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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 11, NUMBER 11, NOVEMBER 1998

PROFESSIONAL PUBLICATIONS...
POLAR CLIMATES

Item #d98nov7

“Antarctic Elevation Change from 1992 to 1996,” D. J. Wingham et al.,Science 282, 456-458 (1998).

The elevation of the Antarctic Ice Sheet as measured by satellite-borne radar altimeters decreased almost 1 cm/year between 1992 and 1996. Taking into account the variability of snowfall, this value would represent a decrease of only 0.06 ± 0.08 in the mass-accumulation rate. Some regional decreases were significantly greater than this average value. However, the mass of the icecap has generally been in balance during the past 1000 years.

Item #d98nov8

“Synchronous Climate Changes in Antarctica and the North Atlantic,” E. J. Steig (steig@colorado.edu) et al.,Science 282, 92-95 (1998).

Two ice cores, one from Antarctica and one from Greenland, were chronologically linked by identifying in each of them large, rapid changes in the atmospheric methane that got trapped in sequential ice layers. Then the stable- isotope ratios in the ice cores were studied to determine the temperature conditions under which the ice was created. The changes in temperature recorded during the past 100,000 years in the core from the Taylor Dome in Antarctica were almost identical to the changes in Greenland’s GISP 2 core during the same period. Specifically, the two sites present evidence of a warming event (about 20oF in about 50 years) that occurred about 12,500 years ago, which was previously thought to have occurred only (or at least primarily) in the Northern Hemisphere. Temperatures during this period, from the end of the Younger Dryas to the beginning of the Holocene, achieved this change in a series of major jumps that each occurred in less than a decade. This warming and its timing are confirmed by deep-sea sediment patterns that indicate significant changes in the North Atlantic’s circulation (and, thus, climate). Other ice cores from Antarctica do not show this same climate pattern, but it is believed that they were sheltered from the climatic effects by being well inland.

Item #d98nov9

“Past Temperatures Directly from the Greenland Ice Sheet,” D. Dahl-Jensen (ddj@gfy.ku.dk) et al.,Science 282, 268-271.

High-precision equipment was used to measure small temperature variations within the Greenland Ice Sheet that resulted from past climatic changes. Measurements down the Greenland Ice Core Project (GRIP) borehole resulted in a temperature record that extended back 50,000 years. Measurements down the Dye 3 borehole resulted in a temperature record that extended back 7,000 years. The two sites yielded parallel results, but the amplitude of the Dye 3 temperature changes was 1.5 times that of the GRIP changes indicating a greater climate variability at the Dye 3 site. Temperatures in central Greenland were found to be 2oF colder than present during the Little Ice Age (1420 to 1890 AD), 2oF warmer than present 1,000 years ago during the Medieval Warm Period, 4.5oF warmer 5000 years ago, and 41oF colder than current values about 22,000 years ago during the last ice age.

Item #d98nov10

“North Atlantic Oscillation Dynamics Recorded in Greenland Ice Cores,” C. Appenzeller (christof.appenzeller@climate.unibe.ch), T. F. Stocker, and M. Anklin,Science 282, 446-449 (1998).

The North Atlantic Oscillation (usually expressed as an index value) is a variation in the pressure difference between the areas of Iceland and the Azores. Those variations have a strong influence on North Atlantic and European weather. Ice core data from Greenland were studied to reconstruct the NAO index for the past 350 years. The data indicate that the NAO is an intermittent phenomenon with active and inactive phases. No evidence was found that the NAO occurred with any fixed frequency. When active, it occurred with a frequency of less than 15 years, but variability of up to 90 years has occurred during the past 150 years.