Introduction There is much talk of a possible imminent collapse of the ice sheets of Greenland and Antarctica due to global warming that would be caused by man, and catastrophic sea level rise would happen.
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Recently my attention was drawn to the study by Alan Carlin (2007), which was basically about how the emission reduction could be a dangerous strategy to avoid climate change. Carlin sounds the alarm about climate change saying, "The ancient and long-standing concern about climate change is that there could be a 'tipping point' where a continuous rise in global temperatures warming could trigger a self-reinforcing, non-linear , or other hazardous environmental effects beyond those resulting immediately the same temperature increase. "
Carlin argues that the collapse of large ice sheets is one of the greatest threats we face. Basa his discussion of this perceived threat in studies of Hansen (2007) and others who propose that the rapid melting of ice sheets in Greenland and West Antarctica (and thus the entire Antarctic) lead to a sea level rise of five meters or more. Carlin notes that, "Hansen et al believe that the most critical of these harmful effects is the possibility of substantial sea level rise due to the breakage of parts or all of the ice cover of Greenland or West Antarctica."
Hansen's scenario is not reasonable. By the way, is not even possible. Hansen's apparent ignorance of the mechanism by which glaciers flow leads to huge errors. In this study, we describe the dynamics of glaciers, such as the balance of the glacier, how glaciers flow (through a process known as "creep" (or "crawled very slow"), as the "creep" is related to temperature, pressure and stress, and how the simple rules of crept us understand some observations on glaciers.
Glacier Model Hansen is wrong!
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Hansen is a modeller, and collapse scenario of the ice sheets is based on a false model.
Their model has a layer of ice sliding along an inclined plane, lubricated by meltwater from the surface, which increases global warming. The same model is adopted in many models copied from older ones. Christofferson and Hambrey (2006) and Lambert et al, (2207) are typical examples. A popular article based on the same flawed model appeared in the June 2007 issue of National Geographic and the idea is present in textbooks as 'The Great Ice Age' (2000) by RCL Wilson et al.
Unfortunately, Hansen's model does not include the main form of the ice sheets of Greenland or Antarctica, no understanding of how glaciers flow. The predicted behavior of ice sheets is based on melting and accumulation rates of today, and the concept of an ice sheet sliding down an inclined plane on a base lubricated by meltwater, which itself be growing because of global warming. The idea of \u200b\u200ba glacier sliding downhill on a base lubricated seemed like a good idea when it was first presented by de Saussure in 1779, but since then he has learned a lot more.
is not enough to think that the current climate in coming decades may affect the flujote ice sheets. Ice sheets do not simply grow and melt in response to global temperature. Anyone with this naïve view would have difficulty explaining why the ice was present in the Southern Hemisphere for 30 million years, and in the northern hemisphere for only 3 million.
To understand what is possible, it is necessary to know something about the physics of glacier flow, which explains some things that are not taken into account in the Hansen model, such as:
- Why crystals at the foot of the glacier ice is a thousand times larger than the snow that feeds them?
- Why the lake ice deforms at lower voltages than other ice? Why
- cracks only extend to a depth limit?
Actually, the ice sheets of Greenland and Antarctica are located in basins concave and can not slip out of them along a plane. In addition, the flow of glaciers depends on the tensions as well as temperatures, and most of the ice sheets are well below the melting point. The accumulation of miles of undisturbed ice in ice cores from Antarctica and Greenland (the ones that are sometimes used to feed ideas on global warming) are hundreds of thousands of years of accumulation with no melting or flow. Except around the edges, ice sheets flow into the base and depend on geothermal heat, no heat on the surface climate. It is impossible that the ice sheets of Antarctica or Greenland "collapse."
balance of a glacier
In general, the glaciers grow, flow, and melt steadily, with a balance of gains and losses . Snow falls on high ground. It is becoming more compact with time, the air is expelled, and becomes solid ice. Some air bubbles are trapped, and can be used by scientists to examine later the composition of air at the time of deposition. More snowfall form another layer on top, which follows the same process, so the ice grows in thickness by adding new layers of snow on the surface. The existence of such layers, youngest above, allows the glacial ice is studied over time, as in the Vostok ice core, a primary source of data on temperature and CO2 over 400,000 years.
