CRYSYS - CRYosphere SYStem in Canada

LEARN MORE ABOUT SEA ICE!

Sea ice covers between approximately 7.5 and 15.0 million kilometres² of the Arctic Ocean with an average thickness of about three metres. Maximum extent occurs at the end of March (see figure 1 below). At this time sea ice extends down the east coast of Canada to Newfoundland, covers most of the Gulf of St. Lawrence, all of Hudson Bay and the Canadian Archipelago. This vast area is remarkably efficient in reflecting winter/spring sunlight back into space and the presence of sea-ice helps to insulate the frigid atmosphere from the relatively warm ocean water. This prevents the ocean from significantly warming the atmosphere.

Figure 1: Mean sea ice extent in March (the month of average maximum extent). Source: Tom Agnew, MSC.

Minimum Arctic sea ice extent occurs in September of each year, the sea ice having shrunk back from almost all of Canadian coastal areas except for the high islands of the Canadian Archipelago. It remains contained within the Arctic Ocean and decreases to about 7.5 million km², which is about half the area at maximum extent (see figure 2 below)

Figure 2: Mean sea ice extent in September (the month of average minimum extent). Source: Tom Agnew, MSC.

Sea ice is such an efficient insulator that in its absence, the exposed ocean water would warm the overlying air by some 20 to 40°C (in winter). Due to its limited thickness, sea ice cover in the Northern Hemisphere is particularly sensitive to changes in temperature and ocean heat flux. In summer, any large reduction in sea ice cover will increase absorption of solar radiation at the ocean surface, thus increasing the air and ocean temperatures which will then further reduce sea ice cover. This is referred to as the sea ice albedo-temperature positive feedback. Global Climate Models suggest that about one third of the increase in global temperatures caused by increased greenhouse gases are a result of the thinning and shrinking sea ice cover in polar regions. Even small changes in the sea ice can result in large changes in the polar climate.

GLOBAL WARMING AND SEA ICE

Though scientists have been aware of the potential sensitivity of the climate system to changes in sea ice cover for many years, it has only been since the early 1970s that they have been able to regularly observe sea ice via satellite. During this interval of time, there has been a clear and steady decline in the extent of the Arctic sea-ice cover, showing it to be disappearing at a rate of approximately 3% each decade (see Figure 3 below). Even more startling is a reduction in sea ice thickness over the Arctic Ocean of 40% from a mean value of ~3.1 metres to 1.9 metres over the last 35 years. Despite this trend, there are exceptionally light ice years and heavy ice years in different locations reflecting the high year to year variability.

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Figure 3: Arctic sea ice extents anomalies (millions of km²) from 1979 to 1996.

At present, despite considerable uncertainties, global warming seems to be the most likely candidate driving these changes. Global climate models suggest that a general climate warming of a degree or two at lower latitudes will be amplified to a warming of several degrees at the poles. Sea ice changes are also remarkably consistent with model predictions given increases in atmospheric carbon dioxide.

If these changes are the result of increased greenhouse gases, then global climate models indicate that by the middle of this century summer sea ice will disappear over the Arctic Ocean and sea ice will only appear in winter.

• Sea Ice Codes and Terminology
• Canadian Ice Service - Visit the Education Corner and Resources
• Active and Passive Remote Sensing of Sea Ice
• Archive Sea Ice Motion Movies and Animations (January 1994 and June 1998)
• Current / Present Canadian Sea Ice Images and Animations on the SOCC website
• CRYSYS Photo Gallery: Lots of Sea Ice / Iceberg photographs.
• NSIDC Current Sea Ice Website

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