The extended ice free season in the northwest passage and northern sea route, opens up the opportunity for shipping international cargo through the Arctic. This avoids the need for traversing either the Panama Canal or the Suez Canal and reduces shipping time. The Northern Sea Route is 7,400 kilometers shorter between South Korea and the Netherlands, than traveling via the Mediterranean Sea and the Suez Canal. Similarly, traveling from northwest Europe to Japan via the Northwest passage is 9,300 kilometers shorter than taking the Panama Canal route. These shortcuts, even if only available for a few months of the year, offer the opportunity for global shipping companies to save time and fuel in reaching their destinations. Many other opportunities will arise from an extended ice free season. Seasonal opening of these previously closed routes will also mean increased prospects for cruise tourism, and therefore new economic opportunities for Arctic communities. The availability of cheaper shipping may also lead to lower prices for imported goods that are currently prohibitively expensive, including food items. Mining and oil and gas companies may also take advantage of the open water season to exploit onshore and offshore resources that were previously too expensive to reach. Some of the opportunities of the longer ice free season may seem appealing, but they may come with a high price. Due to their formerly remote location, Arctic sea routes are often poorly mapped, with many underwater hazards to navigation. This makes the risk of a ship running aground and spilling its cargo or fuel potentially high. This risk increases greatly for offshore oil and gas exploration. Environmental resources for spill cleanup and mitigation are essentially absent throughout most of the Arctic region. Arctic ecosystems are extraordinarily sensitive to disruption due to often extreme conditions. Under the pressures of climate warming, an unchecked oil or gas spill, even of relatively minor extent, can have devastating consequences. The 1989 Exxon Valdez oil spill in southern Alaska, USA, covered 2,100 kilometers of coastline and 28,000 square kilometers of ocean. Some oil still remains in the sand and soil, and continues to have severe consequences for the entire ecosystem. As of 2014, some species have not recovered to their pre-spill populations. In the Arctic, the impact would be far worse. In particular, any such disaster could affect marine and terrestrial animal populations often used in subsistence hunting and fishing in indigenous communities. In addition to economic benefits and risks, the reduction of sea ice, particularly in summer, has important physical impacts for arctic coastal communities. What might some of these issues be? A, coastal erosion due to increased wave action. B, availability of new fish species due to warmer, more open water. C, increased opportunity for local Arctic boat travel. D, new opportunities for leisure swimming. More than one answer might be correct, so check all that you think apply. The reduction of sea ice will increase wave action, causing coastal erosion. So A is correct. Both B and C are also correct, as there will be movement of fish species due to the warmer, more open water, and the open water also will increase the opportunity for local travel by boat. The water, although open, will not be warm enough for leisure swimming. Therefore, D is incorrect. Let's now explore the impact of sea ice reduction on Arctic coastal communities. In the past, many communities experienced a short ice freeze season, where the edge of the pack ice would remain no more than several tens of kilometers away. Today, many of the same communities experience ice-free seasons that last many months of the year, where packed ice retreats several hundred kilometers. For the hunters in these communities, it is now more difficult to get near and onto the sea ice. Once on the ice, hunters may face unpredictable ice conditions with an increased risk of getting trapped once on the ice. Additionally, the changing sea ice regime also means that navigating these waters is risky. Boaters are at risk to life and limb because the ice is able to drift and move around much more. Where the pack ice edge now retreats far from shore, the formerly protected shorelines are exposed and vulnerable to erosion by powerful waves from the open ocean. Where coastal regions are underlain by easily melted ice ridge permafrost, this problem becomes much more severe. For example, along Canada's Beaufort sea coast, ice rich coastlines have been measured to retreat at rates up to five meters per year. Arctic communities are often located near the coast due to the availability of marine food sources and the logistics of keeping them supplied. Coastal erosion in some communities such as Tuktoyaktuk, Canada, along the Beaufort Sea, means that the community needs to retreat inland or even to relocate at great expense as the sea encroaches on built up areas. The moving costs of relocating the island village of Kivalina in Alaska, with a population of about 400 people, have been estimated at more than $95 million. In addition to the impacts caused by melting sea ice, land-based ice such as glaciers, ice caps, and ice sheets have also been in decline since the beginning of industrialization. Based on what you learned in lesson two, what are some of the primary impacts of this decline in land-based ice on the ocean? A, Increasing ocean acidification by adding water to the oceans. B, raising sea level by adding water to the oceans. C, increasing ocean salinities by adding water to the oceans. D, changing ocean circulation through modifying ocean density. More than one answer might be correct, so check all that you think apply. Answers B and D are both true. As land-based ice melts, water is added to the oceans. This causes ocean circulation to change as well as raising sea level. Although the oceans are becoming more acidic, it's not primarily a function of glacial melt. So A is incorrect. Finally, ocean salinities are decreasing with the addition of fresh water, so C is also incorrect. We