Natural climate variabilities and Antarctic sea ice trend

Abstract:

The interannual Antarctic sea ice variability in Indian Ocean shares a large portion of variance with Southern Annular Mode (SAM), and that in Ross Sea with El Niño Southern Oscillation (ENSO). If we regress out the influence of these climate modes from the sectorial sea ice extent time series, the expanding sea ice trends in the satellite era become insignificant at 95 %. Because SAM has a human-induced trend, the increasing sea ice extent in Indian Ocean may be explained by superposition of anthropogenic forcing and natural variability. On the other hand, because ENSO does not have a significant trend, the sea ice trend in Ross Sea might be produced purely by natural variability. In addition to SAM and ENSO, some residual sea ice variances can be explained by other modes, which are not simultaneously-correlated with SAM or ENSO. For instance, a wave-like mode that appears to be Rossby wave trains shares large variance with interannual sea ice variability in many longitudinal sectors. The spatial trend pattern reconstructed by the Rossby mode exhibits consistent features with the ice motion trend pattern shown by Holland and Kwok (2012). These results, based on observational and reanalysis data, suggest that a large portion of expanding trend of Antarctic sea ice may be explained by natural climate variability.