When the ice is thick enough, it begins to flow under the impetus of gravity. A mountain glacier flows downhill, but in some parts can flow uphill emulated by a larger mass of ice. In an ice flow occurs from the center top of the stool toward the edges of the ice. When the ice reaches a lower altitude or a lower latitude, where the temperature is higher, it begins to melt or evaporate.
(Evaporation and melting simultaneously is called 'ablation', but for simplicity I use the term 'melting by now.)
If growth and melting balance, the glacier seems to be' steady '. If rainfall exceeds the melting, the glacier grows. If melting exceeds precipitation the glacier recedes. How
glaciers move
The flow is primarily through a process called "creep" (or "crawl slowly '), essentially the movement of atoms from one crystal to another. The first clues to this came from a study of lake ice, which can flow at voltages well below the shear stress or cut, if the stress is applied parallel to the surface of the lake. This is a consequence of ice crystal properties. Ice is a hexagonal mineral with glide planes parallel to the base. (See [a] in Figure 1). The lake ice is a sheet of crystals with vertical c-axes and glide planes all parallel to the lake surface, so that a push to the glide planes deforms the ice immediately (See [b] in Figure It takes a lot more tension to deform the ice perpendicular to slip planes (see [ c] in Figure 1):
| Figure 1: [a] The hexagonal ice crystal with glide planes parallel to the base of the water surface. [b] crystal deformed plastically by shear stress parallel to the slip plane. [c] Elastic deformation of the crystal for tension perpendicular to the slip planes. Grains in such guidance molecules that deliver to lose the least stressed crystals, which become larger. This is why ice crystals pray in size towards the foot of the glacier, a matter not simply explained if the ice to slide on its base. |
flujotes
Another important method in the ice "normal." There is a constant gain and loss of atoms between different crystals in a mass of ice, and the absence of tension, an individual grain of ice lost the same amount of atoms to win, so it remains unchanged. But if a crystal is stressed lose more atoms of winning and thus be reduced, while a close grain, without tension, wins more atoms of losing and thus grow. In this way there will be a preferential gain in those crystals that are oriented so that their glide planes are parallel to the tension, and the grains with other orientations will tend to disappear.
 Figure 2: The tongue of the glacier is the lower end thereof, also known as the end or foot of the glacier. This is a glacier at the head of Canon Fiord, Ellesmere Island, Canada (Source: National Snow and Data Center). |
This is observed in glaciers where a preferred orientation of the crystals appears to distance down the valley, and ice crystals in the glacier tongue has a volume a thousand times greater than the first crystals formed in the source glacier. These observations can not be explained by mechanisms that ignore the crystal structure of ice. How can flow
a solid? In the case of ice, it does for the process called 'creep', that was not understood until the days of X-ray crystallography. The ice crystals are as a club of cards that can move smoothly over the other with ease. The ice of the lake, the planes are parallel to the surface of the lake, and that kind of ice is deformed under very low voltages. If a crystal is not in position to slide, jump atoms of crystals stressed to less stress, so that the latter grow at the expense of the former.
flow in a solid crystalline material known as 'creep', and there are three laws of creep relevant to the flow of ice:
- Creep is proportional to temperature.
- Creep is proportional to pressure or stress (essentially proportional the weight of ice in the upper layers.
- There is a minimum stress, called 'yield stress' below which creep does not occur.
All these laws have a significant effect on the movement of glaciers, alpine glaciers differ significantly from the ice sheets of Greenland or Antarctica, and care must be taken to transfer knowledge from one class to another glacier. Incidentally, the physics of ice described here were developed to over 60 years by people such as Perutz (1940).
Creep is proportional to the temperature
 Figure 3: Glacier valley in the north central part of the MONTANS Chugach, Alaska. (Source: USGS) |
The closer the melting point temperature, the higher the rate of creep. In experiments at a fixed voltage, it was found that the rate of creep to 1 degrees Celsius is 100 times greater than 20 degrees Celsius. He will valley glaciers (glaciers formed in mountain valleys, see Figure 3), the ice is almost everywhere in the prevailing point of melting ice because the latent heat of ice is much larger than its specific heat.
very little heat is required to raise the temperature of a block of ice from -1 º C to 0 º C, making 80 times more heat to transform the same block of ice at 0 º C in water 0 ° C. Since the temperature does not vary in the mountain valleys, the first law of creep does not affect [3]
[3] - The ice flows faster when it is near the melting point. In alpine glaciers (or mountain) glaciers at the edges of the ice sheets are all near the melting point, but in the middle of the ice temperature is well below melting point and the flow is absent or very low.
