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Earthworks & Systems, Climate Change

As the Earth Warms:
The Thinning of the Arctic Ice Cap

November 30, 2001

The geographic North Pole was last covered with water about 50 million years ago, during the early part of the present Cenozoic Era. Known as the |Age of Mammals2 and the |Recent Life Era,2 this modern age ? which saw the dawn of human beings 3 began 65 million years ago.

This global view of the Arctic Ocean, captured using advanced radar that sees through all weather conditions, is enabling researchers to determine how global warming may be affecting the Polar Ice Cap. The Arctic sea ice is providing clues to the Earth's overall climatic condition. (NASA Image)

During the Cenozoic Era, the continents which formed Pangea, the |super continent,2 had begun to move into their present positions. As these continents drifted northward, they formed the shoreline of the Arctic Ocean which lies directly over and around the geographic North Pole.

About 15 million years into the Cenozoic Era (about 50 million years ago), the Arctic Ice Cap formed over the Arctic Ocean, virtually covering the entire sea with a sheet of ice. As the continents continued to move, climatic changes brought about by shifts in water and air currents caused the Earth to gradually cool down. This created the glaciers that mostly dominated the land masses through the end of the Great Ice Age in the Pleistocene Epoch, about 10,000 to 1.8 million years ago, and that still exist today on Greenland.

The same climatic conditions that created the glaciers, which are essentially great ice sheets formed on land, also formed the Arctic Ice Cap. Yet the ice sheet covering the Arctic Ocean rests directly on top of the ocean instead of land, and it has remained relatively stable and frozen since it was formed... until now.

The Arctic Ice Cap is shrinking dramatically. Roughly the size of the United States, it has lost an area roughly the combined size of Massachusetts and Connecticut each year since the late 1970s. Since the 1950s, when data was first collected on the Arctic, the ice cap has lost nearly 22% of its volume. It is projected that in another 50 years, nearly half of the Arctic Ice Cap will be gone.

So what is going on? We know that the Arctic Ice Cap, frozen for 50 million years, is melting. We also know that above normal Arctic temperatures ? from the ocean water to the air currents ? account for the melting. Global warming is real, and the melting of the Arctic Ice Cap is one of its symptoms.

This chart compares the actual loss of Arctic Ice Cap volume between the 1950s and 2000, and the projected loss by 2050. The more ice that is lost, the faster the ice cap shrinks due to the loss of albedo, the amount of light energy that is normally reflected back out into space by the ice cap. (Image: NOAA)

Scientists have determined that the Earth's surface temperature has increased an average of 1? F since the beginning of the 20th century, which is enough to trigger significant global climatic changes. According to the United States Environmental Protection Agency (EPA), the 20th century was the warmest century of the last millennium, and the 1990s was the warmest decade. Increased average temperatures have been recorded in both the southern and northern hemispheres, although some regions have recorded cooler temperatures.

Using the best available data, many scientists believe this warming trend will cause an additional 5? - 10? F increase in the average global temperature in the next century. Still, there are many scientists who believe the global warming trend may reverse itself within the next century. The fact is, there is not enough known about WHY the climate is changing the way it is for scientists to determine what really is going on or what will happen in the future.

But there is enough information to tell us several things:

  1. 1) Human activity, such as the burning of fossil fuels, is releasing enormous volumes of carbon dioxide and other greenhouse gases that are contributing to the Earth's natural greenhouse effect ? the Earth's natural process of trapping the sun's warmth. About 5-6 billion tons of carbon dioxide are emitted each year due to human activity (Source: Ohio State University Department of Mechanical Engineering, printed in Science Daily). This increase results in additional heat being trapped within the Earth's atmosphere;

  2. 2) The Polar Ice Cap itself reflects sunlight energy (heat) back into space, rather than the heat being absorbed by the Earth. This is called albedo, the amount of sunlight reflected by an object. As the Ice Cap melts however, the albedo is reduced and the Earth absorbs the energy that is not reflected. Thus, more heat is retained in the Arctic;

  3. 3) The Earth's natural carbon cycling process ? the amount of carbon dioxide that enters and leaves the atmosphere as a result of the natural cycle of water exchange from and back into the sea and plants ? accounts for about 95% of the carbon dioxide in the atmosphere which contributes to the greenhouse effect;

Ocean waters constantly move along a giant oceanic conveyer belt which travels from the North Atlantic to the Atlantic, Pacific and Indian Oceans. This circulation distributes warm tropical waters northward, which are then chilled and returned to the warmer southern oceans. This heat exchange also has a significant impact on global weather patterns. (Image: NASA)

4) Ocean waters are constantly on the move, carrying warmer waters north toward the Arctic and cooler waters south to the temperate and tropical zones. This ocean circulation is referred to as the great oceanic conveyer belt, which is a single continuous current that carries chilled water from the North Atlantic into the Atlantic, Indian and Pacific basins. The conveyer belt returns water warmed in the tropics back to the North Atlantic.

