Worldwide atmospheric concentrations of heat-trapping greenhouse gases have been rising at a relatively uniform rate, but tropical oceans respond to higher carbon dioxide (CO₂) levels in different ways. In the tropical Pacific, the sea-surface temperature responds with enhanced equatorial warming compared to the subtropics. However, the tropical Indian Ocean exhibits reduced warming in its eastern equatorial area and increased warming in the western area. Three scientists, including a Department of Energy researcher from the Pacific Northwest National Laboratory, set out to isolate and analyze the formation of this Indian Ocean dipole (IOD) phenomenon using a partial coupling technique in a global climate model by overriding the wind speed or wind stress from certain climate scenarios. The design of the overriding experiments enabled them to isolate atmospheric feedback phenomena such as Bjerknes and WES (wind-evaporation-sea surface temperature) and identify the ocean warming response to double CO₂ concentrations without interference. As baselines for the experiments, they used the Community Climate System Model version 3 (CCSM3) to perform control runs either with present-day data or with double CO₂. By isolating the effects of the Bjerknes and WES feedbacks, which involve the southeasterly winds along Sumatra, they found an IOD-like pattern, which was most pronounced in July-October. Both feedbacks are clearly essential to the dipolar warming pattern because, when they are removed from the model, leaving only the “static” responses to increasing CO₂, the pattern disappears. The scientists also noted that, while these results can be generalized qualitatively to most climate models, the quantitative contributions from these two feedbacks should be treated with caution.