, the models are close to the observed warming. If one asserts that anthropogenic CO2 is not to blame for the warming, then another "mytery" forcing of the same magnitude has to be found to replace it.