Arctic Sea Melting Enhancing the Effect of Global Warming in High Latitudes The world warmed by about 0. 7°C in the 20th century. Every year in this century has been warmer than all but one in the last century (1998). If carbon-dioxide levels were magically to stabilize where they are now (almost 390 parts per million, 40% more than before the industrial revolution) the world would probably warm by a further half a degree or so as the ocean, which is slow to change its temperature, caught up. But CO2 levels continue to rise.
All this affect the ice pack in the Arctic. As temperature rises, ice melts. This causes many problems. A change to the reflectivity on the surface of the earth; which is called the albedo, affects the amount of solar radiation absorbed by the Earth. As Arctic sea ice continues to melt it exposes open water which is less reflective and causes the albedo to decrease. The reduction in albedo allows more light to be absorbed by the ocean. As the ocean water warms, more heat is added to the air creating a positive feedback and driving Arctic temperatures ever higher.
The reduction in sea ice is having a significant impact on arctic ecosystems. The Arctic sea is home to a wide variety of wildlife, including polar bears, arctic foxes, seals, walruses, and whales, fish species such as Arctic cod and char, and sea birds such as guillemots, auks, and eiders. Geoscientists all agree that the Arctic has been and will continue to be dramatically impacted by global warming and the other way around. A great amount of the surface in the Arctic is underlain by permanently frozen ground called “permafrost”. They highest layer experiences seasonal thawing.
Through research recent studies have shown that climatic warming my result in a 12 to 15% reduction in the area covered by permafrost and a 15 to 30% increases in the thickness of the active layer. As temperature rises permafrost melts, releasing stored carbon, but just as importantly, methane. Increased warming results in more permafrost melting pushing the earth system ever forward into a future enhanced greenhouse environment. When permafrost melts, water collects in small ponds on the surface increasing the heat gain nearly ten-fold.
The additional heat continues to melt the underlying permafrost causing it to collapse and increasing the size of the pond. This positive feedback further degrades the permafrost. As we know carbon dioxide makes up a greater proportion of the atmosphere by volume, but methane absorbs energy much more efficiently. Increased warming in the atmosphere from the arctic permafrost melting at high latitudes may cause an increase in the release of methane from bogs. Methane release from organic decomposition in wetlands coupled with carbon dioxide from melting permafrost will drive greenhouse gas levels higher, creating warmer temperatures.
It is likely that greenhouse-gas-induced Arctic warming is one of the major factors for the significant decline in sea ice area and thickness observed in many Arctic seas over the past few decades. General circulation computer models of the atmosphere project that greenhouse warming will occur more intensely over the Arctic in the future than any other part of the planet, largely because melting snow and ice will replace lighter surfaces with darker tundra and ocean surfaces, lowering the albedo, decreasing the sunlight reflected from the Arctic, and so accelerating the warming trend.
The warming observed so far over much of the Arctic land masses is only a small fraction of the intense 8-16 degree Celsius increase in winter temperatures projected by computer models if greenhouse gas levels double over the next few decades. What effect would a greenhouse gas doubling have on the Arctic ice pack? This is a difficult question because Arctic warming will have complex effects on air and ocean circulation, clouds and precipitation. Nevertheless, most computer models project a dramatic decline in Arctic sea ice.
The significance of the physical and chemical processes taking place in the Arctic region extends far outside it. The polar area has been described as a “refrigerator in the equator to pole transport of energy”. The NCAR model projects a 3. 8 degree Celsius global temperature increase for greenhouse gas doubling, near the high end of typical projections, in part because of shrinking Arctic sea ice. As well as being an area where nutrients are recycled and released into the water, the Polar Front region in the North Atlantic plays a fundamental role in the driving of ocean currents.
At the front near the Greenland, Iceland and Norwegian (GIN) seas and the Labrador Sea, warm salty water from the North Atlantic is cooled by Arctic waters and by intense heat loss to the atmosphere; it becomes denser and sinks to deeper layers of the ocean. Salt rejected as sea ice forms also increases the density and contributes to the process. Although a slow process, this sinking takes place over a wide area and each winter several million cubic kilometers of water sink and begin moving slowly south along the bottom of the Atlantic Ocean.
It is known as thermohaline circulation because it is driven in part by temperature and partly by salinity differences. The dense, cooled water becomes part of what is termed the Ocean Conveyor and the water eventually returns to the surface in the Indian and Pacific Oceans. As warm water returns to the Atlantic, the current moves pole wards as the Gulf Stream and North Atlantic Drift, warming northwestern Europe substantially. In addition, the formation of deep-water also dissolves carbon dioxide from the atmosphere and effectively removes it.
