Changes in atmospheric circulation over the past five decades have enhanced the wind-driven inflow of warm ocean water onto the Antarctic continental shelf, where it melts ice shelves from below. Atmospheric circulation changes have also caused rapid warming over the West Antarctic Ice Sheet, and contributed to declining sea-ice cover in the adjacent Amundsen-Bellingshausen seas. It is unknown whether these changes are part of a longer-term trend. Here, we use water-isotope (δ 18 O) data from an array of ice-core records to place recent West Antarctic climate changes in the context of the past two millennia. We find that the δ 18 O of West Antarctic precipitation has increased significantly in the past 50 years, in parallel with the trend in temperature, and was probably more elevated during the 1990s than at any other time during the past 200 years. However, δ 18 O anomalies comparable to those of recent decades occur about 1% of the time over the past 2,000 years. General circulation model simulations suggest that recent trends in δ 18 O and climate in West Antarctica cannot be distinguished from decadal variability that originates in the tropics. We conclude that the uncertain trajectory of tropical climate variability represents a significant source of uncertainty in projections of West Antarctic climate and ice-sheet change.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation Office of Polar Programs (grant numbers 0537930, 0837988, 0963924 and 1043092 to E.J.S.; 05379853 and 1043167 to J.W.C.W.; 0944730 to S.B.R.; 0230396, 0440817, 0944348 and 0944266 to K.C.T.; 0096305, 9316564, 0096299, 0424589, 0439589, 063740, 063650 and 0837883 to P.A.M.; 0838871 to D.P.S.). NCAR is sponsored by the National Science Foundation. We thank A. Orsi, J. Bautista and J. Flaherty.