An expression of the degree to which a future condition (e.g., of an
ecosystem) is unknown.
Uncertainty can result from lack of information or from disagreement about
what is known or even knowable. It may have many types of sources, from
quantifiable errors in the data to ambiguously defined terminology or uncertain
projections of human behavior. Uncertainty can therefore be represented by
quantitative measures (e.g., a range of values calculated by various models) or
by qualitative statements (e.g., reflecting the judgment of a team of experts).
Millennium Ecosystem Assessment