Comparison of the temperatures of stable, starless, thermally subcritical cores, with and without variable CO abundances. These cores are more nearly isothermal than the thermally supercritical cores (Fig. 5) because the gas does not couple with the dust and is cooled primarily by line radiation. The relative abundance of CO has been multiplied by 10 so that a value of 10 means undepleted. While the abundance of CO is quite low across the core, there is still a factor of 5 difference between the center and the edge. Parameters are listed in Table 1.