Developing an Ad Hominem typology for classifying climate misinformation

Misinformation produced by various interest groups is a significant contributing factor to public confusion about climate policy. Character assassination against climate scientists and policymakers is the most common type of misinformation strategy used by contrarians in climate debates (Coan, T. G., Boussalis, C., Cook, J., & Nanko, M. O. (2021). Computer-assisted classification of contrarian claims about climate change. Scientific Reports, 11(1), 22320). Despite its widespread use, however, character assassination remains understudied by social scientists, especially in the context of climate change. This study adapts Douglas Walton's (1998. Ad hominem arguments. University of Alabama Press) typology of 'ad hominem' attacks - personal attacks targeting an individual's character, competence, or motives - to misinformation campaigns against the climate community. We developed an original codebook for classifying ad hominem arguments made by climate contrarians. Drawing on a 553-paragraph sample from a corpus from 55 contrarian blogs and 15 conservative think-tank websites published in English between 2008 and 2020, we then determined the relative prominence of each type of attack using a consensus-coding approach. Bias attacks, which entail accusing climate scientists of political partisanship or having an ideological agenda, were the most common form of contrarian ad hominem attack. The dominance of bias attacks can be explained by their strong relevance for scientific credibility. The study found that ad hominem attacks, often with bias and moral attacks clustered together, are the most common combination. The article concludes by discussing the implications of these findings for climate policy and future research.Key Policy InsightsClimate misinformation politicizes climate science, further amplifying ideological conflict and fostering ideological polarization;Climate misinformation campaigns feature a range of different types of ad hominem attacks designed to undermine the credibility of climate scientists;The most common type of ad hominem attack on climate scientists in our sample was bias attacks, which entail accusing climate scientists of political partisanship or of having an ideological agenda;Attacks on the moral character of climate scientists were the only type of ad hominem that increased during the period under study (2008-2020);Different types of ad hominems often appeared together, with the most common combination being bias and moral attacks;Ad hominem attacks on climate scientists are part of misinformation campaigns designed to stall discussion on climate change and delay the implementation of climate policies.