by Wm. Robert Johnston
last updated 29 December 2005
(See Comments on global warming for a general discussion of the science of global warming.)
I have discussed the first four points (which are non-trivial and deserve extended discussion) in Global warming, Some scientific data on global climate change, and "Facts disprove warnings about global warming", and the fifth point in Facts and figures on sea level rise. I will mostly address the last point--not just to dispel the notion that we need worry, but also because it is a valid and interesting thing to be curious about.
I. The world's ice
Currently the Earth has permanent ice in the icecaps of Antarctica and Greenland, plus much smaller permanent glaciers in various mountain regions of the world. This ice is "permanent", however, only over the short timespan of modern human civilization. Additionally there are two large ice sheets floating in seas off Antarctica, plus floating pack ice in the Arctic Ocean and surrounding Antarctica. Geological evidence indicates very clearly that at times in the Earth's past icecaps were much larger in extent--and alternately, at other times icecaps were virtually nonexistent.
Currently there are about 30,000,000 cubic kilometers of ice in the world's icecaps and glaciers. This volume of ice is fairly well measured (within 5-15%) by surveying the top of the icecaps with methods like radar and laser altimetry, locating the bottom of the ice with methods like seismic soundings, and calculating the difference. A breakdown is as follows:
|Location||Volume (km3)||Fraction of|
|Change in volume|
since 1960 (km3) **
|Continental glaciers and ice fields*||87,000 (± 10,000) ||0.29 %||-4,700 [2,3,4]||grounded|
|Greenland ice cap||2,930,000 (2,620,000 to 3,000,000) [5,6,7,8,9]||9.8 %||-2,000 [6,10,11,12,13,14]||grounded|
|Greenland continental glaciers||~50,000 (± 20,000?) ||0.17 %||-350 [3,4]||grounded|
|Arctic Ocean pack ice||16,000 summer, 24,000 winter [16,17]||0.01 %||-3,000 [16,18,29]||floating|
|East Antarctic Ice Sheet||23,000,000 (21,800,000 to 26,040,000) [5,6,8,19]||76.8 %||+10,000 [6,20,21]||grounded|
|West Antarctic Ice Sheet||3,000,000 (3,000,000 to 3,260,000) [5,19]||10.0 %||-4,500 [21,22,23]||grounded|
|Antarctic Peninsula ice cap||227,000 [5,24]||0.76 %||(included with EAIS)||grounded|
|Antarctic continental glaciers||~50,000 (± 20,000?) ||0.17 %||-700 [3,4]||grounded|
|Ross Ice Shelf||230,000 ||0.77 %||-2,000 [26,27]||floating|
|Ronne-Filcher ice shelves||344,000 ||1.17 %||-2,000 [26,27]||mostly floating|
|South polar pack ice||4,000 summer, 19,000 winter ||0.08 %||+100 ||floating|
|Total world ice||~29,960,000||100 %||-9,150|
|--grounded ice only||~29,340,000||97.9 %||-2,250||grounded|
|--floating ice only||~620,000||2.1 %||-6,900||floating|
Grounded ice is ice resting on the ground rather than floating. The melting of floating ice will not change sea level: the mass of this ice is equal to that of the water it displaces (watch the water level in a cup of floating ice cubes as they melt). For comparison, globally ice (both grounded and floating) represents about 2% of the world's water, with about 1,350,000,000 km3 of water in the oceans.
During the last Ice Age the maximum extent of glaciation was around 16,000 B.C. At that time large ice sheets covered all of Canada, much of the American midwest and northeast, all of Scandinavia and some surrounding regions of Eurasia. The total volume of ice then was perhaps 80,000,000 cubic kilometers, or between two and three times as much as today. Correspondingly, world sea level was about 120 meters lower [6,30].
