central illustrative value of £70/tC only, whilst some used the illustrative range
of £35 to £140/tC. There were also a few cases where a single value at the upper
or lower end of the range was used. During the interviews, the reason for this
variation was explored: in some cases this reflected the view that the analyst
held on the robustness of the SCC value. What is clear is that the use of different
values leads to inconsistency, and this has implications for the cost-effective
introduction of GHG strategies across different policy areas. Importantly it provides
a key point for appraisal in the future (in the UK and elsewhere)—there
is a trade off between using a range of values to reflect the likely uncertainty,
compared to the use of a central value (only) to ensure consistency.