Increased Indian Ocean-North Atlantic Ocean Warming Chain under Greenhouse Warming

Abstract Over the last half century, the Indian Ocean (IO) and the North Atlantic Ocean (NA) have shown strong warming trends that affected global and regional climates. Here, we investigate a closed linkage mechanism in warming between the two oceans by performing an Earth system model simulation. On the one hand, IO warming increases sea surface temperature (SST) over the NA by enhancing the warm oceanic advection around South Africa along with longwave radiative fluxes through upper tropospheric teleconnection. On the other hand, the warmer NA SST-induced atmospheric teleconnection leads to anomalous easterlies over the western Pacific, where sea level increases. The enhanced contrast in the sea levels of the Pacific and IO intensifies Indonesian throughflow, which increases ocean heat transport from the Pacific and warms the IO. This positive interaction (the IO-NA warming chain) reinforces further warming over both ocean basins. The IO-NA warming chain is projected to intensify due to a higher background SST under future climatic conditions with strong anthropogenic forcing, reducing precipitation over the western U.S. by 20%–50%.