will now discuss these impacts in further detail. As we learned in lesson three, most of the fresh water on Earth is locked up in polar ice on land. This is predominantly in the major ice sheets found in Antarctica and Greenland. They collectively cover about 15.7 million square kilometers and have a combined volume of over 30 million cubic kilometers of ice. Any melting of this ice introduces fresh water to the ocean, which in turn raises global sea level. The west Antarctic and Greenland ice sheets have experienced significant calving and melting, respectively, over the past few decades. The Greenland ice sheet has lost on average 121 gigatons of ice per year between 1993 and 2010. This is the equivalent of a 0.33 millimeter per year rise in global sea level. This figure almost doubled between 2005 and 2010, when the ice loss reached 229 gigatons per year. Losses were projected to continue to increase in the near future. Smaller glaciers found in the Russian Arctic have similarly lost around 11 gigatons of ice per year, between 2003 and 2009. On the whole, melting glaciers and ice sheets create risks for low lying communities in the Arctic and world wide. Sea level does not just rise as additional water is added from melting ice sheets and glaciers. It is also driven by the changes in density of seawater as salinity and temperature evolve. This means that the additional fresh water being added to our oceans has a more complex impact on sea level. This process sets the steric sea level. Based on what you learned about seawater density in lesson two, how might warming ocean waters lead to an increase in sea level? A, increasing the temperature decreases the density of seawater and thus decreases the volume. B, increasing the temperature decreases the density of seawater and thus increases the volume. C, increasing the temperature increases the density of seawater and thus increases the volume. Or D, increasing the temperature increases the density of seawater and thus decreases the volume. Answer B is correct. Warmer water is less dense, therefore, for a constant mass of water, density and volume are inversely related. Decreasing the density increases the volume, and thus pushes up the sea level, since the ocean bottom is effectively fixed. This heat driven expansion is referred to as thermal expansion. Thermal expansion can be an effective way to raise the sea level of the global ocean. Its impact varies, though, as it depends on how heat is distributed throughout the ocean. Although lowering salinity has a similar effect in principle, the limited variations of salinity in the ocean mean the addition of fresh melt water will not play a significant role in driving changes in the global main steric sea level. This is because both thermal expansion and melting glacial ice are ultimately driven by climate. Thermal expansion and melting glacial ice can alter sea level over the long term, from decades to centuries. Sea level can also be changed in the short term through tides, storms and seasonal temperature changes. But steric sea level change and terrestrial ice changes explain 75% of the sea level change observed since 1971. Steric sea level, on average, rose by 0.8 millimeters per year between 1971 and 1993. This increased to 1 millimeter per year between 1993 and 2010. These figures are projected to rise in the future, in proportion to enhanced ocean warming. Sea level rise due to melting glacier ice, however, will not be uniformly felt throughout the global ocean. Worldwide, approximately 400 million people live within 20 meters of sea level, and within 20 kilometers of a coast. These populations would be directly affected by sea level rise. This means that glacier melting in remote polar locations, far removed from most of the world's populations, have global consequences that are not confined to polar regions. In particular, some island nations, for example, Tonga, the Maldives, and the Cook Islands, are only a few meters above present sea level. This makes them particularly vulnerable to rising sea level. Sea level rise effects include beach erosion, and the loss of vital agricultural and cultural resources. But the most important effect is the inundation of coastal land and the eventual displacement of millions of people. The figure of 3.2 millimeters per year of average sea level rise is a global average. So some areas will be more affected than others. Estimates like the ones we've discussed in this lesson often do not take ice sheet collapse into account. Multiple researchers have concluded that the collapse of the West Antarctic Ice Sheet has already begun. This is estimated to add 1.2 to 3.6 meters to current sea level over the course of the next few hundred years. Once started, ice sheet collapses like dominoes tipping over, and that once started, it is essentially unstoppable. The melting of ice sheets and glaciers may have other profound consequences for our oceans. In particular, the inflow of fresh water will change the ocean's salinity, impacting the density structure. From what you learned in lesson two, how do you think this fresh water input may impact the Global Thermohaline Circulation? A, by lowering salinity and density, deep water formation may be enhanced, driving a stronger thermohaline circulation. B, by lowering salinity and density, deep water formation may be enhanced, driving a weaker thermohaline circulation. C, by lowering salinity and density, deep water formation may be decreased, driving a stronger thermohaline circulation. D, by lowering salinity and density, deep water formation may be decreased, driving a weaker thermohaline circulation. Answer D is the correct response. By lowering salinity and density, deep water formation may be decreased. This is because the same winter cooling may no longer be sufficient to make the surface density high enough for waters to sink to depth. This could impact the formation of North Atlantic deep water, a key driver of the thermohaline circulation. The importance of this is that the ocean conveyor transports large amounts of warm water to the North Atlantic region.
