Divergence in Climate Change Communication: LLM-Based Evidence from the IPCC and the Press

Public summaries of IPCC climate assessments lean toward the more severe end of the technical evidence. The pattern appears at two stages: the IPCC’s lead authors and member governments produce the Summary for Policymakers (SPM) from the Technical Summary (TS), and newspapers then cover the SPM. We use LLMs to score about 114,000 matched claim pairs from all six Assessment Reports (1990 to 2023) and ten major US and UK outlets. Both stages systematically shift toward the more severe end of the source while staying inside the IPCC’s accepted scientific ranges. The shift comes mainly from emphasizing higher-impact magnitudes within reported ranges, less from uncertainty compression, and almost none from selecting worst-case emissions scenarios. Left- and right-leaning outlets show similar patterns.