Global warming = rising water level?


by daniel_i_l
Tags: global, rising, warming, water
daniel_i_l
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#1
Aug21-06, 10:21 AM
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If you have ice cubes in a glass of water and they melt the level of the water goes down. Why are glaciers in the ocean different?
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Farsight
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Aug21-06, 10:45 AM
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The ice that might melt and cause a rise in sea levels is sitting on land, in Antarctica and Greenland.
rbj
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Aug21-06, 11:56 AM
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Quote Quote by Farsight
The ice that might melt and cause a rise in sea levels is sitting on land, in Antarctica and Greenland.
in fact, there is enough ice on Greenland to raise ocean levels 7 meters if it all melted and on Antarctica to raise the oceans 60 meters (if i recall correctly) if it all melted. (that would change the coastal map worldwide quite considerably.)

the scary thing is that this is a positive-feedback mechanism. since polar ice reflects sunlight better than brown dirt or gray rock, the warmer the earth gets, the more of this ice covering ground is melted, the more of this ground is exposed, the more sunlight is absorbed instead of reflected, and the more conditions are changed to enable warming at an even faster rate. if this becomes a "runaway train" that gets away from us (out of control), we could start an avalanche mechanism that our descendants just cannot stop and there is enough stored water "in the bank" that the oceans could rise seemingly indefinitely.

the oceans did rise 1/5 meter in the 20th century and is expected to rise 1 meter in the 21st century. since all of the change agents (human population, carbon consumption, and CO2 levels over the post-ice-age baseline of 275 ppm) are increasing exponentially, if this sea level rise continues exponentially, it could go up 5 meters in the 22nd, perhaps 25 meters in the 23rd century. it's a long way off, but we might be sowing seeds for such a calamity now that our descendants will have a b1tch of a time reversing. it's all because of a life-style of consumption and that fossil fuels were priced so cheaply at the expense of our descendants. in economics, this is called "externalities": when some group of people gets to have a party while another group of people, neither consenting to it nor benefitting from it, get to pay for the party. i'm sure our descendants will be thankful.

we (the human race) better watch out. we could be starting a very slow, but unstoppable, avalanche of global warming.

Evo
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Aug21-06, 01:09 PM
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Global warming = rising water level?


Quote Quote by Farsight
The ice that might melt and cause a rise in sea levels is sitting on land, in Antarctica and Greenland.
Actually a lot of the ice is not over land. The ice that is over land, Greenland and the Antartic would take a very long time to melt.

To answer the OP's question, Ice shelves that float in the ocean would not affect sea levels if they melted.

"Glaciers and ice caps

Each year about 8 mm (0.3 inches) of water from the entire surface of the oceans goes into the Antarctica and Greenland ice sheets as snowfall. If no ice returned to the oceans, sea level would drop 8 mm every year. Although approximately the same amount of water returns to the ocean in icebergs and from ice melting at the edges, scientists do not know which is greater — the ice going in or the ice coming out. The difference between the ice input and output is called the mass balance and is important because it causes changes in global sea level.

Ice Shelves float on the surface of the sea and, if they melt, to first order they do not change sea level. Likewise, the melting of the northern polar ice cap which is composed of floating pack ice would not significantly contribute to rising sea levels. Because they are fresh, however, their melting would cause a very small increase in sea levels, so small that it is generally neglected. It can however be argued that if ice shelves melt it is a precursor to the melting of ice sheets on Greenland and Antarctica.

Scientists lack knowledge of changes in terrestrial storage of water. Between 1910 and 1990, such changes may have contributed from –1.1 to +0.4 mm/yr.

If all glaciers and ice caps melt, the projected rise in sea level will be around 0.5 m. If the melting includes the Greenland and Antarctic ice sheets (both of which contain ice above sea level), then the rise is a more drastic 68.8 m. [3]

The snowline altitude is the altitude of the lowest elevation interval in which minimum annual snow cover exceeds 50%. This ranges from about 5,500 metres above sea-level at the equator down to sea-level at about 70 degrees N&S latitude, depending on regional temperature amelioration effects. Permafrost then appears at sea-level and extends deeper below sea-level pole-wards.

As most of the Greenland and Antarctic ice sheets lie above the snowline and/or base of the permafrost zone, they cannot melt in a timeframe much less than several millennia; therefore it is likely that they will not contribute significantly to sea-level rise in the coming century. They can however do so through acceleration in flow and enhanced iceberg calving.

Climate changes during the 20th century are estimated from modelling studies to have led to contributions of between –0.2 and 0.0 mm/yr from Antarctica (the results of increasing precipitation) and 0.0 to 0.1 mm/yr from Greenland (from changes in both precipitation and runoff).

Estimates suggest that Greenland and Antarctica have contributed 0.0 to 0.5 mm/yr over the 20th century as a result of long-term adjustment to the end of the last ice age.

