New paper finds another non-hockey-stick in Antarctica, temperature decline over past 2000 years

A new paper published in Nature Geoscience reconstructs temperatures of the West Antarctic ice sheet from ice cores and shows that temperatures have declined over the past 2,000 years. The proxy for temperature, an isotope of oxygen [d18O], shows a decline over the past 2,000 years [figure 3 below], and thus indicates a decrease in temperature. A blowup of the past 200 years [figure 2 below] shows that the d18O temperature proxy at the end of the record in ~2010 had been exceeded many times over the past 200 years, including during the 1800's, 1940's, and 1990's. 

The d18O proxy for temperature declined over the past 2,000 years, as also shown by the dotted line at the 97.5% percentile value relative to the average trend.

Blowup of the past 200 years [2nd graph from top] shows the d18O proxy at the end of the record in ~2010 had been exceeded many times over the past 200 years, including during the 1800's, 1940's, and 1990's. 

 Recent climate and ice-sheet changes in West Antarctica compared with the past 2,000 years

• Eric J. Steig,
• Qinghua Ding,
• James W. C. White,
• Marcel Küttel,
• Summer B. Rupper,
• Thomas A. Neumann,
• Peter D. Neff,
• Ailie J. E. Gallant,
• Paul A. Mayewski,
• Kendrick C. Taylor,
• Georg Hoffmann,
• Daniel A. Dixon,
• Spruce W. Schoenemann,
• Bradley R. Markle,
• Tyler J. Fudge, 
• David P. Schneider,
• Andrew J. Schauer,
• Rebecca P. Teel,
• Bruce H. Vaughn,
• Landon Burgener,
• Jessica Williams
• & Elena Korotkikh

Nature Geoscience

 

(2013)

 

doi:10.1038/ngeo1778

Received

 

11 July 2012 

Accepted

 

26 February 2013 

Published online

 

14 April 2013

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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^1, 2, 3. Atmospheric circulation changes have also caused rapid warming⁴ over the West Antarctic Ice Sheet, and contributed to declining sea-ice cover in the adjacent Amundsen–Bellingshausen seas⁵. It is unknown whether these changes are part of a longer-term trend. Here, we use water-isotope (δ¹⁸O) 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 δ¹⁸O 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, δ¹⁸O 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 δ¹⁸O 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.