A hierarchy of atmospheric general circulation model simulations of the 1950--1994 period that employ different prescriptions of the oceanic boundary conditions are analyzed. It is demonstrated that contrary to expectations, increased spatial coverage of the sea surface temperature specification can degrade the underlying simulated climate signals. The cause for this is related to an inability to accurately model the diversity of air-sea interaction regimes that exist across the global oceans. Such failure is shown to generate spurious sources of atmospheric energy that exert global influences on interannual and decadal timescales. ¿ 1998 American Geophysical Union