Online Resource 4: Consistency of estimates with the prescriptions in Table 1.

Best estimates were labelled as consistent if they were within the range prescribed by the IPCC (Table 1). For example, best estimates for ‘unlikely’ were considered to be consistent if they were less than or equal to 33% (see Table A for consistency rates of best estimates)

Ranges were labelled as consistent if both upper and lower bounds were within the prescribed range, as inconsistent if both were outside the prescribed range, and as partially consistent otherwise. For example, endorsed ranges for ‘unlikely’ were considered to be consistent if the higher bound was 33% or lower, inconsistent if the lower bound was higher than 33%, and partially consistent if the lower bound was 33% or lower but the higher bound was greater than 33% (see Table B for consistency rates of endorsed ranges).

Note that there were no significant differences between conditions for any of the individual probability phrases, although all were numerically in the predicted direction.

Table A. Consistency of best estimates with the prescriptions of Table 1.

Single-anchor format / Two-anchor format
Probability phrase / Consistent / Inconsistent / Consistent / Inconsistent
IPCC very likely / 88% / 12% / 91% / 9%
IPCC likely / 89% / 11% / 93% / 7%
IPCC unlikely / 91% / 9% / 96% / 4%
IPCC very unlikely / 91% / 9% / 92% / 8%
IAS
likely / 92% / 8% / 97% / 3%
IAS unlikely / 92% / 8% / 96% / 4%
All terms / 90% / 10% / 94% / 6%

Table B. Consistency of endorsed ranges with the prescriptions of Table 1.

Single-anchor format / Two-anchor format
Probability phrase / Consistent / Partially consistent / Inconsistent / Consistent / Partially consistent / Inconsistent
IPCC very likely / 73% / 21% / 6% / 81% / 17% / 2%
IPCC likely / 71% / 25% / 4% / 75% / 24% / 1%
IPCC unlikely / 81% / 16% / 3% / 84% / 12% / 4%
IPCC very unlikely / 78% / 16% / 6% / 82% / 15% / 3%
IAS
likely / 75% / 23% / 2% / 79% / 20% / 1%
IAS unlikely / 81% / 16% / 3% / 86% / 13% / 1%
All terms / 77% / 19% / 4% / 81% / 17% / 2%