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?
Farsight said: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.Farsight said:The ice that might melt and cause a rise in sea levels is sitting on land, in Antarctica and Greenland.
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.daniel_i_l said: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?
There is no doubt anymore that the ice is melting in Antartica and Greenland.Farsight said:The ice that might melt and cause a rise in sea levels is sitting on land, in Antarctica and Greenland.
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.
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.
…not a recent phenomenon caused by global warming…Skyhunter said:…There is no doubt anymore that the ice is melting in Antartica and Greenland…
“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
mhalavo said: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?
Mk said: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.
Andre said: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.
mhalavo said: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.
Bystander said:"Would happen naturally?" Does happen naturally --- ice flows. It's part of the hydrologic cycle.
mhalavo said: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 said: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.
Bystander said: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 said: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.
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.nannoh said: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.
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.
Unless it happened too slow to really notice anything.mhalavo said:It would take much less energy and money than would be required to relocate everyone endangered by the encroaching sea level...
It would be far cheaper, as well as more feasible, to build levees like the ones in Holland, than to relocate cities or to try pumping sea water to the center of Antarctica.mhalavo said: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.
Or is it?GENIERE said:…not a recent phenomenon caused by global warming…
http://www.breitbart.com/news/2006/08/21/060821191826.o0mynclv.html [Broken]The shrinking of the glaciers since the 19th century is "the result of the atmosphere's natural warming, following volcanic eruptions for example and greenhouse gases, created by human activities, which have aggravated the situation further," he said.
Mk said: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.
Except Antartica is already warming. At least according to the http://www.antarctica.ac.uk/Key_Topics/IceSheet_SeaLevel/index.html.Andre said: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.
Over the past 50 years, the west coast of the Peninsula has been one of the most rapidly-warming parts of the planet, with annual mean temperatures rising by nearly 3°C and the largest warming occurring in the winter season. This is approximately 10 times the mean rate of global warming, as reported by the Intergovernmental Panel on Climate Change (IPCC). Upper ocean temperatures to the west of the Peninsula have also increased by over 1°C since 19554. The east coast of the Peninsula has warmed more slowly and here the largest warming has taken place in summer and autumn.
Analysis of weather balloon data collected over the past 30 years has shown that the Antarctic atmosphere has warmed below 8 km and cooled above this height. This pattern of warming in the troposphere and cooling in the stratosphere is seen globally and is the expected signature of increases in greenhouse gasses, such as carbon dioxide. However, the 30-year warming at 5 km over the Antarctic during winter (0.75°C) is over three times the average rate of warming at this level for the globe as a whole.
Despite very low rates of snowfall and low ice-flow rates, the huge area of the East Antarctic ice sheet means that even tiny changes in the thickness in this region could have a substantial effect on sea level rise. Recent evidence from satellite altimeters suggests that over the last decade there has been a thickening of a couple of centimetres per year and a little more in some limited regions. Debate concerning the exact distribution and magnitude of this change continue. It is possible that this observation represents the emergence of a long-predicted consequence of anthropogenic climate change, that the rate of snow-fall over Antarctica will increase, and act to slow the rate of sea level rise. However, even if this is the case, and if climate change continues in future, current climate models predict that the increase in snowfall over East Antarctica could only marginally reduce the rate of global sea level rise