(an extract from www.thewe.cc/weplanet/poles/kalaall.html#abrupt. Follow the link to find further information about Greenland, and greater detail about the impacts of global warming. Thanks to Kewe for use of the material posted on this site)

The vast ice sheet covering Kalallit Nunaat (Greenland) is thinning by up to a metre a year.   Between 1993 and 1998 aerial surveyors from NASA found through laser altimeter technology that the ice sheet had lost an average of five metres in thickness.

On the western side of the icecap, some areas grew while others shrank.   But there was thinning almost everywhere else on the ice sheet.

As the ice cap is more than 3 kilometers thick this shouldn?t seem like much of a problem.   Yet scientists are saying the discovery of the thinning poses a potential threat to coastal communities around the world.   The ice sheet, which covers seven-eighths of the land?s surface, contains an estimated 11 percent of the world?s fresh water.

Ice core drillings of the ice fields of Kalaallit Nunaat do not date as far back as drillings of the Antarctic high plateau, but one advantage of drilling in the northern Arctic fields is that because of greater snow accumulation, and less compression of the ice, climatic history is preserved with a years-to-decades resolution, in contrast to the century-to-millennial scale resolution that has until recently been the findings in the Antarctic cores.

Over great periods of time there have been continental ice sheets that have advanced, spreading widely across lowlands in the north.   These are known as glacial periods.   During the last million years there have been four major glacial periods.   In chronological order they are the Nebraskan, the Kansan, the Saale, and the Warthe-Weischel.

An interglacial period is a time during which continental ice sheets that have advanced during a glacial period are caused to retreat for a lesser period of time to higher ground by warming.   Interglacial activity acts within a glacial period

There are also warming periods during the course of a major glacial stage that is not warm or prolonged enough to be deemed as interglacial.   These even shorter time periods are called interstadial.   Short cooling periods are called stadial.   The change in direction between these short warming and cooling periods are known as Dansgaard-Oeschger fluctuations.

During the last 110,000 years it is believed there have been at least 23 interstadial, ice warming, periods on the land of Kalallit Nunaat.

The discovery of abrupt climatic shifts, or Dansgaard-Oeschger oscillations, has been the most surprising feature of the Kalallit Nunaat ice core data.   The last glacial period show temperature increases over Kalallit Nunaat of up to 6 degrees Celsius, in a time span of less than a decade.   This has prompted great interest in the causes of such a dramatic change, and has led to speculation that the current increasing levels of greenhouse gases in the atmosphere might trigger such change in the coming decades.

Data in the ice cores do show differences, and the comparison between cores remains at this time scientifically inconclusive.   It is possible one core is being affected by a distortion of the ice sheet close to bed-rock.   There might be a folding or sheer effect of the bed-rock region below 2,700m depth.   Which core has the more valid data is not known.   The top 1,500 meters of both cores show clearly the remarkable climate stability of the Holocene these past 10,000 to 12,000 years ? the time period since the last glacial epoch ended.

Thermohaline Circulation

It is thought that the Dansgaard-Oeschger fluctuations might have been caused by major changes in the ocean?s thermohaline circulation.

Sixty percent of the heat built up around the equator is moved North and South by ocean currents.   The North Atlantic circulation system carries warm surface water northwards and returns cold deep water to the south.   Scientist?s call the deepwater ocean circulation that occurs through temperature cooling and salinity changes the ?Thermohaline Circulation.?   When warm surface water from the tropics reaches Kalaallit Nunaat and the high West Atlantic, it becomes cooled.   This surface water has a greater salinity than Arctic water due to evaporation, and the higher density causes the mixture of waters to sink in the cooler temperatures.

The halocline waters (vertical mixing) forces the densest, most saline water to sink to a deep subsurface.   Here it begins to turn towards the continental slope.   First the underwater current turns westwards, then south.   These narrow underwater flows continue alongside the base of the continental slope, flowing by the North and South American coast, until they reach the Antarctic circumpolar current.   Here some of the undercurrent begins to move into the Indian and Pacific oceans.

