Response of the Pacific Ocean Circulation to Climate Change

The response of the Pacific Ocean circulation to climate change is investigated by comparing solutions from a set of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled models for a present-day climate (the 20C3M experiments) and a future, warmer climate (the SRESA1B experiments). Under the warmer climate scenario, the oceanic changes in the tropical Pacific include a relatively weak warming of the western equatorial thermocline, a weakening of the surface current system and a complicated change in the structure of the Equatorial Undercurrent (EUC) with an increased flow in its upper branch but a decreased flow in its lower branch. As the climate warms, the North Pacific Ocean features a basin-scale reduction in mixed layer depth, a weakening of the subtropical countercurrent (STCC), a northward shift of the Kuroshio Extension (KE) and an overall slowdown of the subtropical gyre. In the South Pacific, the warmer climate induces significant changes in the upper ocean of the eastern subtropics including a relatively weak warming, a deepening of mixed layer depth and an anticylonic circulation.