Abstract
<p>Despite an extensive literature on climate change news coverage, the long-form opinion and editorial journalism through which public arguments about climate policy are actively constructed has received comparatively little computational attention, particularly in the Australian context. This paper presents a longitudinal analysis of climate opinion discourse across five major English-language publications, comprising 28,801 articles from The Guardian (Australian edition), The Age, the Sydney Morning Herald, The Canberra Times, and The Australian spanning 1987 to 2026. Thematic structure was identified using BERTopic paired with a long-context sentence embedding model capable of encoding full editorial texts without truncation, recovering 66 coherent topics grouped into 8 thematic categories. Differential topic attention was assessed using binomial representation ratios and z-scores. Letters to the editor (n = 1,238) were projected into the fitted topic space and treated as a sixth analytical unit. The results reveal a structural partition between outlets: The Guardian is significantly over-represented across all seven globally oriented topic groups including Energy Transition &amp; Technology, Nature, Ecosystems &amp; Food Systems, and Climate Science, while the four Australian mastheads concentrate their coverage overwhelmingly in Australian Politics &amp; Policy. Letter writers align with the domestic orientation of the Australian titles, with significant over-representation only in Australian Politics &amp; Policy and near-absence from every internationally framed group. These findings provide the first computational characterisation of Australian climate opinion journalism at scale, documenting systematic outlet-level differences in thematic emphasis that are not reducible to differences in corpus size, and establishing a baseline for subsequent framing and stance analyses.</p>