But the ice sheets are very different. They are frozen by temperatures well below freezing, which greatly reduces its ability to flow. Ice sheets can be miles thick, and its hottest part is actually the base, where the ice is melted by the heat of the earth, and where flow is concentrated. This was evidenced by the fact that drilling in the Ice Drilling Project in Northern Greenland (NGRIP, by Northern Greenland Ice Core Project) was arrested by relatively high temperatures near the base. We had to design a new cutting tools from 3001 to 3085 only meters. Q must be the ice only flows at the base that can accumulate a large stratified ice thickness, as revealed by ice cores.
helo Some cylinders show no flow. This is cold-based ice. A large literature describes geomorphological landforms such as cliffs and delicate patterns land in areas that were previously covered by a layer of ice. The general view is that cold-based ice preserved, essentially, any pre-existing landforms, and erosion potential of cold-based ice is zero or minimal. Important
ideas of "collapse", the ice is slipping: not move at all. Greenland differs from the Antarctic ice sheet that is poured through openings in the border mountains, and glaciers are on deep, narrow valleys. According to van der Vee et al., (2007), these valleys have a higher geothermal gradient than normal, so you can be geothermal heat, rather than global warming, the cause of several glaciers in Greenland have higher flow rates than normal. Spills are some of the features of alpine glaciers, where evidence of glacier recession is more obvious.
Creep is proportional Tensile
is, proportional to the weight of ice on top. This means that the heavier the faster ice flow. This is shown in the thick of undisturbed ice revealed by the ice cores that are used for paleoclimatic studies. In Antarctica, Vostok cylinders that provide the desired information continued to a depth of 3310 meters or 414,000 years, but, but below this depth, the ice begins to deform.
There is a minimum voltage, output voltage, below which creep does not operate. On the surface there is no tension, so that no ice flows, to a certain depth the weight of ice is enough to cause flow, and all the ice below this limit must flow. The boundaries of this threshold between ice and ice does not flow flowing marks the position of the yield stress and the transition from ice to ice brittle plastic.
in Antarctica and Greenland deep cracks occur towards the edges where the ice is flowing. But not in the areas of accumulation. In the middle of the ice sheets are not screaming to transmit water to the base of the ice, even if present (which is impossible).
Some Results of Laws the Flow of Glaciers
These simple rules of creep us understand some observations on glaciers. Advance
Glacier Brusco ('comes')
The speed of valley glaciers has been measured for a long time and is quite variable. Sometimes a valley glacier flow several times faster than before. Suppose we have a period of fifteen years of heavy precipitation. This will cause a thickening of the ice and a faster flow of the glacier. The faster flow pulse will eventually pass down the valley. It is important to understand that increasing the flow rate is not related to the current air temperature, but precipitation long ago.
melt and Climate
The July 21, 1983 recorded the lowest temperature measured on Earth reliably with 89.2 degrees Celsius. The highest recorded temperature at Vostok is 19 º C below zero, which occurred in January 1992. During the month of June 1987 the temperature never rose from 72.2 º C below zero. At these temperatures ice can not flow under the pressures that prevail near the surface. Warming has no effect at such low temperatures: the ice will not flow faster at 60 degrees Celsius at 70 degrees Celsius.
Ice sheets may take many thousands of years to flow from the accumulation area to the melting area. The balance between movement and melting time is unrelated to the current climate, but climate several thousand years ago.
Glaciers and Precipitation
Glaciers and ice sheets are in a state of semiequilibrio, governed by the rates of accumulation and melting. For a glacier maintain its current size should be rainfall at the source or header. This leads to a slightly complex relationship with temperature. If the regional climate becomes too dry, no rain so the glacier will diminish. This could occur if the region becomes cold enough to reduce evaporation from the ocean. If the temperature rises, evaporation increases and l therefore be capped. Paradoxically, a regional temperature increase could lead to a growth of glaciers and ice sheets. For example, the current ice sheets of both Greenland and the Antarctic is growing by the accumulation of snow.