II. Why melting is not a threat
While today's balance between the icecaps and global sea level has been relatively steady since about 1000 B.C., it would be careless to assume that this is the Earth's natural state and that it should always be this way. What could happen to climate naturally in the next few thousand years? If the Earth continued to warm and break from ice age conditions, some of the remaining ice caps could melt. On the other hand, climate might swing back into another ice age. (In fact, some of the environmentalists now worried about global warming were worried about another ice age in the 1960s and 1970s.)
In either case, such a change in climate would take thousands of years to accomplish. Note that it has taken 18,000 years to melt 60% of the ice from the last ice age. The remaining ice is almost entirely at the north and south poles and is isolated from warmer weather. To melt the ice of Greenland and Antarctica would take thousands of years under any realistic change in climate. In the case of the East Antarctic Ice Sheet, which accounts for 80% of the Earth's current ice, Sudgen argues that it existed for 14,000,000 years, through wide ranges in global climate. The IPCC 2001 report states "Thresholds for disintegration of the East Antarctic ice sheet by surface melting involve warmings above 20° C... In that case, the ice sheet would decay over a period of at least 10,000 years."  The IPCC is the United Nations' scientific committee on climate change; its members tend to be the minority that predicts global warming and its statements tend to be exaggerated by administrators before release. Given that the IPCC tends to exaggerate the potential for sea level rise, it is clear that no scientists on either side of the scientific debate on global warming fear the melting of the bulk of Antarctica's ice. Consider also this abstract of an article by Jacobs contrasting scientific and popular understanding:
A common public perception is that global warming will accelerate the melting of polar ice sheets, causing sea level to rise. A common scientific position is that the volume of grounded Antarctic ice is slowly growing, and will damp future sea-level rise. At present, studies supporting recent shrinkage or growth depend on limited measurements that are subject to high temporal and regional variability, and it is too early to say how the Antarctic ice sheet will behave in a warmer world. 
This statement alludes to the significant point that the Antarctic ice cap appears to currently be growing rather than shrinking. In fact, were the climate to warm significantly in the next few centuries (not a certain future, but supposing it happened), current models suggest that Antarctica would gain ice, with increased snowfall more than offsetting increased melting.
How much concern should we have about the 20% of world ice outside the East Antarctic Ice Sheet? Some sources have recently discussed the "possible collapse" of the West Antarctic Ice Sheet (WAIS). It is suggested that this sheet (about 10% of Antarctic ice) could melt in the "near term" (a usefully vague phrase) and raise sea level 5 to 6 meters. Current understanding is that the WAIS has been melting for the last 10,000 years, and that its current behavior is a function of past, not current climate.  The abstract of an article by Alley and Whillans addresses this:
The portion of the West Antarctic ice sheet that flows into the Ross Sea is thinning in some places and thickening in others. These changes are not caused by any current climatic change, but by the combination of a delayed response to the end of the last global glacial cycle and an internal instability. The near-future impact of the ice sheet on global sea level is largely due to processes internal to the movement of the ice sheet, and not so much to the threat of a possible greenhouse warming. Thus the near-term future of the ice sheet is already determined. However, too little of the ice sheet has been surveyed to predict its overall future behavior. 
Similarly, recent stories have periodically appeared concerning the potential receding of the Greenland ice cap. Two points may be made regarding current understanding here. First, there is considerable disagreement as to the current rate of net ice cap loss--or even if there is net loss versus net gain. Second, even with temperature increases far greater than the dubious predictions of the IPCC, models indicate that Greenland's ice cap would take 2,000 to 10,000 years to disappear.
Some discussion of the concerns about near term sea level rise may be found in Facts and figures on sea level rise. The predictions that have been made for ice cap melting in the next century rely mostly on melting of glaciers in mountain regions, not melting of the polar ice caps. Even the pessimistic models cited by the IPCC tend to predict an increase in the volume of the Antarctic ice cap with warmer temperatures due to increased snowfalls. In general temperature changes of a few degrees do not seem to be sufficient to begin to melt the polar ice caps, particularly the Antarctic ice cap.
