well we will never be able to prove it in the same way as we can prove A=C, if A=B AND B=C, science doesnt work like that. the closer a model's predictions match real-world observations, the better the model is. the more climate models are refined, the closer they are in agreement with each other, and to the real-world measurements. its about weight of evidence, rather like legal prosecution. at this stage I'd personally say we have more than enough evidence to charge, but not quite enough to guarantee a conviction ...
