One of the most depressing effects of global warming is the rise in sea levels. Scientists often use the famous biblical legend about the Noah's ark to illustrate their alarming predictions - that is, they say, what awaits humanity in the near future.
However, such statements about the coming widespread attack of water are very dramatized. According to new studies, the melting of ice will not lead to a catastrophe of a universal scale at all: no matter how strange it may sound, in places the water, on the contrary, will recede, exposing large areas of land.
To begin with, let's see why glacier melting affects ocean level in general. For example, if you put pieces of ice in a container with water, its level will not change when they melt. Thus, the disappearance of the Arctic ice itself should not significantly affect the boundaries of the sea and land. But the ocean, as measurements show, still comes, and this happens for the following reason: when the water becomes warmer, it, like most substances, expands, and its outflow from the glaciers ultimately increases the volume of the ocean.
Ecologists have long been saying that if the ice caps melt completely, the sea level will rise by an estimated seven meters. For some coastal and port cities, this can be a disaster. Against the backdrop of these apocalyptic predictions, the theory of a decline in sea level seems absurd at first glance, especially considering how long we have been intimidated by the coming flood. Specialists should have weighty arguments in order to radically correct their point of view.
However, it should be noted right away that we are not talking about the average indicators of water growth - the ocean continues to rise steadily, taking away about three centimeters a year from land. It's just that in practice, these changes are extremely uneven - the gravity and geographical features of the ocean floor in the Antarctic region make their significant amendments. The scientific community has long ignored these factors, but now, when they are taken into account, it turned out that in some parts of the world the ocean will indeed recede from the coast.
The seabed has a definite relief with its own hills and lowlands, and the height differences reach at least several tens of meters. And heavy ice masses have not the last effect on the formation of the earth's crust: tectonic plates sag under their weight, but along the edges of ice accumulations, the surface, on the contrary, "swells", lifting up the islands located above it. Oceanographers drew attention to such transformations of the earth's surface back in the 19th century when studying the impact of glaciers in North America and Eurasia.
Under the weight of the ice masses, the planet's surface bent as much as five hundred meters. At the end of the ice age, the crust began to recover, and, despite the past 20 thousand years, this process has not yet been completed. For example, even now the Hudson Bay area is adding an inch per year, and some elevated regions are still sinking.
Similar tectonic processes will invariably be launched even with the current melting of ice. The bottom topography in the Antarctic regions will undergo changes: the plates, freed from the icy weight, will return to their rightful place, and the regions along the edges of the glacier will begin to sink. Scientists are now trying to predict how the changed position of seamounts and troughs will affect ocean level. The conclusions are ambiguous: Boston and New York, for example, will find themselves in a flood zone, while Scotland, on the contrary, will have more "dry" areas.
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But the topography of the earth's surface is not the only factor influencing the behavior of the ocean in the light of global warming. In the same 19th century, physicist Robert Woodward of the US Geological Survey proposed the gravitational effect of ice sheets on the surrounding water. According to his findings, glaciers, like any other massive objects, are capable of attracting water, creating a kind of water slides around them.
Accordingly, melting will release not only water bound in the form of ice, but also water bound by ice gravity. Woodward's scientific research in 1976 was continued by William Farrell and James Clark, who tried to apply this theory when calculating sea level changes at the end of the last ice age.
A little later, Clark, guided by the theory of "glacial gravity", tried to calculate how the map of the Earth would change with the disappearance of the West Antarctic ice sheet. It turned out that although the average sea level will rise, in some areas of the Southern Ocean the water will drop.
Clark's research generated some interest in the scientific community, but in general, oceanographers continued to build simplified models of water distribution during global warming, without taking into account the gravitational effects of glaciers. In their studies, oddly enough, they stubbornly ignored even the readings of the TOPEX / Poseidon satellite, which in the 1990s confirmed the influence of gravity on the seascape.
But Jerry Mitrovitsa from Harvard University (USA) drew attention to this. It was through his efforts that the gravitational factor was later recognized in the scientific community. Mitrovica's team presented calculations in which not the last place was given to the "attractive force" of the glacier. The findings of the researchers shocked oceanographers: according to new data, as soon as the glacier melts, the water level will fall within a radius of about 2 thousand kilometers from it.
So, if Greenland disappears completely, the sea level off the coast of Scotland will drop by more than three meters, and in the Iceland region, the water will fall by all ten meters. Off the coast of Europe, only a slight rise in water is expected, at least not by the seven meters with which scientists previously frightened us. However, if in some regions the sea element recedes, then it will certainly win back in other areas of the planet. In particular, hard times will come for coastal cities in South America - there the sea level will rise by 10 m.
By the way, in addition to the gravitational effect, in calculating the change in the level of the world ocean, Mitrovica took into account one more factor, which was also previously overlooked - the influence of the glacier on the orientation of the Earth's axis of rotation. According to a geophysicist's research, when the massive ice sheet melts, the Earth's axis of rotation will shift by about half a kilometer, which will also affect sea level in various regions of the Earth.
For example, with the complete release of Greenland from ice and the subsequent displacement of the axis of rotation, the equatorial bulge will slightly tilt, as a result of which the underwater hills will grow in some places by half a meter.
However, one should not forget that along with Greenland, West Antarctica is the most important participant in the global warming process, and it can make certain adjustments to the distribution of water masses. Considered in isolation, the melting of its ice will lead to a decrease in sea level off the coast of Antarctica and a slight rise in water near the southern tip of South America. But the east coast of the United States, which, by the way, is still slowly sinking after the ice age, will have a hard time - there the sea level will exceed the world average by 25%.
Now scientists are faced with a difficult task: to analyze the consequences of melting of both Greenland and West Antarctica together and create a full-fledged model of the distribution of water masses, taking into account the outflow of water from both the north and the south of the planet. Greenland is now disappearing at a much faster rate than the Antarctic glaciers are melting, and this is undoubtedly sad news for South America.
However, West Antarctica still has a chance to overtake Greenland in melting, because a significant part of its glaciers is below sea level, and, as you know, warm water melts ice faster than air. In this case, taking into account the gravitational effect, one should wait for the retreat of water from the shores of Antarctica, and then the ocean pressure will have to be restrained by the inhabitants of the United States.
Be that as it may, the recognition of the factor of the gravitational effect of glaciers and its detailed study will make it possible to draw up a more detailed and true model of the coming changes in the relationship between land and water.
“From a disagreement over estimates of sea level rise, we are gradually moving towards a coherent theory that reconciles conflicting data from different geographic regions,” said Mark Siddall, a climatologist at the University of Bristol.
In the meantime, the experts are working hard to find out which water masses will be more energetic - from the north or from the south, we can only guess what will emerge and what will drown.
