IPCC likelihood ladder — the calibrated tier convention in high-stakes science communication

Claim: The IPCC uses a fixed, defined ladder of likelihood terms. Per AR6 and the Mastrandrea et al. (2010) Guidance Note:

• virtually certain: 99-100% probability
• very likely: 90-100%
• likely: 66-100%
• about as likely as not: 33-66%
• unlikely: 0-33%
• very unlikely: 0-10%
• exceptionally unlikely: 0-1%

Designed precisely to communicate graded confidence without false precision.

Source: IPCC AR6; Mastrandrea et al. 2010. Verified.

Why this matters for Candid: The widget's 4 difficulty tiers are this pattern applied to a different domain. Each tier label should map to a defined input range and a stable interpretation — like the IPCC ladder, not loose marketing-speak.