[Editor: Due to the political nature of this question, the answerer wished to remain anonymous.]

My personal view is that the climate guys do have their act together on this. The 2007 United Nations Intergorvernmental Panel on Climate Change (IPCC) report says the probability that observed climate trends are man-made is "very likely". The IPCC defines "very likely" as 90-99%. (See "summary for policy makers" on Wikipedia.) The evidence is huge piles of understanding and studies, the vast majority of which indicate the same thing to one degree or another. I don't think they say this is "irrefutable"; IPCC didn't use their "virtually certain" (>99%) category. It is a policy issue to decide at what level of probability one should act.

[Editor: I would add that virtually all the studies cited by the IPCC are climate modeling studies based on mathematical computer models of global climate trends. Evidence is created by running the models with "natural" non-anthropogenic forcing variables only to find the temperature stays more or less constant. They then take the same model and put in anthropogenic forcing factors and they get a big effect in the model's predictions. This is the evidence.]