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Antarctica (Ice Shelves) -- Summary
If global mean sea level is ever to rise significantly, earth's polar regions will have to warm considerably; and in Antarctica, which is the coldest land on earth, the effects of that warming would be expected to be manifest first and foremost along its coasts, which represent the continent's furthest extensions from the South Pole and are the places where great ice shelves are found.  So what has happened there of late?  Is this region truly the "canary in the coal mine" so many climate alarmists claim it to be, i.e., the place where CO2-induced global warming will express itself most fiercely and obviously, leading to the disintegration of the continent's huge ice shelves?

In some places along the coasts of Antarctica, such as the Antarctic Peninsula, there has indeed been a significant localized warming over the past several decades that actually has resulted in the destruction of some ice shelves.  Pudsey and Evans (2001), for example, report that five small ice shelves connected to the Peninsula have been retreating throughout the entire period of historical observation, i.e., since about 1843, and that this retreat intensified in the late 1980s, leading to the breakout of two of the ice shelves (Larsen-A and Prince Gustav Channel) in 1995.  However, they caution that "we should not view the recent decay as an unequivocal indicator of anthropogenic climate change," because their study of ice-rafted debris found in sediment cores extracted from the Prince Gustav Channel indicates that the ice shelf also retreated during the mid-Holocene, without any help from elevated atmospheric CO2 concentrations, and that it did not reform until sometime after 1900 years ago, i.e., after the demise of the Roman Warm Period, which interval of relative warmth (again without the benefit of high atmospheric CO2 concentrations) must have been warmer than it is now globally, for the current warmth of the Antarctic Peninsula is generally regarded as being a regional anomaly.

Much the same conclusion was reached by Vaughan et al. (2001), who in reporting the results of their study of the Antarctic Peninsula and Bellingshausen Sea note that "rapid regional warming has led to the loss of seven ice shelves during the past 50 years."  Nevertheless, they too say sediment cores reveal that from 6000 to 1900 years ago, the Prince Gustav Channel Ice Shelf "was absent and climate was as warm as it has been recently," which once again suggests that the modern anomalous warmth of this region of the globe did not achieve a level commensurate with that of the Roman Warm Period until the mid-1990s.

With respect to the ice shelf extension of the primary body of the West Antarctic Ice Sheet, Bindschadler (1998) reports that both its grounding line and ice front have been retreating for several decades, but that its ice front "now appears to be nearly stable," which situation is resulting in an actual expansion of the Ross Ice Shelf and a slowing of the overall retreat of the ice sheet.

In East Antarctica, Kim et al. (2001) measured positions of ice shelf margins along the coast of Queen Maud Land from 1963 satellite reconnaissance photography and 1997 RADARSAT synthetic aperture radar images for comparison with coastlines inferred by other researchers who used Landsat data from the mid-1970s."  Over the 34-year period from 1963 to 1997, the ice shelves they studied lost about 6.8% of their total area.  However, most of this reduction occurred over the 12-year period from 1963 to 1975.  Over the following 22-year period stretching from 1975 to 1997, they found that "ice margin positions have stabilized or even readvanced."  They also say that "on the basis of the measured mean annual temperatures at coastal stations, extrapolated measured temperature trends, and the taking of a mean annual temperature of -5C as a stability criterion, we predict that these ice shelves will remain stable for several hundred years."

In another East Antarctic study, Hemer and Harris (2003) extracted and analyzed a sediment core from beneath the Amery Ice Shelf at a point that is currently about 80 km landward of the location of its present edge.  This core contained a 0.5-m-thick surface layer of siliceous mud and diatom ooze of marine origin, wherein they discovered "peaks in biogenic opal, ADA [absolute diatom abundance], and Fragilariopsis curta," which peaks are said by them to be "associated with increased proximity to an area of primary production, such as the sea-ice zone."  Quoting them further, "the relative abundance of F. curta begins to increase ca. 5700 14C yr B.P. [before present] toward the peak in F. curta abundance and ADA observed ca 750 14C yr B.P.," which trend they attribute "to a gradual retreat of the ice front, thus bringing the productive sea-ice zone waters closer to the [core] site over the period from 5700 14C yr B.P. to ca. 750 14C yr B.P."

In commenting on these observations, Hemer and Harris say their analysis suggests a prior Holocene retreat of the Amery Ice Shelf to "at least 80 km landward of its present location."  This observation, in turn, suggests that since the cessation of the ice shelf's retreat some 750 14C yr B.P., there has been a major seaward extension of the ice shelf's edge, possibly driven by the cooling associated with the development of the Little Ice Age, which in turn suggests that we could again witness some retreat of the ice shelf's edge if the Modern Warm Period ever begins to manifest itself in East Antarctica, which it has yet to do.  It also suggests that if this does occur, we need not be unduly concerned; for the Amery Ice Shelf has retreated before, peaking during either the Roman or Medieval Warm Periods (or both), when air temperatures must have been higher than they are now, all without any catastrophic increase in sea level.

In summary, these several observations reveal that (1) there has been a localized warming-induced destruction of small ice shelves on the Antarctic Peninsula over the past few decades, although that warming has not taken temperatures back to levels characteristic of the Roman Warm Period, when atmospheric CO2 concentrations were much lower than those of today, (2) the ice front of the West Antarctic's Ross Ice Shelf was in retreat for several decades, but it is now nearly stable, (3) the ice front of the Amery Ice Shelf of East Antarctica was at least 80 km closer to the continent prior to the globe's descent into the Little Ice Age, implying greater warmth during the Roman and Medieval Warm Periods than that experienced in modern times, and (4) ice shelf margins along the coast of East Antarctica's Queen Maud Land retreated from 1963 to 1975, but they have subsequently stabilized or even readvanced a bit.  None of these observations provide any support for the proposition that CO2-induced global warming of either the past century or quarter-century is having any effect at all on Antarctic ice shelves, or, for that matter, that there has even been any CO2-induced global warming during the 20th century.  In fact, these observations tend to suggest just the opposite.

References
Bindschadler, R.  1998.  Future of the West Antarctic Ice Sheet.  Science 282: 428-429.

Hemer, M.A. and Harris, P.T.  2003.  Sediment core from beneath the Amery Ice Shelf, East Antarctica, suggests mid-Holocene ice-shelf retreat.  Geology 31: 127-130.

Kim, K.T., Jezek, K.C. and Sohn, H.G.  2001.  Ice shelf advance and retreat rates along the coast of Queen Maud Land, Antarctica.  Journal of Geophysical Research 106: 7097-7106.

Pudsey, C.J. and Evans, J.  2001.  First survey of Antarctic sub-ice shelf sediments reveals mid-Holocene ice shelf retreat.  Geology 29: 787-790.

Vaughan, D.G., Marshall, G.J., Connolley, W.M., King, J.C. and Mulvaney, R.  2001.  Devil in the detail.  Science 293: 177-179.