Evolution of the Southern Annular Mode during the past millennium

The Southern Annular Mode (SAM) is the primary pattern ofclimate variability in the Southern Hemisphere, influencinglatitudinal rainfall distribution and temperatures from thesubtropics to Antarctica. The positive summer trend in theSAM over recent decades is widely attributed to stratosphericozone...

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Bibliographic Details
Published in:Nature Climate Change
Main Authors: Abram, NJ, Mulvaney, R, Vimeux, F, Phipps, SJ, Turner, J, England, MH
Format: Article in Journal/Newspaper
Language:English
Published: Nature Publishing Group 2014
Subjects:
Earth Sciences
Physical geography and environmental geoscience
Palaeoclimatology
Antarctic
The Antarctic
Antarctic Peninsula
Pacific
Antarc*
Antarctica
Online Access:https://doi.org/10.1038/NCLIMATE2235
http://ecite.utas.edu.au/104734
Description
Summary:The Southern Annular Mode (SAM) is the primary pattern ofclimate variability in the Southern Hemisphere, influencinglatitudinal rainfall distribution and temperatures from thesubtropics to Antarctica. The positive summer trend in theSAM over recent decades is widely attributed to stratosphericozone depletion; however, the brevity of observational recordsfrom Antarctica-one of the core zones that defines SAMvariability-limits our understanding of long-term SAM behaviour.Here we reconstruct annual mean changes in the SAMsince AD 1000 using, for the first time, proxy records thatencompass the full mid-latitude to polar domain across theDrake Passage sector. We find that the SAM has undergone aprogressive shift towards its positive phase since the fifteenthcentury, causing cooling of the main Antarctic continent atthe same time that the Antarctic Peninsula has warmed. Thepositive trend in the SAM since ~AD 1940 is reproduced bymultimodel climate simulations forced with rising greenhousegas levels and later ozone depletion, and the long-term averageSAM index is now at its highest level for at least the past 1,000years. Reconstructed SAM trends before the twentieth centuryare more prominent than those in radiative-forcing climateexperiments and may be associated with a teleconnectedresponse to tropical Pacific climate. Our findings imply thatpredictions of further greenhouse-driven increases in the SAMover the coming century also need to account for the possibilityof opposing effects from tropical Pacific climate changes.

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