J. Clim. 30, 1971–1983 (2017)

Historically, patterns of decadal sea-surface temperature (SST) variability in the Indian and Pacific Oceans have been strongly connected. This is because warm anomalies in the Pacific Ocean (positive phase of the interdecadal Pacific oscillation, IPO) force warmth in the Indian Ocean (positive phase of the Indian Ocean basin mode, IOB) through coupled air–sea interactions. However, since 1985, this relationship has broken down, the cause of which is not well understood.

Lu Dong and Michael McPhaden from the NOAA Pacific Marine Environmental Laboratory, USA, investigate the factors causing this change in SST relationships using observations and coupled climate model simulations. They demonstrate that the perturbed IPO–IOB association can largely be attributed to increased external forcing by greenhouse gases. Specifically, they find that greenhouse gas forcing has warmed the Indian Ocean, overwhelming changes that would have arisen from the IPO, and thus weakening dynamical links between the two ocean basins. Indeed, in the absence of anthropogenic forcing, model simulations suggest that IOB evolution would have remained strongly connected to the IPO. These shifting ocean interactions have implications for understanding regional sea-level rise and the global warming 'hiatus', emphasizing the need to further examine inter-basin interactions under climatic change.