Freethought & Rationalism Archive

ps418 · 04-16-2003, 06:22 AM

Quote:

Originally posted by nermal
GFA--
The nearest library with those references is a bit away. Could you summarize?

Ed

I can't speak for GFA, but I can list the abstracts for some of the papers he cited:

Quote:

The retreat of five small Antarctic Peninsula ice shelves in the late 20th century has been related to regional (possibly anthropogenic) climate warming. We use the record of ice- rafted debris (IRD) in cores to show that the Prince Gustav Channel ice shelf also retreated in mid-Holocene time. Early and late Holocene-age sediments contain IRD derived entirely from local ice drainage basins, which fed the section of ice shelf covering each site. Core- top and mid-Holocene (5�2 ka) sediments include a wider variety of rock types, recording the drift of far-traveled icebergs, which implies seasonally open water at the sites. The period when the Prince Gustav ice shelf was absent corresponds to regional climate warming deduced from other paleoenvironmental records. We infer that the recent decay cannot be viewed as an unequivocal indicator of anthropogenic climate perturbation.

Pudsey, Carol J., Evans, Jeffrey. 2001: First survey of Antarctic sub�ice shelf sediments reveals mid-Holocene ice shelf retreat. Geology: Vol. 29, No. 9, pp. 787�790.

In other words, there was a period of significant ice wastage during the mid-Holocene, 5-2ka. Modern ice wastage therefore need not be an indicator of anthropogenic climate change.

Quote:

We have used ice-flow velocity measurements from synthetic aperture radar to reassess the mass balance of the Ross Ice Streams, West Antarctica. We find strong evidence for ice-sheet growth (+26.8 gigatons per year), in contrast to earlier estimates indicating a mass deficit (20.9 gigatons per year). Average thickening is equal to ~25% of the accumulation rate, with most of this growth occurring on Ice Stream C. Whillans Ice Stream, which was thought to have a significantly negative mass balance, is close to balance, reflecting its continuing slowdown. The overall positive mass balance may signal an end to the Holocene retreat of these ice streams.

Ian Joughin and Slawek Tulaczyk, 2002. Positive Mass Balance of the Ross Ice Streams, West Antarctica. Science 295: 476-480.

The Ross Ice Streams are thickening rather than thinning. However, see the paper by Rignot and Thomas (2002), which points out that the West Antarctic Ice is thinning rapidly to the north and "is probably thinning overall," losing about 65km3/yr, and that the Greenland ice is losing mass of about 50km3/yr.

Eric Rignot and Robert H. Thomas, 2002. Mass Balance of Polar Ice Sheets. Science 297: 1502-1506.

The paper of Zwally et al. (2002) uses satellite data to show that the area of Southern Ocean covered by ice increased by 2-3% from 1979-1998. Note that this does not necessarily imply a positive mass balance. Their abstract:

Quote:

The principal characteristics of the variability of Antarctic sea ice cover as previously described from satellite passive microwave observations are also evident in a systematically calibrated and analyzed data set for 20.2 years (1979�1998). The total Antarctic sea ice extent (concentration >15%) increased by 11,180 � 4190 km2 yr-1 (0.98 � 0.37% (decade)-1). The increase in the area of sea ice within the extent boundary is similar (10,860 � 3720 km2 yr-1 and 1.26 � 0.43% (decade)-1). Regionally, the trends in extent are positive in the Weddel Sea (1.4 � 0.9% (decade)-1), Pacific Ocean (2.0 � 1.4% (decade)-1), and Ross (6.7 � 1.1% (decade)-1) sectors, slightly negative in the Indian Ocean (-1.0 � 1.0% (decade)-1), and strongly negative in the Bellingshausen-Amundsen Seas sector (-9.7 � 1.5% (decade)-1). For the entire ice pack, ice increases occur in all seasons, with the largest increase during fall. On a regional basis the trends differ season to season. During summer and fall the trends are positive or near zero in all sectors except the Bellingshausen-Amundsen Seas sector. During winter and spring the trends are negative or near zero in all sectors except the Ross Sea, which has positive trends in all seasons. Components of interannual variability with periods of about 3�5 years are regionally large but tend to counterbalance each other in the total ice pack. The interannual variability of the annual mean sea ice extent is only 1.6% overall, compared to 6�9% in each of five regional sectors. Analysis of the relation between regional sea ice extents and spatially averaged surface temperatures over the ice pack gives an overall sensitivity between winter ice cover and temperature of -0.7% change in sea ice extent per degree Kelvin. For summer some regional ice extents vary positively with temperature, and others vary negatively. The observed increase in Antarctic sea ice cover is counter to the observed decreases in the Arctic. It is also qualitatively consistent with the counterintuitive prediction of a global atmospheric-ocean model of increasing sea ice around Antarctica with climate warming due to the stabilizing effects of increased snowfall on the Southern Ocean.

