Adaptation to climate variability and change is important both for impact a
ssessment (to estimate adaptations which are likely to occur) and for polic
y development (to advise on or prescribe adaptations). This paper proposes
an "anatomy of adaptation" to systematically specify and differentiate adap
tations, based upon three questions: (i) adapt to what? (ii) who or what ad
apts? and (iii) how does adaptation occur? Climatic stimuli include changes
in long-term mean conditions and variability about means, both current and
future, and including extremes. Adaptation depends fundamentally on the ch
aracteristics of the system of interest, including its sensitivities and vu
lnerabilities. The nature of adaptation processes and forms can be distingu
ished by numerous attributes including timing, purposefulness, and effect.
The paper notes the contribution of conceptual and numerical models and emp
irical studies to the understanding of adaptation, and outlines approaches
to the normative evaluation of adaptation measures and strategies.