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Apocalypse4Real

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Antarctic Climate Warming
« on: July 21, 2013, 04:34:50 PM »
There is a fairly succinct article in Science News that summarizes current research on warming in the Antarctic, drivers that may influence that warming, and the implications of its warming on global climate.

See: Taking Antarctica's temperature Frozen continent may not be immune to global warming
July 27, 2013; Vol.184 #2
By Erin Wayman

Web edition: July 11, 2013
Print edition: July 27, 2013; Vol.184 #2 (p. 18)

http://www.sciencenews.org/view/feature/id/351507/description/Taking_Antarcticas_temperature

AbruptSLR

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Re: Antarctic Climate Warming
« Reply #1 on: July 21, 2013, 05:23:36 PM »
A4R,

That is a great summary article, and the following article (and attached image) by Steig et al 2013 provides further elaborations about our risks:

Recent climate and ice-sheet changes in West Antarctica compared with the past 2,000 years
by: Eric J. Steig, et al., Nature Geoscience; 6, 372–375; (2013); doi:10.1038/ngeo1778

Abstract
"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 warming4 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 (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."

The attached image focuses on recent WAIS trends are measured by precipitation δ18O; and based on such data I caution that due to the non-linearity of ice mass loss from the WAIS, in the future when the peaks of the natural variability are superimposed on the anthropogenic trend; we can expect a strong increase in ice mass loss from the WAIS in the coming decade (or two) that may be strong enough to push the WAIS ice mass loss past a tipping point.

Caption for the attached figure:

"Fig. S8. Results of a 1-tailed Student’s t-test comparing the decadal-mean for each of the ten members of the ensemble of simulated δ18O in West Antarctic precipitation from the AMIP/coupled experiment for each decade beginning starting in 1865, compared with the 1990’s. As for the observations, the 1990s are distinct from the preceding three decades at moderately high confidence p~0.1, but distinct from the 1940’s and earlier decades only at low confidence. Note that because the quality of the tropical SST data diminishes significantly prior to the latter half of the 20th century, the lack of correspondence between Figs. S4 and Fig. S8 for the late 19th/early 20th century cannot be interpreted as model/data disagreement."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Antarctic Climate Warming
« Reply #2 on: July 24, 2013, 04:35:24 PM »
The quote from the following article states that we also need to be concerned about water loss (probably directly to the atmosphere, or possibly to subglacial basal water; and in either case may some-day contribute to SLR) from the melting of exposed portions of the Antarctic permafrost:

http://science.time.com/2013/07/24/antarctica-melted-in-the-past-and-as-the-climate-warms-its-poised-to-melt-again/

"In another study, researchers from the University of Texas at Austin found that coastal Antarctic permafrost—which, unlike Arctic permafrost, was considered to be stable—is actually melting much faster than scientists had expected. Researchers had though that the permafrost in the region was in equalibrium—ice would melt during the summer, only to refreeze in the winter. But the Texas study, published in Scientific Reports, shows a rapid melting of permafrost in Antarctica’s Garwood Valley, diminishing the overall mass of ground ice. “The big tell here is that ice is vanishing—it’s melting faster each time we measure,” said Joseph Levy, a research associate at the University of Texas’s Institute for Geophysics and the lead author on the paper.
“That’s a dramatic shift from recent history.”
It’s important to note that global warming is not responsible for the permafrost melt here—that region of Antarctic actually experienced a cooling trend from 1986 to 2000, followed by relatively stable temperatures. The Scientific Letters researchers suggest instead that the melting is due to an increase in radiation from sunlight resulting from changing weather patterns that allow more light to reach the ground during the summer. (In the winter, of course, Antarctica experiences 24-hour darkness.) As the permafrost melts, it actually alters the land surface, creating “retrogressive thaw slumps.” The changes observed in the study are occurring around 10 times faster than the average during the Holocene, the current geological epoch, and can actually be seen with time-lapse photography:  Climate models expect Antarctica to warm in the decades to come, which means melting and land change are likely to accelerate."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson