An assessment and interpretation of the observed warming of West Antarctica in the austral spring

Abstract

We synthesize variability and trends in multiple analyses of Antarctic near-surface temperature representing several independent source datasets and spatially complete reconstructions, and place these into the broader context of the behavior of other components of the climate system during the past 30-50 years. Along with an annual-mean trend during the past 50 years of about 0.1°C/decade averaged over Antarctica, there is a distinct seasonality to the trends, with insignificant change (and even some cooling) in austral summer and autumn in East Antarctica, contrasting with warming in austral winter and spring. Apart from the Peninsula, the seasonal warming is largest and most significant in West Antarctica in the austral spring since the late 1970s. Concurrent trends in sea ice are independent evidence of the observed warming over West Antarctic, with the decrease in sea ice area in the Amundsen and Bellingshausen Seas congruent with at least 50% of the inland warming of West Antarctica. Trends in near surface winds and geopotential heights over the high-latitude South Pacific are consistent with a role for atmospheric forcing of the sea ice and air temperature anomalies. Most of the circulation trend projects onto the two Pacific South American (PSA) modes of atmospheric circulation variability, while the Southern Annular Mode lacks a positive trend in spring that would otherwise cause a cooling tendency. The largest circulation trend is associated with the PSA-1 mode, a wave-train extending from the tropics to the high Southern latitudes. The PSA-1 mode is significantly correlated with SSTs in the southwestern tropical and subtropical Pacific. The increased SSTs in this region, together with the observed increase in rainfall, suggest that anomalous deep convection has strengthened or increased the occurrence of the Rossby wave-train associated with PSA-1. This hypothesis is supported by results from two ensembles of SST-forced atmospheric general circulation model simulations. Finally, the implications of the seasonality, timing, and spatial patterns of Antarctic temperature trends with respect to interpreting the relative roles of stratospheric ozone depletion, SSTs and increased atmospheric concentrations of greenhouse gasses are discussed.

The Influence of the Amundsen–Bellingshausen Seas Low on the Climate of West Antarctica and Its Representation in Coupled Climate Model Simulations

“…Perhaps the most persuasive evidence is a recently compiled reconstruction of SAT for Byrd Station in central West Antarctica (808S, 1208W), which revealed an annually averaged warming rate of ;0.58C decade 21 between 1958 and 2010, substantially greater than the global average (Bromwich et al 2013). Pronounced warming of this region over the past ;100 years has also been detected from ice cores (Schneider and Steig 2008). Recent regional sea ice change reflects further evidence of significant climate change in this region.…”

Is a bipolar seesaw consistent with observed Antarctic climate variability and trends?

“…A bipolar seesaw is not needed to explain the lack of warming in some regions and seasons in Antarctica [Marshall, 2007;Schneider et al, 2012a]. However, both the SAM and Antarctic temperature trends have a marked seasonality, and there has been significant regional warming in the western Antarctic Peninsula and West Antarctic Ice Sheet [Schneider et al, 2012a]. These seasonal and regional warming patterns are linked with atmospheric circulation changes in the South Pacific that are consistent with the observed pattern of tropical and extratropical SST trends [Schneider et al, 2012a;Ding et al, 2011].…”

“…The pattern of SST trends since 1979 (Figure 2, bottom right) in part reflects tropical variability and the transition from a warm to a cool tropical phase over recent decades that is evident in the OTI and PDO indices (Figure 1d). This is associated with an atmospheric teleconnection in the South Pacific (Figure 2, bottom left) that resembles the circulation patterns identified by Schneider et al [2012a] and Ding et al [2011]. Thus, while Antarctic climate is responsive to forcing by stratospheric ozone depletion and greenhouse gas increases [e.g., Gillett et al, 2008], natural variability has likely played a role in recent trends.…”

“…However, both the SAM and Antarctic temperature trends have a marked seasonality, and there has been significant regional warming in the western Antarctic Peninsula and West Antarctic Ice Sheet [Schneider et al, 2012a]. These seasonal and regional warming patterns are linked with atmospheric circulation changes in the South Pacific that are consistent with the observed pattern of tropical and extratropical SST trends [Schneider et al, 2012a;Ding et al, 2011]. The pattern of SST trends since 1979 (Figure 2, bottom right) in part reflects tropical variability and the transition from a warm to a cool tropical phase over recent decades that is evident in the OTI and PDO indices (Figure 1d).…”

“…Since 1979, Antarctic temperature trends are essentially zero, though there are notable regional exceptions, including strong warming in the Peninsula and West Antarctica [Schneider et al, 2012a]. The mixed signals from Antarctica stand in sharp contrast to the rapid warming of nearly the entire Arctic in recent decades [e.g., Turner and Overland, 2009].…”