The aim of this paper is to observe, using discourse analysis methodologies, the process of debating system about climate questions through the agency of three notions: expertise, controversy and polemic. We propose to analyze the construction of climate change discourse in French medias and in scientists’ discourses through two discursive types: controversy and polemic, always regarding the part played by the climate expertise. The first part of this article helps to define discursively speaking what is controversy and what is polemic. It also constructs the links between these types of discourse and the definition of expertise. The empirical part of the article shows three complementary analysis: the uses of the two notions controversy and polemic in scientists’ discourses, a diachronic analysis of French media discourses regarding the IPPC representation and a synchronic analysis of French newspapers front pages from November 2009 and April 2010, focusing on the elements constructing the polemic and controversial discourses.