Success in initialization will be essential if geographical resolution is to be improved. Initialization focuses attention on the evaluation of model results and the intercomparison of models. As we resolve finer-scale issues, such as ocean eddies, these accomplishments will raise afresh the issues of coupling shock and model initialization. In such investigations, hybrid schemes should be considered in which low-resolution atmospheric models might be used in the initial stage of coupling. The questions of coupling and initialization are so closely connected with the long-term prediction problem of climate and of CO2 uptake by the oceans (and the terrestrial biosphere) that they must be central in future modeling work.

There are large differences in GCMs with respect to the scales of cloud microphysics and the treatment of these processes. There also tends to be a very real difference in focus between those models addressing the climate system at the large scale and those focused on small-scale processes as they occur in reality. To clarify the role of clouds in models, a hierarchy of models and observations needs to be used, and there should be greater emphasis on studies to isolate specific cloud processes. Finally, it would be useful to have a benchmark set of cloud and radiation diagnostics to be used to analyze feedbacks and compare models with observations.

The oceans are very energetic on spatial scales of 10 to 100 km, yet these motions are not resolved in the current generation of global climate models. A major unsolved problem in oceanography is to determine the effects of these unresolved mesoscale ocean eddies on large-scale circulation and climate.

The WOCE and JGOFS datasets of carbon and CFCs in combination with the ocean topography from the Ocean Topography Experiment (TOPEX/ Poseidon)91 and the current and next generation of satellite ocean color products, 92 as well as a number of existing seasonal, global-scale syntheses of nutrients, dissolved oxygen, surface carbon dioxide, and chlorophyll, present an unprecedented opportunity for evaluating models of the marine carbon cycle and extending our knowledge of its current state and potential future states. This is, as stated repeatedly, a central effort for the next decade.

THE ATMOSPHERIC PHYSICAL-CHEMICAL SUBSYSTEM

Overview

As we have noted throughout this report, important future changes of the Earth system will probably result, in part, from increasing atmospheric concentrations of greenhouse gases such as carbon dioxide, CFCs, methane, and nitrous oxide. These substances have biological, industrial, and other anthropogenic sources. In addition to their direct radiative effect, some of these gases undergo atmospheric chemical and photochemical transformations that alter the natural balance of other atmospheric gases. An important example is ozone, whose



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