Process studies and related field efforts must be directed to improving our understanding and parameterization of surface-atmosphere interaction. Obviously, it is through this boundary interaction that slower-scale components communicate their influences to the atmosphere. Appropriate parameterization of these phenomena is therefore essential, since modeling efforts are the primary tool we have for forecasting future change. We also need better parameterization of clouds, including their distribution and feedback processes, because their treatment in models may prove crucial in predicting long-term climate responses to changes in radiative forcing, as well as other feedback influences associated with variability and change. These parameterizations are currently a primary limitation in existing models.
The radiative effects of aerosols, direct and indirect, are poorly constrained. Cloud processes, although they occur on far shorter than decadal timescales, are a major uncertainty in predicting future radiation balances. Parameterizations need to be improved.
Carbon cycle questions require a CO2 measurement strategy that accounts for the hierarchy of scales, both temporal and spatial, inherent in ecosystem processes and their controls. Atmospheric concentration data must allow the identification and quantification of regional sources and sinks and their responses to climate fluctuations and human perturbations. This information will permit integration over regional scales of fluxes and feedback processes that can be measured, understood, and modeled on smaller spatial and temporal scales. Isotopic data allow distinguishing between oceanic and biospheric sinks on regional scales and have provided significant insight into the regional carbon balance. Ratios of O 2 to N2 in the global atmosphere provide an independent constraint on the balance between net terrestrial and oceanic sinks. The same scaling and measurement issues are almost identical for N2O and CH4, and their biogeochemical budgets can be tackled together with a measurement program suitable for CO2.
Enormous progress in assessing trace gas budgets could be achieved if a method could be developed or refined to directly measure air-sea gas exchange rates. Promising methods are air measurements with eddy correlation and/or eddy accumulation. Such measurements would eventually lead to a realistic understanding of the processes controlling the rate of gas exchange and therefore to a parameterization that could be applied with confidence worldwide. Existing climatologies of the partial pressure differences between the air and the water for many gases could then be turned into maps of gas exchange, making oceanic data into a much more compelling constraint on the atmospheric budget and closing the open boundary of surface oceanic gas budgets.