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Antarctica, satellite photo from 2005, with various
data added. Original image credit: NASA/JPL
65°S is the equivalent distance from the South Pole as Iceland is from
the North Pole.
Recommended, clear article.
“A team of NASA and university scientists has found clear evidence
that extensive areas of snow melted in west Antarctica in January 2005
in response to warm temperatures. This was the first widespread Antarctic
melting ever detected with NASA's QuikScat satellite and the most significant
melt observed using satellites during the past three decades. Combined,
the affected regions encompassed an area as big as California.
“The observed melting occurred in multiple distinct regions,
including far inland, at high latitudes and at high elevations, where
melt had been considered unlikely [...]”
—
“Antarctica has shown little to no warming in the recent past
with the exception of the Antarctic Peninsula [...]
[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.]
“Changes in the ice mass of Antarctica, Earth's largest freshwater
reservoir, are important to understanding global sea level rise. Large
amounts of Antarctic freshwater flowing into the ocean also could affect
ocean salinity, currents and global climate.”
| continent / country |
area in square kilometres |
| Antartica |
14,000,000 |
| Russia |
17,075,200 |
| Canada |
9,984,670 |
| USA |
9,826,630 |
| China |
9,596,960 |
| Brazil |
8,511,965 |
| Australia |
7,686,850 |
the melting of glaciers
diagram showing glacial ice evolution
- melting and slipping away from the bedrock
interactive image: hover with
your mouse, clickable areas change to a hand icon
- The ablation zone is where there is an overall
loss of glacial material, as the amount of ice melting in Spring and
Summer exceeds the amount of Winter snow deposits. The accumulation
zone is where snow fall exceeds melting. A balance zone is deemed between
these two.
Although presently, there is a widespread recession of glaciers, be
aware that a glacier is a dynamic system that may be advancing one year,
and receeding another. Thus, the position of these zones will alter.
- A warmer planet is expected to be a dustier planet. Vast quantities
of dust
from erosion and desertification are already being shifted around the
planet. If this dust lands on the ice fields, it will reduce albedo.
Of course, as the ice fields shrink, the albedo of the earth steadily
reduces, adding yet another positive feedback
- As the ice tongue (the leading edge of the glacier, on the above diagram
protruding into the sea) erodes, it has a partial effect of taking a
stopper out of a bottle. This allows the glacier to flow more freely.
The faster the glacier flows, the more friction heats up the underside
of the glacier. As it becomes liquid, that liquid lubricates the glacier,
allowing it to flow still more quickly.
- A glacier thinning results in lower downward pressure. Downward pressure
can have two effects, depending upon the conditions:
- helping to anchor the glacier to the rock substrate;
- causing heating, and thus melting.
- Glacier thinning lowers the elevation of ice, and lower elevations
are warmer.
The pressure of large masses of ice also depresses land elevation slightly,
so there is some bounce-back as the ice fields melt.
- On mountain glaciers, a common phenomenon is the undercutting of the
rock walls at the sides of the glacier. This causes rock to fall onto
the ice, and carves out the great U-valleys that someone probably taught
you about in school. These rock falls also change the albedo of the
ice surface.
interesting ‘facts’
about Antarctica
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.
- Only five percent of the Antarctica coastline is ice-free.
- Probably fewer than a hundred thousand people have ever visited Antarctica.
- Antarctica has thirty million cubic kilometres of ice. If this ice
melted, the global sea level would rise by an estimated 56 to 80 metres.
The Greenland ice sheet is estimated to be capable of rising sea levels
by 6 to 7 metres. These ice sheets are estimated to contain about 70
to 90% of the world’s fresh water, 10% of that being in the Greenland
ice sheet.
70% of the Earth’s surface is covered with water. In total, there
is about 1½ billion cubic metres of water on the Earth. 97% of
that water is sea water (so only 3% is fresh water).
Satellite measurements of changes in sea levels are presently of the
orders of small numbers of millimetres. Measuring and standardising
such small differences is very difficult and must be treated with caution.The
depth of the seas varies from place to place on the planet by virtue
of gravity variations, thermal expansion, changing tides and the land
rising and sinking (including that under the sea). Meanwhile, the height
of the satellite must be measured against this varying background!
- The Antarctic forms a
huge heat sink, effecting much of the world’s weather systems.
- The land area of Antarctica is about fifty-eight times that of the
British Isles.
- Greenland and the west Antarctic ice sheets are widely grounded below
sea level. As the ice sheets thin, the lowered weight decreases their
grip on the land. As the ice shelves recede, the warming water can erode
the ice sheet into an ice shelf, and thus the
process advances.
- Several processes are combining in positive feedbacks
to increase the rate of melting of the ice sheets and glaciers.
- Due to the high albedo
of the ice sheets, they act as air-conditioning for the planet, as well
as there being many communities that are dependent on glaciation to
maintain a flow of fresh water during the summer season. There is widespread
recession of the majority of glaciers around the world.
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 below 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.
past ice ages
and interglacials
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
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.
|
Start (kyr) |
End (kyr) |
Length(kyr) |
| Holocene |
12.3 |
|
12.3+ |
| Eemian |
130 |
114 |
16 |
| 240 kyr |
244 |
240 |
4 |
| 330 kyr |
337 |
325 |
12 |
| Stage 11 |
418 |
395 |
23 |
| [kyr = 1,000 years] |
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 four hundred thousand years [400kyr], you will see
that Toronto would not have had an interglacial for the previous 2.7 million
years; whereas going even further back, there would have been no serious
glacials for Toronto at all.
See The
geological timeline for further information on Pal (Palocene), Eo
(Eocene) etc.
Recall that on these timescales, planetary climate is also affected by
tectonic plate movement.
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.
“Over 2 million people in the La Paz region depend heavily on
the thawing of Chacaltaya and neighboring glaciers for tap water and,
indirectly, for electricity supplies.
“ "At least 35 percent of the drinking water comes from
melting glaciers, and about 40 percent of the electricity," said
Oscar Paz, the head of the Bolivian Climate Change Panel, a government
task force.”
—
“Ecuador's capital Quito, with 1.5 million people, and the Peruvian
capital Lima, with 8 million people, also rely on melting glaciers for
water and energy supplies.” [Quoted from planetark.org]
related material
pressure on water
resources
giant ice shelf
broke free in the arctic
glossary
- ice shelf:
- floats on the sea/ocean;
- ice sheet:
- situated on land.
- 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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