The Age of Ice Sheets
The drilling of ice in Greenland has more undisturbed decorate miles of ice that dates back over 105,000 years, far less than the equivalent in Antarctica. The Vostok drilling provide data for the past 414,000 years before the ice began to deform. The drilling of the Dome F "reached 3035 meters and" Dome C "3309 meters, and both date back to 720,000 years ago. Epica drilling in Antarctica and goes up to 760,000 years ago as they do Guliya ice cores from Tibet. But what is more important than age is the great thickness of ice is preserved, and retains a complete record of deposition, despite the fact that temperatures have sometimes been higher than now. These records do not conform to the model of surface melting, even infrequently. After three quarters of a million years of documented continuous accumulation, how can we believe that right now the world's ice sheets are collapsing!
The Collapse of Ice Sheets
Some of the current claims that the ice sheets 'collapse' are based on misconceptions. Ice sheets do not melt from the surface down-just do it at their edges. Once the edges have been lost, a subsequent loss depend on the rate of ice flow. The rate of flow of an ice layer does not depend on current climate, but the amount of ice already accumulated, and that will continue to flow for a very long time. It is possible that any increase in temperature causes an increase in snowfall, so feeding the growth of the ice sheet, not diminishing.
ice cylinders used to determine the climate during the past 400,000 years also show that the ice has grown during that period by accumulation of stratigraphic layers of snow, and have not been deformed or remelted. The mechanism portrayed by Christofferson and Hambrey (2006), by which meltwater lakes on the surface find their way through cracks and crevices in the ice, lubricating the bottom of the glacier is not compatible are the accumulation of undisturbed snow layers. Could conceivably occur in valley glaciers, but nothing says the collapse of ice sheets. Conclusion
warming doomsayers say helo sheets of Greenland and Antarctica are melting catastrophically, and cause a sudden rise in sea level of five or more meters. This ignores the mechanism of glacier flow, which is made through creep. Glaciers do not melt from the surface down, nor are sliding along an inclined plane lubricated by meltwater. The existence of an ice cover over three miles of ice that preserves the details of the old snow and the atmosphere used to decrypt the CO2 levels and temperature, show that ice sheets have accumulated for hundreds of thousands of years without melting. Variations in melting around the edges of the ice sheets are no indication that Eten collapsing. Indeed, the "collapse" is impossible. References
- Appenzeller, T. (2006), “The Big Thaw,” National Geographic, June 2007: 56-71.
- Bamber, J.L., Alley, R.B. and Joughin, I. (2007), “Rapid response of modern day ice sheets to external forcing,” Earth and Planetary Science Letters, 257: 1-13.
- Carlin, A. (2007), NCEE Working Paper #07-07: http://yosemite.epa.gov/ee/epa/eed.nsf/ WPNumberNew/2007-07?OpenDocument.
- Christoffersen, P. and Hambrey, M.J. (2006), “Is the Greenland Ice Sheet in a state of collapse?” Geology Today, 22: 98-103.
- De Saussure, H-B. (1779-1796). Voyages dans les Alpes.(4 volumes) Manget, Geneva.
- Hansen, J. (2007), “Scientific reticence and sea level rise.” Environmental Research Letters, 2(2): < href="http://www.iop.org/EJ/article/1748-9326/2/2/024002/erl7_2_024002.pdf"> http://www.iop.org/EJ/article/1748-9326/2/2/024002/erl7_2_024002.pdf.
- Perutz. M.F. (1940), “Mechanism of glacier flow,” Proceedings of the Physical Society, 52: 132-135, 1940.
- van der Veen, C.J., Leftwich, T., von Frese, R., Csatho, B.M. & Li, J. (2007), “Subglacial topography and geothermal heat flux: Potential interactions with drainage of the Greenland ice sheet,” Geophysical Research Letters, v.34, LI2501, doi:10.1029/2007 GL030046.
By: Cliff D. Ollier *
Center for Science & Public Policy
Frontiers of Freedom Institute (*) School of Earth and Geographical Science,
The University of Western Australia, Crawley, WA 60009, Australia
Source: Myths and Frauds
