We consider the relative effectiveness of engineered systems for collection and marine disposal of CO2 from fossil-fuel-fired power plants using comparisons of the trend with time of CO2 concentration in the atmosphere from systems with and without marine disposal. Since the retention time for CO2 increases rapidly with depth of disposal, from a few years in the mixed layer up to several centuries as the depth increases beyond 1000 m, deep oceans have been considered as potential storage sites for CO2. However, CO2 Collection and disposal consumes energy and produces extra CO2. We show that some of this extra CO2 reaches the atmosphere, so that atmospheric concentrations from systems with marine disposal ultimately exceed those from systems without controls. In some circumstances, they do so rapidly, making marine disposal less favorable than direct atmospheric release. The Global Warming Potential (GWP) can be used to compare different systems, but results for GWP highlight the difficult issue of determining what time scales are important in considering options to reduce concerns about global warming.