This is of significance in the global cycling of carbon. The Arctic region, therefore, plays a fundamental role in ocean circulation patterns, which in turn determine climate patterns over the rest of the globe. Unusually cold, fresh water has been increasing in the Labrador Sea in recent years. There are many possible expectations for this, including the GSA, which drifted into the Labrador Sea in the late 60’s and early 70’s, and the possible disappearance of sea ice bridges further north, allowing drifting and melting sea ice to enter the Davis Strait and the Labrador Sea from the north.
In every situation, a persistent freshening trend threatens the continued functioning of the Labrador Sea deep water formation. The Ocean Conveyor seems to have operated fairly reliably over the past several thousand years. However, after much research and examination of ice cores from both Greenland and Antarctica shows that this has not always been the case in the more distant past, and abrupt climatic changes associated with large amounts of sea ice in the North Atlantic and rapid changes in thermohaline circulation may have occurred repeatedly in the past.
Mathematical modeling suggests that a continuous freshwater source about twice the size of the GSA would be enough to permanently prevent deep water formation in both the GIN and Labrador Seas. Moreover, a continuous freshwater source only half the size of the GSA would be enough to shut down the Labrador deep water formation. But where could a continuous source of freshwater come from? For sure it’s not directly from melting sea ice. If enough of the 20 or 30 trillion cubic meters of Arctic sea ice were to melt each year to create a source twice the size of the GSA, the Arctic sea ice would be struggling after 10-15 years.
The Greenland ice sheet is about 100 times larger than the floating sea ice, and so it could contribute for a much longer period. In this case, the most likely source for increased freshwater in the far North Atlantic is increased precipitation. As the climate warms and the sea ice melts, many scientists expect that more rain and snow will fall on the Arctic Ocean and the North Atlantic, reducing the salinity and density of the water. But would this be enough to shut off thermohaline circulation?
Modelers Syukuro Manabe and Ronald J. Stouffer find that doubling greenhouse gas levels makes enough precipitation to cut thermohaline circulation in half, and then circulation recovers back to normal levels over several centuries. But if the levels quadruple, it is possible that emissions will increase unabated over the next century, causing thermohaline circulation to stop permanently. Using an easier model than Manabe and Stouffer, Thomas F.
Stocker and Andreas Schmittner find that a faster doubling of levels of greenhouse gases would shut the thermohaline circulation down permanently, however a slower doubling would only reduce the rate of circulation. The crazy part of this study is that Stocker and Schmittner’s “fast” scenario corresponds to current rates of greenhouse gas emission. Changes in precipitation are already beginning to occur. In Alaska, west of latitude 141, precipitation has increased by 30% between 1968 and 1990. Elsewhere precipitation in high latitudes has increased by 15% over the last 40 years.
Warming Arctic landmasses; declining sea ice area, extent and thickness; decreasing salinity; and major changes in Arctic and North Atlantic air and ocean circulation all form part of the picture. Impacts have already been observed on many scales: to Arctic ice algae and other micro-organisms, to walrus and polar bear populations and to Arctic human inhabitants, such as the Inuit. Long term climate records suggest that most of this warming, especially after 1920, is driven by increasing levels of human-created greenhouse gases in the atmosphere.
Computer modeling suggests that, if warming and levels of greenhouse gases continue to increase, most of the permanent ice pack is likely to melt and be replaced by seasonal winter ice. This Arctic meltdown would threaten the productivity of the Arctic Ocean and the continued existence of many Arctic animals, including walrus, many seal species, and polar bears. It would also threaten the traditional lifestyle of the Inuit, the indigenous inhabitants of the Arctic coast. The accelerated Arctic warming that would result from he removal of the permanent ice pack would significantly increase precipitation over the Arctic Ocean and far North Atlantic. This precipitation, combined with melt water from sea ice and the Greenland ice sheet, would reduce the salinity of the North Atlantic. Computer models suggest that these changes in salinity, especially if they happen quickly, may severely reduce or completely switch off the North Atlantic Conveyor, which is the major driving force for the Gulf Stream and global ocean circulation.
This may significantly cool the climate of northern Europe, and is likely to severely disrupt global marine life and fisheries, as well as reducing the ocean’s ability to remove greenhouse gases from the atmosphere and reduce the speed of global warming.
References http://archive. greenpeace. org/climate/arctic99/reports/seaice3. html http://www. economist. com/node/17575027/print http://www. economist. com/world/international/displaystory. cfm? story_id=17572735 http://www. uwsp. edu/geo/faculty/ritter/geog101/textbook/earth_system/Future_Geographies_Feedbacks. html