FIGURE Q.1 Calculated surface temperature variation with changes in low-cloud cover and surface albedo.
in the arctic region to promote ice melting and improved growing conditions in Siberia. Before the more recent satellite measurements, most of what was known about cloud processes and how they contribute to the global radiative balance came from climate modeling, and in climate models, most of the details of the cloud processes were not included. Certainly, no individual clouds were included on the grid scale of the general circulation models (GCM); thus specific details of the microphysics, as it might involve seeding or CCN, could not be studied within the concept of GCMs.
In a recent paper, Albrecht (1989), following a hypothesis of Twomey and Wojciechowski (1969), grossly estimated the additional CCN that would be necessary to increase the fractional cloudiness or albedo of marine stratocumulus clouds by 4 percent. He estimates that this increase in low-level fractional cloudiness would be equivalent to that attributed to a 30 percent increase in CCN. As noted from Table Q.3, this 4 percent increase, if it were strictly in lower-level cloud abundance at global average conditions (35° latitude), would be more or less equivalent to the cloudiness at 4° latitude further north. Albrecht's idealized stratocumulus cloud, which he argues is typical, has a thickness of 375 m, a drizzle rate of 1 mm per day,