5) Ocean currents also affect global heat exchange by redistributing heat, especially in coastal regions. In fact, the oceans have the greatest impact on the Earth's climate.

Putting It All Together

The point is, that while all of these things are taking place ¤ at the same time ³ none of them exists in a vacuum. They are all interrelated and can have a reciprocating effect on each other. To what extent, scientists do not know at this point.

The climatic changes that are taking place can have profound impacts on the Earth's ecosystems, human health, plant and animal species. Scientists fear that continued melting of sea ice could weaken the North Atlantic Current, the northward continuation of the Gulf Stream. The Gulf Stream transports 25 times more water than all the Earth's rivers, and a diversion could result in extremely cold winters in the North Atlantic regions, especially in northern Europe (Source: US Geological Survey).

There are many-fold scenarios; however, human-induced global warming is one that we should pay close attention to because we can control it. If we can reduce carbon-dioxide emissions, it could have a penetrating effect on the natural climatic occurrences that have been affected by human activity. Scientists project that the amount of carbon dioxide released into the atmosphere in the next 30 years will or triple. The number of cars in operation around the world will double by the year 2030.

Arctic Ice Deluge?

One concern that most people have with regard to the melting of the Arctic Ice Cap is the eventual flooding of the land masses. What is commonly misunderstood is that the Arctic Ice Cap is relatively thin, about 10 feet thick on average. And about 90 % of that is already displacing the water (taking up space that would otherwise be occupied by water). Thus, even a complete melting of the Arctic Ice Cap would only result in a small increase in sea water level.

Antarctica is a continental land mass 98% covered by thick ice sheets. It contains 70% of Earth's fresh water and 90% of Earth's ice. The average ice thickness is 1.5 miles, reaching 3 miles deep in some regions. (Image: NASA)

The major concern, however, would be the increase of fresh, cold water into the marine environment. This would alter ecosystems and the food chain dependent on the saline waters and would funnel more cold water into the oceanic conveyer belt. As a result, you would see a global climate change due to the introduction of the additional cold water into the southern oceans, and you would see a displacement of plant and animals species dependent on the more saline ecosystems. Some animal species will, of course, retreat to the land-based ecosystems.

On the Opposite End of Earth

Antarctica, which covers the geographic South Pole, is itself covered with thick ice sheets. The average ice thickness is about 1.5 miles with some parts reaching as deep as three miles. Antarctica's ice shelves are also melting, for the same reasons associated with the melting of the Arctic Ice Cap, but not as dramatic. The melting of the Antarctic ice shelves has resulted in the ¦calving² of some of the largest icebergs ever known to exist, such as the series of icebergs that broke off from the Ross Ice Shelf in the spring and summer of 2000 (see ecology.com story, "Largest Existing Iceberg is Born". But dramatic melting of Antarctic ice would have enormous impacts on ecosystems, climate and sea levels.

-- Eric McLamb, with contributions from Dr. Jack Hall

Icebergs result from a melting of the Antarctic ice shelves and the Arctic Ice Cap. While the Arctic icebergs (above, right) are normally taller, the Antarctic icebergs (left), are much larger and more massive. Pictured, left, is one of the largest icebergs ever seen, B-15, which broke off from Antarctica's Ross Ice Shelf in the spring of 2000. (NOAA)

 

Did you know...?

  • Hot springs and active volcanoes have recently been discovered far beneath the Arctic Ice Cap in the Arctic Ocean. While the enormous heat and energy from this activity are insignificant contributors to the increase in ocean temperatures, they appear to be an oasis for newly discovered species of plants and animals.

  • Antarctica is colder than the Arctic even though during the course of the year it receives almost the same amount of sunlight. In fact, Antarctica receives a little more solar energy than the Arctic because the Earth is closest to the sun in December when Antarctica has 24 hours of sunlight.

  • The Arctic is the northern pathway that water travels between the Atlantic and Pacific oceans.

  • The greenhouse effect maintains Earth's average temperature at approximately 60Š F. Without the greenhouse effect, the temperatures on Earth would be so cold that life could not exist.

  • Sea ice is almost all fresh water, with some salt trapped within it. The salt is actually not part of the ice, but just got caught up in the freezing process.

  • The Arctic's ice is, at most, only a few feet thick with water under it. While the water would be anything but warm if you jumped into it, it is at least around 30Š F ³ it's salt water and stays liquid at a lower temperature than fresh water.

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