Recently analyzed ice core data from West Antarctica confirms warming since 1957, but shows two other warming episodes over the past three centuries suggesting that anthropogenic influences are within the range of natural variation of climate there.
Elizabeth Thomas and collaborators’ study focused on the coastal region of West Antarctica, important because of its proximity to rapidly shrinking glaciers and the West Antarctica Ice Sheet. Ice core drilled on the Bryan Coast was analyzed for deuterium (δD) to reconstruct a 308-year time series dating back to 1702. The δD time series is used to describe temporal variability but not assumed to be a quantitative temperature proxy. The δD record was significantly but poorly correlated with atmospheric temperature. Time series showed an isotopic warming of 2.7 degrees since 1957, coherent with other isotopic and instrumental records. However, even greater warming episodes of 4.1 degrees from 1740-1789 and 3.8 degrees from 1888-1839 were also observed. Results from other ice core on the Antarctic Peninsula in Ross Island (north of the Bryan coast) revealed a climatically different signal from that observed in West Antarctica ice core, where warming has been ongoing since 1920.
The authors concluded that climate variability at the West Antarctica site was influenced by subtropical high pressure and sea surface temperature anomalies in the central and west Pacific. A reconstruction of Pacific sea surface temperature and coral data were used to verify this tropical teleconnection. The study also shows the influence of meridional winds on the surface temperatures of the West Antarctic region. The dramatic warming trends observed during the mid-eighteenth and nineteenth centuries suggest that the warming of the last half century is within the natural range of climate variability within the past ~300 years for the West Antarctic area. The authors conclude that this area – identified by some as among the most rapidly warming regions on Earth – is part of the 20% of Earth’s surface where 100-year trends do not reflect warming beyond the bounds of natural variability.
Citation: Thomas ER, Bracegirdle TJ, Turner J, Wolff EW, 2013. A 308 year record of climate variability in West Antarctica. Geophysical Research Letters 40, 5492–5496, doi:10.1002/2013GL057782