These graphs show changes in average summer sea level pressure from one 25-year epoch to the next, for four epochs of CSM transient model output from 1874-1973. This output is from a full-forcings (solar irradiance, volcanic aerosols, tropospheric sulfates, and greenhouse gasses) integration over the instrumental period (1870-1999), which is a pilot run for a sequence of experiments designed to extend transient runs with full forcings over the 500-year period 1600-2100.

The reduction in average pressure over the interior North American Southwest in the second panel is concurrent with increased average summer precipitation in the eastern Southwest over the same time periods (not shown), suggesting that an enhanced monsoon circulation is playing a role in the precipitation change.