Zwally, H.J., Comiso, J.C., Parkinson, C.L. Cavalieri, D.J. and Gloersen, P. 2002. Variability of Antarctic sea ice 1979-1998. Journal of Geophysical Research 107: 10.1029/2000JC000733.

Patrick

God Fearing Atheist · 04-16-2003, 08:32 AM

To finish Patrick's post:

Parkinson uses passive-microwave data from satellites to conclude that "the area of the Southern Ocean experiencing a lengthening of the sea-ice season by at least 1 day per year over the period 1979-99 is 5.6 x 106 km2, whereas the area experiencing a shortening of the sea-ice season by at least 1 day per year is 46% less than that, at 3.0 x 106 km2." The author believes this is a general trend.

Watkins and Simmonds find a statistically significant increase in both sea-ice and sea-ice season between 1987 and 1996.

Yuan and Martinson find that the mean Antarctic sea-ice edge has been expanding at 0.011 degrees latitude a year for the past 18 years.

Long, et al. find the number of icebergs to be increasing, although they pin much of it on advances in observation and tracking.

-GFA

SULPHUR · 04-16-2003, 08:41 AM

Could you you then explain why the Ross ice shelves have been breaking up over the last two years.Both shelf A and B

theyeti · 04-16-2003, 08:54 AM

FWIW, my understanding is that the break-up of the antarctic ice is not considered to be caused by anthropogenic warming. Most climate models put the main effects of that warming in the northren hemisphere, so that the increased temperatures and ice loss in the arctic are probably anthropogenic, but not the antarctic.

theyeti

SULPHUR · 04-16-2003, 09:44 AM

The changes to the temperature of various established ocean currents, especially of the currents to the west of south america and the east of australia in el nino years would indicate a bigger problem in the SH than NH considering the mass of water involved.

ps418 · 04-16-2003, 10:56 AM

Quote:

Originally posted by SULPHUR
Could you you then explain why the Ross ice shelves have been breaking up over the last two years.Both shelf A and B

This can happen even if the net ice mass is increasing. For instance, the rate of ice accumulation inland increases, resulting in faster outward flow of ice to the sea.

Quote:

Though all three of the icebergs are larger than normal, the calving of icebergs is a natural process. Ice shelves form when slow moving glaciers on land flow into the sea. The stiff ice stretches out on the sea as a thick sheet. The more rapidly ice is fed to the shelves, the larger they become. The ice shelf gradually grows thinner farther from shore until cracks within the ice and tidal forces succeed in breaking off pieces, creating icebergs.

source

For instance, Heinrich Events are cooling events associated with expansion of the Laurentide ice sheet in the north hemisphere and are marked by discharge of iceberg armadas into the Atlantic (which left records in the form of ice-rafted debris layers in the ocean sediments).

As I already said, though, Anarctica may be now be losing ice rather than gaining ice, and what we're seeing over the past few years seems to be a fairly major reduction in Anarctic ice shelf.

