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Global warming = rising water level?

  1. daniel_i_l

    daniel_i_l 866
    Gold Member

    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?
     
  2. jcsd
    Earth sciences news on Phys.org
  3. The ice that might melt and cause a rise in sea levels is sitting on land, in Antarctica and Greenland.
     
  4. 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.
     
    Last edited: Aug 21, 2006
  5. Evo

    Staff: Mentor

    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_level_rise#Glaciers_and_ice_caps
     
    Last edited: Aug 21, 2006
  6. 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.
     
  7. 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

    http://www.washingtonpost.com/wp-dyn/content/article/2006/03/02/AR2006030201712.html

     
  8. 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?
     
  9. GENIERE

    GENIERE 288
    Science Advisor

    …not a recent phenomenon caused by global warming…

     
  10. 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.
     
    Last edited: Aug 22, 2006
  11. I posted this a few months ago somewhere here.
     
  12. 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.
     
    Last edited: Aug 22, 2006
  13. Bystander

    Bystander 3,441
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    "Would happen naturally?" Does happen naturally --- ice flows. It's part of the hydrologic cycle.
     
  14. 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...
     
    Last edited: Aug 22, 2006
  15. 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.
     
  16. Regional warming and regional cooling

    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/2006/08/07/flooding-and-snow-take-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.
     
  17. Bystander

    Bystander 3,441
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    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.
     

  18. It would take much less energy and money than would be required to relocate everyone endangered by the encroaching sea level...
     
  19. 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.
     
  20. Bystander

    Bystander 3,441
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    Do the math --- "why can't we put purple alligators in the sewers" type proposals are wastes of time --- think before asking questions, and you won't be getting answers you deem "sarcastic."
     
  21. Last year in June I saw snow in Somalia. I don't think there are any mountains high enough for that to even happen. The hole pace is desert or arid/semiarid.
     
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