Antarctica melting ice, sea levels, water and weather implications
a briefing document
melting ice, sea levels, water and weather implications
is one in a series of briefing documents
investigating the indicators, science, analysis and argument
surrounding global warming.
One of a grouping of documents on global concerns at abelard.org.
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sustainable futures briefing documents
|Tectonics: tectonic plates - floating on the surface of a cauldron|
Recommended, clear article.
[Note that the part of the peninsular (Larsen Shelf) which suffered large shelf losses in recent decades is further north than the rest of Antarctica.]
Worldwide glacier condition is tracked by thirty ‘reference glaciers’ on ‘nine continents’, and many other glaciers. For more details.
mm w.e. means the average number of millimetres of water equivalent (melted snow or ice) lost by the reference glaciers in a year.
The lower the elevation of the glacier’s origin, the more threatened the glacier will be. A glacier terminating at sea level may be fed from much higher elevations. Obviously, similar conditions may apply to glaciers originating in Antartica and in high latitudes. This must be considered when assessing the vulnerability of individual glaciers.
You will note, by the large ranges of some of these numbers reported by varying sources, that a lot of this is rather optimistic guesswork.
more on the melting of glaciers
As already stated, glaciers in general are presently in retreat. It is important to realise that the Greenland and Antarctic ice sheets also produce glaciers, some of them very large.
A glacier is not static, it is a moving river of ice. The speed of that river varies according to several conditions. The illustration above gives a summary of the more important of these conditions. Detailed glaciology is a fairly new science, which is receiving considerable attention due to its great importance. This attention includes a lot of effort trying to understand exactly how the flow of ice works. It is not as easy as it sounds, because exploring deep within ice packs varies from dangerous to impossible.
Thus it is that various instrumentation is under continuous development, from dropping camera probes deep into ice fissures, driving for deep core samples and pinging the ice sheets from satellites, together with much else.
You will find graphs and commentary on recent temperature patterns at medieval warming. I now intend to look at the longer term paleoclimate temperature estimates.
It is useful to remind yourself that temperatures were probably higher for longer in the last interglacial (the Eemian), and that the ice sheets retired further than they have at present. This had the consequence that the seas were higher. But it does look as if we are well on the way to rather accidentally breaking those records.
Notice that in the recent pattern of ice ages, the temperature rises rather rapidly and then starts to steadily peter out. A similar pattern is suggested for the present interglacial as shown in the first of the two graphs linked at medieval warming. In the second graph at medieval warming, can be seen strong hints that this decline pattern has been reversed in the last two hundred years. Of course, the lines do tend to wiggle around according to our estimates, but the trends are certainly suggestive, at least to me. You will also notice, from the table below, that the interglacials have not tended to last for a great percentage of the time during the ‘modern’ period.
Steve McIntyre has done something interesting with the first graph in the “ice age temperature changes” diagram, just above. What he has done is to put an arbitrary line across the graph that roughly estimates the planetary temperature at which Toronto becomes free of ice (he lives in Toronto!). And from this arbitrary line, he estimates the approximate lengths of the interglacials.
What is important to concentrate on is the completely arbitrary nature of the blue line. Had the line instead been linked to Glasgow or even Ottawa, the interglacials would become shorter; or had the line been moved southwards, the interglacials would, of course, become longer.
The definition of an interglacial is a rather arbitrary moving feast, nor does the glaciation extend tidily to a given latitude. It varies according to land and sea conditions, prevailing winds, and even interactions between the heights of the ice sheets. To add to this, the ice sheets advance and retreat according to their mood.
As you can see from the next diagram:
Back beyond the last six hundred thousand years [600kyr], you will see that Toronto would not have had serious glaciation for the previous 2.7 million years; and going even further back, there would also have been no glaciation for Toronto at all.
Thus you will see that this period of glaciation is almost in the nature of a little local difficulty during the history of man, or even of dinosaurs, and I remind you again that here we are talking about Toronto.
Of course, we now have six billion people and growing fast, which we hope to feed. There is also a long-term trend of people moving to the coasts to live and to build vast cities. So interesting as this history is, it won’t be a great comfort if the seas rise by substantial numbers of metres, weather patterns undermine food production and major rivers dry up as glaciers disappear. For example, the Ganges is estimated to be 70% glacial flow during the summer.
The collapse of the West Antarctic would eventually raise world sea levels by around 5 metres, but we’re not all doo-o-o-o-o-o-o-o-m-e-d-d-d yet.
There is a webcam directed towards the Amundsen-Scott South Pole Station (pictured below), with current actual temperature and wind chill.
A virtual tour of McMurdo Station. The tour includes photos of Scott’s hut and much else.
Many links, including “scientific papers, articles, reports, datasets, maps, posters, and information on upcoming events in support of the International Polar Year (IPY)” at lima.usgs.gov.
Thus, an ice shelf is effected by water temperature. The water is quite often frozen right down to the ocean floor. Thus the ice may not be acting as a shelf, but still be in contact with the water at the ice face. Shelved ice is under greater stress and, therefore, can be subject to major break-up.
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