Patrick

SULPHUR · 04-16-2003, 11:53 AM

Most of what you have said is conjecture whereas the breakdown of the ice shelves is self evident.

ps418 · 04-16-2003, 12:03 PM

Quote:

Originally posted by SULPHUR
Most of what you have said is conjecture whereas the breakdown of the ice shelves is self evident.

Yes, the calving of large antarctic icebergs of the ice shelves is self-evident. But this does not in itself imply that the total volume of Antarctic ice is decreasing, since there is a net accumulation of ice in some areas of Antarctica. As I have already said, though, the most recent evidence suggests that the ice volume is decreasing, which will contribute to sea level rise.

Patrick

ps418 · 04-17-2003, 08:12 AM

Sulpher,

I did a little more searching. I think you'll find the following articles interesting.

Record melt in Arctic and Greenland

Sea-level rise shelved for now

Alaskan glaciers raise sea level

High-water mark: Bleak forecast for sea level in 2100.

SULPHUR · 04-17-2003, 09:58 AM

Thank you .I think we have the kitten on the run. tom

04-16-2003, 08:41 AM	#43
SULPHUR Senior Member Join Date: Nov 2002 Location: hobart,tasmania Posts: 551	ice shelves Could you you then explain why the Ross ice shelves have been breaking up over the last two years.Both shelf A and B

04-16-2003, 09:44 AM	#45
SULPHUR Senior Member Join Date: Nov 2002 Location: hobart,tasmania Posts: 551	ocean currents The changes to the temperature of various established ocean currents, especially of the currents to the west of south america and the east of australia in el nino years would indicate a bigger problem in the SH than NH considering the mass of water involved.

04-16-2003, 11:53 AM	#47
SULPHUR Senior Member Join Date: Nov 2002 Location: hobart,tasmania Posts: 551	ice Most of what you have said is conjecture whereas the breakdown of the ice shelves is self evident.

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04-16-2003, 08:32 AM	#42
God Fearing Atheist Veteran Member Join Date: Sep 2000 Location: Massachusetts, USA -- Let's Go Red Sox! Posts: 1,500	To finish Patrick's post: Parkinson uses passive-microwave data from satellites to conclude that "the area of the Southern Ocean experiencing a lengthening of the sea-ice season by at least 1 day per year over the period 1979-99 is 5.6 x 106 km2, whereas the area experiencing a shortening of the sea-ice season by at least 1 day per year is 46% less than that, at 3.0 x 106 km2." The author believes this is a general trend. Watkins and Simmonds find a statistically significant increase in both sea-ice and sea-ice season between 1987 and 1996. Yuan and Martinson find that the mean Antarctic sea-ice edge has been expanding at 0.011 degrees latitude a year for the past 18 years. Long, et al. find the number of icebergs to be increasing, although they pin much of it on advances in observation and tracking. -GFA

04-16-2003, 08:54 AM	#44
theyeti Veteran Member Join Date: Jun 2001 Location: Denver, CO, USA Posts: 9,747	FWIW, my understanding is that the break-up of the antarctic ice is not considered to be caused by anthropogenic warming. Most climate models put the main effects of that warming in the northren hemisphere, so that the increased temperatures and ice loss in the arctic are probably anthropogenic, but not the antarctic. theyeti

04-17-2003, 08:12 AM	#49
ps418 Veteran Member Join Date: Mar 2001 Location: Louisville, KY, USA Posts: 1,840	Sulpher, I did a little more searching. I think you'll find the following articles interesting. Record melt in Arctic and Greenland Sea-level rise shelved for now Alaskan glaciers raise sea level High-water mark: Bleak forecast for sea level in 2100.

04-17-2003, 09:58 AM	#50
SULPHUR Senior Member Join Date: Nov 2002 Location: hobart,tasmania Posts: 551	Thank you .I think we have the kitten on the run. tom

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