III. Imagining the world without ice caps
As long as we understand that the polar ice caps are not going to melt in the foreseeable future, we can proceed to imagine what the world would be like if they did melt.
Using the ice volume figures from above it is straightforward to estimate the effect on sea level were all this ice melted. Melting the 29,300,000 km3 of grounded ice would produce 26,100,000 km3 of water. Note that melting of floating ice has no effect on sea level. Also, about 2,100,000 km3 of the grounded ice in Antarctica is below sea level  and would be replaced by water. Thus, the net addition to the world's oceans would be about 24,000,000 km3 of water spread over the 361,000,000 km2 area of the world's oceans, giving a depth of 67 meters. The new ocean area would be slightly larger, of course, since some areas now land would be covered with water. The final result would be around 66 meters (current estimates range between 63 and 75 meters).
What would the Earth look like as a result? If sea level were 66 meters higher than today, the result would be as illustrated below (for the map I used below see this page):
Obviously some areas are affected more than others. Some larger areas now underwater are the southeastern United States, part of the Amazon River basin, northern Europe, Bangladesh, parts of Siberia along the Arctic Ocean, and portions of mainland China. A large area in Australia would be below sea level, but it is not joined to the ocean and could remain dry.
Above is a view of the lower 48 states of the United States with a 66-meter-higher sea level. Below are some closeups:
Both Greenland and Antarctica, free of ice, have areas that would be below sea level. However, with the weight of this ice removed, Greenland and Antarctica would rise higher--this phenomena is called isostatic rebound. This rebound lags behind the removal of the ice (by thousands of years). Eventually, most of Greenland would probably be above sea level. However, significant portions of Antarctica would remain underwater. This is shown below in a view of the southern hemisphere:
Today the Earth has 148 million sq. km of land area, of which 16 million sq. km is covered by glaciers. A sea level rise of 66 meters would flood about 13 million sq. km of land outside Antarctica. Without polar ice, Antarctica and Greenland would be ice free, although about half of Antarctica would be under water. Thus, ice-free land would be 128 million sq. km compared to 132 million sq. km today.
As a result, in terms of total habitable land area, the Earth might have more than today. The coastal areas reclaimed by the sea would be mostly offset by now habitable areas of Greenland and Antarctica. Again, remember that such climate change would take thousands of years. Over such time scales vegetation would be restored to newly ice-free regions even without human activity. Also, vast areas which are now desert and tundra would become more fit for human habitation and agriculture.
The illustrations above do not depict any changes in vegetation. In reality, local climates would be very different in ways that are currently difficult to predict. It might be that the warmer climate would lead to generally greater precipitation (this is suggested by comparison to the last ice age, when cooler temperatures caused expansion of the Sahara). Unfortunately, current models are not reliable enough to give a confident answer.
So why wouldn't people drown? Again, a change in the Earth this dramatic would take thousands of years to effect from any realistic cause. Over generations people would migrate as the coasts changed. Consider that virtually all of the settlements in the United States were established only in last 350 years. Of course, many settlements inhabited for thousands of years would have to be abandoned to the ocean--just as many would have to be abandoned if ice age conditions returned and covered vast areas with ice sheets. But people can comfortably adjust where they live over periods of decades, far shorter than the thousands of years needed for these climate changes to naturally take place. Also, that's if they occur, and we have no evidence to indicate what would happen to climate over the next few thousand years.
IV. A final comment
For those curious as to what the Earth would be like with the ice caps melted, this report has hopefully given an illustration, along with some perspective: this sort of change cannot be affected by modern human activity even given many centuries. It is sad that some youngsters think that burning of hydrocarbons could cause the ice caps to melt and drown cities; it is criminal when teachers don't correct this nonsense. And it should tell you much of environmental groups like the Sierra Club when they use such myths to further an extremist political agenda.
© 2002-2003, 2005 by Wm. Robert Johnston.
Last modified 29 December 2005.
Return to Home. Return to Environmental Topics.