The circular movement of these flows show an upwelling around the northeast African coast, as also in the high Pacific waters.   The Pacific surface current flows northwards to about 50 degrees north and then eastwards.   Along the west coast of North America it turns south and then west, rejoining the surface current returning from the Indian Ocean.   Joined, this warmer surface water then moves around the tip of Southern Africa, up the coast of Africa and the European coast, turning west to Kalaallit Nunaat.   One complete circuit of this flow of seawater is estimated to take about 1,000 years.

Global Warming

The modeling of atmospheric and ocean processes indicate that if ice continues to shrink in the Arctic, due to global warming, two changes will take place:

The exposed ocean water will reflect less solar rays than ice.   This causes a further warming of the atmosphere.   Without other factors intervening, the additional warming will lead to more breakup of ice.

Additional melt water from the ice will bring large fluxes of freshwater into the north Atlantic causing a buoyancy effect from the much less saline water.   The cold waters will cease to sink, and the low undercurrent flow is likely to considerably weaken, halting the Atlantic thermohaline circulation.

All these processes are extremely complex.   The North Atlantic Drift is a warm ocean current in the northern part of the Atlantic Ocean that moderates the climate of Europe.   This is a continuation of the Gulf Stream, a western boundary surface current of the North Atlantic.   The Gulf Stream, a major part of the clockwise-rotating system of currents in the Atlantic, the North Atlantic Drift, and other currents will be affected by a large influx of freshwater.

With less ice cover, formation of the North Atlantic Deep Water (NADW) will likely increase.   NADW forms when waters from the oceanic thermocline upwell to the surface, cool, and sink in the seas around Greenland.   Heat is transferred from ocean to atmosphere in the process.   When seas are ice covered, NADW formation is generally slower.   An intensification of NADW formation would cause rapid warmings in Kalaallit Nunaat and other land masses adjacent to the North Atlantic, which can explain the impressive magnitude of the climate changes as well as their rapidity.   These dramatic climate changes discovered have not been to Kalaallit Nunaat and nearby areas alone, as evidenced by other records.

It is also worth noting that most of the 23 Kalaallit Nunaat interstadial events observed are not yet associated with major changes in Antarctic climate.   However, at least eight of the nine Kalaallit Nunaat events lasting longer than 2,000 years are linked to periods of warmer climates in East Antarctica.   Only the Antarctic Peninsula is warming at this time.   East Antarctica is cooling slightly.

Further study is needed to bring a clarification of all the factors involved in the complicated aspects of global warming.

However there is evidence of the aftermath of melting ice caps.   Marine sediment data, pollen profiles, and glacial snow line data all show that melting ice sheets in previous times have caused climactic changes that have been felt on a global scale.   These changes have occured over a very short period of time, some perhaps as short as ten years.

A record loss of sea ice in the Arctic summer 2005 has convinced scientists that the northern hemisphere may have crossed a critical threshold beyond which the climate may never recover.

Scientists fear that the Arctic has now entered an irreversible phase of warming which will accelerate the loss of the polar sea ice that has helped to keep the climate stable for thousands of years.

Dr Serreze: "This will be four Septembers in a row that we've seen a downward trend.  The feeling is we are reaching a tipping point or threshold beyond which sea ice will not recover."

Professor Wadhams: "As the sea ice melts, and more of the sun's energy is absorbed by the exposed ocean, a positive feedback is created leading to the loss of yet more ice."

"If anything we may be underestimating the dangers.  The computer models may not take into account collaborative positive feedback."

"Sea ice keeps a cap on frigid water, keeping it cold and protecting it from heating up."

"Losing the sea ice of the Arctic is likely to have major repercussions for the climate."

"There could be dramatic changes to the climate of the northern region due to the creation of a vast expanse of open water where there was once effectively land."

"You're essentially changing land into ocean and the creation of a huge area of open ocean where there was once land will have a very big impact on other climate parameters."