Contributions of Greenhouse Gas Forcing and the Southern Annular Mode to Historical Southern Ocean Surface Temperature Trends. Issue 2 (30th January 2018)

• Record Type: Journal Article
• Authors: Kostov, Yavor; Ferreira, David; Armour, Kyle C.; Marshall, John
• Is Part Of: Geophysical research letters. Volume 45:Issue 2(2018)
• Page Start: 1086
• Page End: 1097
• Publication Date: 2018-01-30
• Subjects: Southern Ocean -- CMIP5 -- Southern Annular Mode -- greenhouse gas forcing -- climate variability -- ozone forcing; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL074964
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We examine the 1979–2014 Southern Ocean (SO) sea surface temperature (SST) trends simulated in an ensemble of coupled general circulation models and evaluate possible causes of the models' inability to reproduce the observed 1979–2014 SO cooling. For each model we estimate the response of SO SST to step changes in greenhouse gas (GHG) forcing and in the seasonal indices of the Southern Annular Mode (SAM). Using these step‐response functions, we skillfully reconstruct the models' 1979–2014 SO SST trends. Consistent with the seasonal signature of the Antarctic ozone hole and the seasonality of SO stratification, the summer and fall SAM exert a large impact on the simulated SO SST trends. We further identify conditions that favor multidecadal SO cooling: (1) a weak SO warming response to GHG forcing, (2) a strong multidecadal SO cooling response to a positive SAM trend, and (3) a historical SAM trend as strong as in observations. Key Points: CMIP5 models have diverse Southern Ocean SST response functions to SAM and greenhouse gas forcing Weak warming (strong cooling) responses to greenhouse gas forcing (SAM) favor multidecadal Southern Ocean cooling Biases in the simulated SAM trends strongly affect the models' historical Southern Ocean SST trends