Testing the Link between Tropical Pacific Variability and Antarctic Climate Change

Abstract:

The recent expansion in Antarctic sea ice and the reported hiatus in global warming are at odds with CMIP5 model responses to anthropogenic forcing. Several studies have looked to the cooling of the central and eastern Tropical Pacific from 1980 - 2013 as potential drivers of these unexpected trends, via Rossby wave teleconnections and increased ocean heat uptake in the subtropical Pacific. Rossby waves emanating from the tropical Pacific are known to impact high latitudes, but their role in the recent expansion of Antarctic Sea ice is still a subject of debate. Furthermore, the wind-driven cooling of the tropical Pacific may change the rate of surface warming through an increase in ocean heat uptake, thus the Pacific may also be causing the reported hiatus. We test both of these hypothesis in two experiments carried out with a coupled ocean-atmosphere model, the Community Earth System Model 1.1. The first method uses an energy conserving flux adjustment to reproduce the observed cooling in the central and eastern tropical Pacific. The second method introduces a new tool to CESM; it adds an anomalous wind stress to the tropical Pacific while preserving the atmosphere-ocean coupling.

We find that both forcing methods are able to simulate a cooling trend in the tropical Pacific and the attendant changes in tropical convection. Yet neither method reproduces a slowdown in global warming. Furthermore, the teleconnections to Antarctica show a modest effect on sea ice extent, but do not fully account for the recent expansion in Antarctic Sea Ice.

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