Page 127 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 4 atmosphere and Sur
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Melting Sea Ice Opens Arctic Shipping Lanes, However...
Sought for hundreds of years by explorers trying to navigate the icy waters of the arctic, the “north- west Passage” is a sea route connecting the atlantic and Pacific Oceans through the inland waterways of the Canadian archipelago. The northern Sea Route, also known as the “northeast Passage,” is another arctic sea route traversing the Russian coast and linking Europe and asia. These northern passages offer ships a shorter alternative to the long route through the Panama and Suez canals.
During most years, arctic Ocean sea ice blocked these sea routes, making them unavailable for shipping—that is, until recently. With a large ice melt in the summer of 2007, the northwest Pas- sage opened along its entire length for 36 days. in 2009, two German container ships completed the first commercial navigation of the northern Sea Route. Higher ocean and air temperatures asso- ciated with climate change cause the ice losses that opened these northern pas- sages. The 2012 summer sea-ice melt was the largest on record since 1979, allowing over 40 freighters and tankers to traverse the route (Figure Gn 4.1).
Albedo and Sea-Ice Melting in Chapter 1, we described the positive feedback loop between sunlight and the reflec- tivity of sea-ice surfaces. lighter sur- faces reflect sunlight and remain cooler, whereas darker surfaces absorb sunlight and heat up. Snow- and ice-covered sur- faces are natural reflectors; in fact, sea ice reflects about 80%–95% of the solar energy it receives. The ocean surface is darker, reflecting only an average of about 10% of insolation. This percent- age is albedo, or the reflective value of a surface. as the ice-covered area in the arctic retreats, darker water or land receives direct sunlight and absorbs more heat, which decreases albedo and adds to warming—a positive feedback.
Particulates from the atmosphere appear to decrease albedo even further. Scientists now have evidence that surface accumulations of black carbon (soot) and
▲Figure GN 4.1 Arctic summer sea-ice extent, 2012. [naSa/GSFC.]
other atmospheric particulates are signifi- cant causes of glacial snow and ice losses across the Himalayas. On the Greenland ice Sheet, black carbon accumulation from distant wildfires may be a major factor in the darkening of interior surfaces on the ice sheet.
Sea Ice and Arctic Shipping The pros- pect of an arctic Ocean with long ice- free periods for freighter and oil-tanker traffic is triggering commercial excite- ment. Use of the northern Sea Route is increasing: 4 vessels in 2010, 34 in 2011 (including a full-sized tanker), and
46 vessels in 2012. But while the arctic shipping lanes save time and money in the transport of goods, their use has potentially huge environmental costs—ice loss, climate impacts, oil spills, and risk of ship groundings. The stack emissions from new freighter and tanker traffic adds soot and particulate material into the arctic atmosphere. as this material settles on snow- covered glaciers and ice shelves, it darkens their surfaces and worsens albedo-reducing feedback loops that drive climate change.
Computer models now show that with continued significant losses of sea ice, the arctic Ocean could be ice-free during the summer within a decade. as shipping traffic increases, the ice– albedo positive feedback will acceler- ate through impacts of air pollution on surface albedos and surface energy budgets, the topics of Chapter 4.
geosystems now online GotoChapter4 on the MasteringGeography website (www.masteringgeography.com) for more maps and images regarding arctic sea ice and albedo feedback loops. For daily up- dates on the status of sea ice, go to the national Snow and ice Data Center website at nsidc.org/arcticseaicenews/. More im- ages of Greenland are at ocean.dmi.dk/ arctic/modis.uk.php.
▲Figure GN 4.2 Ship traffic and shipments in the Arctic Ocean. [Canadian Coast Guard.]
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0 500 1000 KILOMETRES
RUSSIA
Northern Sea Route
BERING SEA
ARCTIC OCEAN
Greenland
Baffin Bay
Northwest Passage
ALASKA (U.S.)
Sea-ice concentration (%)
0 50 100