Science advisory committees exercise complex collaborative expertise. Not only do committee members collaborate, they do so across disciplines, producing expert reports that make synthetic multidisciplinary arguments. When reports are controversial, critics target both report content and committee process. Such controversies call for the assessment of expert arguments, but the multidisciplinary character of the debate outstrips the usual methods developed by informal logicians for assessing appeals to expert authority. This article proposes a multi-dimensional contextualist framework for critical assessment and tests it (...) with a case study of the controversies over reports issued by the Intergovernmental Panel on Climate Change. The case study shows (1) how the critical contextualist framework can illuminate the controversy and guide evaluation of the various arguments and counterarguments; (2) how cases of this sort open up avenues for fruitful interdisciplinary collaboration between argumentation theorists and other fields; and (3) where further work is required in argumentation theory. (shrink)