Greenland ice sheet collapse
The great ice sheet of Greenland was, traditionally, believed to take thousands of years to respond to external forcing. Recent observations suggest, however, that major changes in the dynamics of parts of the ice sheet are taking place over large timescales. Widespread thinning at rates generally exceeding those are expected to occur due to recent warmer summers as the atmospheric temperatures are rising. The main identified direct driver behind the loss of ice sheet volume is greenhouse gas emissions in atmosphere that initiate change in dominating reinforcing feedbacks. There are two initial feedback mechanisms that are maintaining the initial regime of the system – ice-albedo mechanism and meltwater-ice sliding mechanism. The options to prevent or reverse this potential regime shift mainly relates to the decrease of greenhouse gas input in to the atmosphere at a global scale.
Key direct drivers
- Global climate change
Key Ecosystem Processes
- Water cycling
- Wild animal and plant foods
- Climate regulation
- Water regulation
- Aesthetic values
- Cultural, aesthetic and recreational values
Typical spatial scale
Typical time scale
- Contemporary observations
Confidence: Existence of RS
- Contested – Reasonable evidence both for and against the existence of RS
Confidence: Mechanism underlying RS
- Well established – Wide agreement on the underlying mechanism
Links to other regime shifts
- Thermohaline circulation collapse
- Arctic Sea-Ice Loss
The Greenland Ice Sheet (GIS) is approximately 1.7 million km2 in areas covering approximately 80% of Greenland. It is grounded on bedrock that mostly rests near or above sea level thus would contribute to the globally averaged sea-level rise of 7.3 m if melted completely (Parizek et al. 2004, Lemke et al. 2007). Anticipated future climate warming has the potential to permanently reduce large areas of GIS or even abate it completely. The evidence suggests nearly total ice-sheet loss may result from warming of more than a few degrees above mean 20th century values, but this threshold is poorly defined (perhaps as little as 2oC or more than 7oC) (Alley et al. 2010).
Greenland with permanent ice sheet
This regime can be described as permanent ice body cover over major parts (~80%) of Greenland only exposing the bedrock in western and southern parts. The Greenland Ice Sheet has been more closely tied to temperature than to anything else. It shrinks with warming and grows with cooling, thus the volume and cover vary throughout the seasons, but in case of cold climate the relationship between the ice growth/decline would be approximately evenly balanced or with a slightly increased ice growth. In winter when the atmospheric temperatures decrease below freezing point and precipitation levels decline, the accumulation of the ice steadily increases (Bamber et al. 2007).
Greenland without permanent ice sheet
Due to the loss of the ice-sheet volume as a result of the warming, Greenland territory in future could become free from permanent ice sheet cover. This would happen as a consequence of the negative relation to ice growth/ice decline during the winter and summer where the lost ice volume in summer could not be reproduced in the following winter. Rising sea level as a result of warming tends to float marginal regions of ice sheets and force further retreat, so the generally positive relation between sea level and temperature means that typically both reduce the volume of the ice sheet (Alley et al. 2010).
Drivers and causes of the regime shift
Increasing greenhouse gas concentration from anthropogenic sources is predicted to cause a rise in global mean temperatures (Cubasch et al. 2001). One of the most common anthropogenic greenhouse gases is carbon dioxide (CO2). The influence of this driver is well established as confirmed by many studies. The indirect driver that is increasing anthropogenic CO2 levels in atmosphere is the burning of fossil fuels such as coal and natural gas. It is occurring regionally but has global impact and is well established in literature.
How the regime shift works
The initial regime would typically occur in cold climate conditions where the relationship between the ice growth/decline would be approximately evenly balanced or with a slightly increased ice growth. The two main mechanisms that maintain this regime are ice-albedo mechanism and meltwater-ice sliding mechanism.
Increasing CO2 levels in atmosphere - the key driver of the regime shift, initiates the increase of atmospheric temperatures and changes in albedo. As a result - increased absorption of solar energy promotes higher air, ice, water and land temperatures which leads towards degrading sea ice. Also the inland surface temperature increase can cause surface melting in the ablation zone that presently accounts for roughly half of the mass loss from the GIS (Parizek et al. 2004). Thus this driver indirectly is increasing drainage of meltwater feeding into crevasses close to the glacier margin resulting in higher calving rates (Murray et al. 2010). Furthermore, thinning and retreating of the glacier tongue due to these increased rates cause reduced effective pressures beneath the glacier, promoting faster flow that results in decrease of ice volume.
The increase in surface air temperatures changes the ice-albedo feedback thermodynamics. This means that the heat exchange within the sea ice, as well as between the top and bottom of the ice is changed. This leads to a decrease in sea ice volume. The resulting increased amount of open land and water surface in summer decreases the albedo, as the dark ocean surface absorbs more solar radiation (Lindsay et al. 2005). The annually integrated absorption of solar radiation is observed to increase when the surface albedo is relatively low (Rigor et al. 2002, Holland et al. 2006). This increasingly accumulated amount of heat on the surface reinforces the initial warming. Due to the loss of the ice-sheet volume as a result of the warming, Greenland territory in future could become free from permanent ice sheet cover. This would happen as a consequence of the negative relation to ice growth/ice decline during the winter and summer where the lost ice volume in summer could not be reproduced in the following winter. The Greenland without permanent ice sheet regime is characterized by other dominant feedback mechanisms. For example ice volume-wave action, the water temperature-density and meltwater-ice sliding velocity mechanisms.
Impacts on ecosystem services and human well-being
The shift to the regime of Greenland without ice sheet will mainly result in loss of some desirable ecosystem services. The ecosystem service of desirable climate regulation could be lost as the change in movement of currents (change in thermohaline circulation) and air masses would alter the transport of heat. This could lead to increased hurricane activity, a southward shift of tropical rainfall belts with resulting agricultural impacts, and disruptions to marine ecosystems.
The loss of certain animal and plant food species as provisioning services is predicted in the future. These changes may have important consequences for food webs and could well be extremely significant for the Greenland economy, which is highly dependent on fisheries (AMAP 2007). Such cultural services like recreation and aesthetical values would also be affected. Each of those services attracts more people to see the Ice sheet thus also bringing in more tourists. Water regulation as regulating ecosystem services could be altered through the large input of freshwater in the water cycle. The vast amount of "stored" water entering the water cycle within warmer climate would result in severe winter precipitation.
A new ecosystem service is possible as the thawing ice sheet will potentially form glacial freshwater lakes in Greenland. This will generate new recreation opportunities in summer – using lakes for different purposes from different social groups. Flora could expand deeper into Greenland and new species could be introduced as the climate warms giving the local population the chance to gain additional plant foods.
The potential options for preventing or reversing this potential regime shift mainly relates to the decrease of greenhouse gas input into the atmosphere at a global scale. This has to be achieved in order to prevent further climate warming leading to the loss of Greenland Ice Sheets. Options include reduction of deforestation, use of fossil fuels and charcoal as energy source, and cleaner economies. Geoengineering strategies has also been proposed, large scale experiments to decrease global temperature and CO2 concentration in the atmosphere. However, their applicability is debated and the usefulness is contested. As this system boundaries are set mainly around geophysical variables it is necessary to look at the social mechanisms involved to limit the influence on the main direct driver of greenhouse gas emissions. Nevertheless even if CO2 levels in atmosphere leads to atmospheric temperature increase, it is very hard to achieve from the local to regional management perspective. It does require global coordination and cooperation in order to achieve CO2 reduction targets.
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