I use the wiki reference below because it captures a lot of data on one page.

http://en.wikipedia.org/wiki/Sea_lev...s_and_ice_caps
Skyhunter
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#5
Aug21-06, 01:58 PM
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Quote Quote by daniel_i_l
If you have ice cubes in a glass of water and they melt the level of the water goes down. Why are glaciers in the ocean different?
The level does not go down, it remains constant. The reason being that the floating ice has already displaced its weight in unfrozen water. If the level goes down in a glass it is because the ice is being held under water by friction against the sides of the glass.
Skyhunter
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#6
Aug21-06, 02:08 PM
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Quote Quote by Farsight
The ice that might melt and cause a rise in sea levels is sitting on land, in Antarctica and Greenland.
There is no doubt anymore that the ice is melting in Antartica and Greenland.

http://news.bbc.co.uk/1/hi/world/europe/3922579.stm

In 2001 NASA scientists published a major study based on observations by satellite and aircraft.

It concluded that the margins of the Greenland ice-sheet were dropping in height at a rate of roughly one metre a year.

Now, amid some of the most hostile conditions anywhere on the planet, Carl Boggild and his team have recorded falls as dramatic as 10 metres a year - in places the ice is dropping at a rate of one metre a month.
http://www.washingtonpost.com/wp-dyn...030201712.html

The new Antarctic measurements, using data from two NASA satellites called the Gravity Recovery and Climate Experiment (GRACE), found that the amount of water pouring annually from the ice sheet into the ocean -- equivalent to the amount of water the United States uses in three months -- is causing global sea level to rise by 0.4 millimeters a year. The continent holds 90 percent of the world's ice, and the disappearance of even its smaller West Antarctic ice sheet could raise worldwide sea levels by an estimated 20 feet.
mhalavo
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Aug21-06, 03:01 PM
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What's the plausibility of just pumping and storing water onto a portion of Antarctica that never gets to be above freezing? That has to be cheaper and more feasible than relocating all of the cities near the ocean. Has anyone seen a proposal to do anything like this?
GENIERE
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#8
Aug21-06, 09:43 PM
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Quote Quote by Skyhunter
…There is no doubt anymore that the ice is melting in Antartica and Greenland…
…not a recent phenomenon caused by global warming…

“Greenland's glaciers have been shrinking for the past century, according to a Danish study, suggesting that the ice melt is not a recent phenomenon caused by global warming

http://www.breitbart.com/news/2006/0....o0mynclv.html
Andre
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#9
Aug22-06, 09:11 AM
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Quote Quote by mhalavo
What's the plausibility of just pumping and storing water onto a portion of Antarctica that never gets to be above freezing? That has to be cheaper and more feasible than relocating all of the cities near the ocean. Has anyone seen a proposal to do anything like this?
I'm afraid that it's not feasible. Ice sheets are dynamic and do flow. Increasing the height of the ice sheet will cause increased outflow sideways and the ice gets back into the sea eventually.

Anyway, the observations of Grace are consistent with Antarctic cooling. The amount of precipitation on the summit of Antarctica is shown to be rather strongly correlated with temperature according to the work of Michel Helsen including his PhD thesis on his site. Consequently, when it's colder, the snow accumulation decreases but the outflow sideways does not react immediately due to inertia.

So we have to wait until Antarctica warms too, then the accumulation will pick up again, lowering the sea levels.
Mk
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#10
Aug22-06, 12:50 PM
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I posted this a few months ago somewhere here.
Quote Quote by Mk
As the news media often does, highly complicated matters are over-simplified to give viewers and readers easy-to-digest meals that do not require much thinking—this is where the problem inlies in understanding of sea level.
Mean sea level (MSL) is the average (mean) height of the sea, with reference to a suitable reference surface. Defining the reference level (Permanent Service for Mean Sea Level), however, involves complex measurement, and accurately determining MSL can prove difficult. Finding the MSL change involves comparing the local height of the mean sea surface with a "level" reference surface or datum, called the geoid. In a state of rest with absence of external forces (totally stagnant water), the mean sea level would be the same at every point on the Earth. The geoid would only deviate from the perfect sphere in this theoretical model with local differences in MSL from local deviations in the Earth's gravitational field. In reality, due to currents, air pressure variations, temperature variations, salinity variations, etc., this does not occur, and prevents certain verifiable long term averages from being calculated. The location-dependent, but persistent in time, separation between mean sea level and the geoid is referred to as "stationary sea surface topography," which varies globally by ±2 meters, further offsetting the MSL.

Traditionally, one must have had to process sea-level measurements to take into account the effect of the 228-month Metonic cycle and the 223-month eclipse cycle on the tides (both having to do with the moon's effect on sea level). MSL never remains constant over the surface of the entire earth. For instance, MSL at the Pacific end of the Panama Canal stands approximately 20 centimeters (0.6 ft) higher than at the Atlantic end.

