That's absurd. You are in effect arguing that any specialisation, in any area of science, inevitably leads to bias "and thereby science is diminished". Science depends on specialised study to advance knowledge. It's a good job you don't run any university science departments. You would accuse them of bias and shut them all down. It should be obvious that any study of man-made climate effects relies on first modelling the natural climate, so that the effects of human activity can be isolated and superimposed on it as a background. It is daft to imagine you can study man-made effects in isolation, apart from the detailed study of specific elements of the mechanisms involved, say the rate of release of methane from livestock or something. So nobody needs you to point out that man-made climate effects are a subset of all climate effects. And the accusation you make, that the IPCC "refuses to look at or see any other subsets", is quite fatuous. I do not believe you will be able to produce any credible evidence of this. All you will be able to do is seek out, from websites with a denial agenda, obscure bits and pieces which might, superficially at least, seem not to fit the model, to someone like yourself who does not know much science. Just like a creationist, in fact.