Decadal time scale fluctuations in the Pacific Ocean are linked to modulation of the El Nino/Southern Oscillation (ENSO) cycle and have significant impacts on the climate of North America. However, the characteristics of these fluctuations in the ocean are poorly documented and the physical mechanisms responsible for them are poorly understood. This presentation briefly reviews theories for Pacific decadal climate variability, then uses observations over the past 50 years to test aspects of those theories that relate to interactions between the tropical and subtropical oceans. Results indicate that the shallow wind-driven meridional overturning circulation has been spinning down since the 1970s and that, as a consequence, equatorial upwelling has decreased by 25%. This reduction in upwelling is associated with a rise in equatorial sea surface temperatures of about 0.8°C, and with a significant reduction in the outgassing of CO2 from the equatorial Pacific Ocean to the atmosphere. Implications of these results for models and theories of decadal variations in the Pacific ocean-atmosphere system will be discussed.