Despite the difficulties, aviators flying under instrument flight rules (IFR) must have accurate and reliable measurements of their altitudes above (or below, for airports such as in the Netherlands) local MSL, and the altitude of the airports where they intend to land.

Several terms are used to describe the changing relationships between sea level and dry land. When the term "relative" is used, it connotes change that is not attributed to any specific cause. The term "eustatic" refers to changes in the amount of water in the oceans, usually due to climatic changes. The melting of glaciers at the end of ice ages is an example of eustatic sea level rise. The term "isostatic" refers to changes in the land level, of land masses due to thermal buoyancy or tectonic effects and implies no real change in the amount of water in the oceans, although isostatic changes change the MSL because it is relative to the land. The subsidence of land due to the withdrawal of groundwater is an isostatic cause of relative sea level rise. Paleoclimatologists can track sea level by examining the rocks deposited along coasts that are very tectonically stable, like the east coast of North America. Areas like volcanic islands often experience relative sea level rise as a result of isostatic cooling of the rock which causes the land to sink.
mhalavo
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#11
Aug22-06, 01:45 PM
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Quote Quote by Andre
I'm afraid that it's not feasible. Ice sheets are dynamic and do flow. Increasing the height of the ice sheet will cause increased outflow sideways and the ice gets back into the sea eventually.
Isn't that what would happen naturally anyway if precipitation begins to accelerate on Antarctica? Couldn't it buy us as much time as if nature deposited the snow there... until "whatever" occurs that will send us into the next ice age.
Bystander
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Aug22-06, 01:52 PM
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Quote Quote by mhalavo
Isn't that what would happen naturally anyway if precipitation begins to accelerate on Antarctica? Buying us as much time as if nature deposited the snow there... until "whatever" occurs that will send us into the next ice age.
"Would happen naturally?" Does happen naturally --- ice flows. It's part of the hydrologic cycle.
mhalavo
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Aug22-06, 01:57 PM
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Quote Quote by Bystander
"Would happen naturally?" Does happen naturally --- ice flows. It's part of the hydrologic cycle.
I understand it happens naturally. I was just questioning why ice/snow placed there by man would suffer a fate different than if it was placed there naturally.

i.e. it could buy us many, many years...
Andre
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Aug22-06, 02:22 PM
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Anyway, even if the sea level rise would persist, it still may be not feasible. Any idea what 1 mm eustatic sea level rise would require for energy to be spend to transport it to central Antarctica from sea level to three kilometers elevation over a distance of a few thousand kilometers. And expect it to be ice after a few hours at -60C.
nannoh
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Aug22-06, 02:48 PM
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Snow in South Africa. Last time this happened was 25 years ago only an inch or so. This time its more like a few feet.

http://theworldnow.wordpress.com/200...-south-africa/

Is it possible that North Americans are egocentric enough to view "global climate" as pertaining only to those areas that influence North American markets, citizens and industry? Meanwhile the "globe" that is our planet maintains a balance of temperature and weather through microclimates and regional shifts in weather patterns.
Bystander
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Aug22-06, 03:24 PM
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Quote Quote by mhalavo
I understand it happens naturally. I was just questioning why ice/snow placed there by man would suffer a fate different than if it was placed there naturally.

i.e. it could buy us many, many years...
You wanta pump 10,000 tons of sea water per second a km in the air at a minimum energy expenditure rate of 100 GW (total power for U. S.) to prove that ice flows off continental margins at a rate proportional to its deposition rate, go for it --- it's an expensive experiment given that no one knows what the "natural" rate of sea level rise is at the moment (we're only 12-15 ka out of the last ice age, and sea level is still recovering from that), and given the Corps of Engineers experience with controlling beach erosion, and given that it ain't all that likely to work as far as stabilizing sea level at some arbitrarily decided point.
mhalavo
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#17
Aug22-06, 03:30 PM
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Quote Quote by Andre
Anyway, even if the sea level rise would persist, it still may be not feasible. Any idea what 1 mm eustatic sea level rise would require for energy to be spend to transport it to central Antarctica from sea level to three kilometers elevation over a distance of a few thousand kilometers. And expect it to be ice after a few hours at -60C.

It would take much less energy and money than would be required to relocate everyone endangered by the encroaching sea level...
mhalavo
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Aug22-06, 03:36 PM
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Quote Quote by Bystander
You wanta pump 10,000 tons of sea water per second a km in the air at a minimum energy expenditure rate of 100 GW (total power for U. S.) to prove that ice flows off continental margins at a rate proportional to its deposition rate, go for it --- it's an expensive experiment given that no one knows what the "natural" rate of sea level rise is at the moment (we're only 12-15 ka out of the last ice age, and sea level is still recovering from that), and given the Corps of Engineers experience with controlling beach erosion, and given that it ain't all that likely to work as far as stabilizing sea level at some arbitrarily decided point.
If we had a pump that could keep up with the sarcasm you're putting out we could use that... I just posed a question about a possible engineering solution to a possible future problem.


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