(Part of the How to Talk to a Global Warming Skeptic guide)
Objection: More and more, climate models share all the same assumptions — so of course they all agree! And every year, fewer scientists dare speak out against the findings of the IPCC, thanks to the pressure to conform.
Answer: The growing confluence of model results and the increasingly similar physical representations of the climate system from model to model may well look like sharing code or tweaking ’til things look alike. But it is also perfectly consistent with better and better understanding of the underlying problem, an understanding that is shared via scientific journals and research. This understanding is coming fast as we gather more and more historical and current data, all of which provides more testing material for model refinement.
Viewing the increasing agreement among climate models and climate scientists as collusion instead of consensus is a rather conspiratorial take on the normal course of scientific investigation. I suppose that fewer and fewer scientists disagreeing with the status quo is indeed consistent with some kind of widespread and insidious suppression of ideas, but you know, it is also consistent with having the right answer.