IPCC (2007c) discusses some other strategies that are also used to estimate or bound model uncertainties.

Figure 1.7 shows which aspects of climate can be most robustly predicted, separated by phenomenon and time scale, based on such assessments. In general, climate models more robustly predict trends at larger space and time scales, and they predict temperature trends more reliably than precipitation trends. They all project a reduction in summer sea-ice extent, but not as large as that observed in recent years. They robustly predict the contribution to global sea-level rise from heat uptake in the oceans, but most do not include a representation of ice-sheet melt and the disintegration of the tongues of large glaciers that may considerably accelerate sea-level rise over the next century. They agree that the polar regions will become wetter and that the subtropics will become drier, but they do not agree on which regions of the subtropics will experience strong drying. As climate models become more comprehensive and their grid scale becomes finer, they can provide meaningful projections of more parts of the climate response and their possible feedbacks on the overall climate system, but this does not necessar-


FIGURE 1.7 Time and space scales of key climate phenomena. Color coding shows relative reliability of climate model simulations of these phenomena (or their statistics in the present climate, for climate variability/extremes).


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