ABSTRACT
Donald Rumsfeld, the 2001-2006 US Secretary of Defence, was known to opine on
the strategy of war that there are “known knowns”, “known unknowns” and
“unknown unknowns”. It is assumed in this chapter that, while it is not possible to
prepare for unknown unknowns, and the known knowns are a given, the real
interest must lie in the known unknowns. Perhaps it is oxymoron to talk about
“known unknowns”, but it is usually possible to put a number on those unknowns,
which is termed “uncertainty”. In many circumstances the uncertainty can be more
disconcerting than the known knowns of a process. For example, while it might be
possible to plan for a 0.34-m sea-level rise on average in the next 100 years, it
becomes harder when it is acknowledged there is a range of uncertainty in this
estimate, 0.18-0.59 m (IPCC, 2007). While these extrapolations are based on linear
trends, what is more alarming is the uncertainty in the uncertainty – that is, it
remains unknown whether the uncertainty estimates should allow for long-term
exponential increases instead of linear extrapolations.
