Page 4: Climate model evaluation and improvement
The sensitivity of climate models, and hence the transient behavior to perturbations, depends very strongly on the initial state; thus transient coupled atmosphere-ocean general circulation model experiments aimed at simulating the Younger Dryas event will be difficult. In contrast, efforts to simulate the time-dependent patterns of change associated with abrupt events of the Holocene (see Section 2.4) may be more likely to succeed. Careful work will still be needed to define initial model states, as well as to define the exact time-space nature of the abrupt events. Here the information collected for simulating past extreme conditions (see PMIP above) will prove useful. In particular, the hydrological cycle and its large-scale changes should be better known. Again, a hierarchy of models should be employed to study individual feedback mechanisms and their importance in determining sensitivity, variability, and abrupt change in these models.	Detecting Change. A key issue in climate research is the extent to which various hypothesized natural and anthropogenic forcing mechanisms have affected the last 150 years of climate variability. This question cannot be answered definitively, however, until the full range of natural decade- to century-scale variability is understood. This goal will be a point of PAGES-CLIVAR intersection.