Sea Level and Ice

See also

International Polar Year: The State of Polar Research

An extract from:
A Statement from the International Council for Science/World Meteorological Organization Joint Committee for the International Polar Year 2007-2008

New assessments of the state of the Greenland and Antarctic ice sheets have been made using novel techniques. These include satellite measurements of changes to the elevation and the gravitational fields of the ice sheets, and estimates of the difference between snow input (from high-resolution meteorological models) and ice discharge (from satellite measurements of ice-sheet velocities and thickness at the coast). These assessments continue to be refined, but it now appears certain that both the Greenland and the Antarctic ice sheets are losing mass and thus raising sea level, and that the rate of ice loss from Greenland is growing. (See Figure 1.) Part of the loss is due to increased ice outflow, and the potential for these ice sheets to undergo further rapid ice discharge remains the largest unknown in projections of the rate of sea-level rise by the Intergovernmental Panel on Climate Change. New data also confirm that warming in the Antarctic is much more widespread than was thought prior to IPY. …

New evidence of the global warming rate also comes from other IPY projects. Data from robotic ocean-profiling floats, instrumented marine mammals and IPY research vessels confirm that the Southern Ocean, particularly the southern flank of the Antarctic Circumpolar Current, has warmed more rapidly than the global ocean average. In addition, the dense bottom water formed near Antarctica has freshened in some locations and warmed in others. The freshening is consistent with increased melt from the Antarctic ice shelves and ice sheet. These changes are signs that global warming is affecting the Antarctic in ways not previously suspected.

NOAA Arctic Report Card 2010

Return to previous Arctic conditions is unlikely
Record temperatures across Canadian Arctic and Greenland, a reduced summer sea ice cover, record snow cover decreases and links to some Northern Hemisphere weather support this conclusion

  • Atmosphere: Arctic climate is impacting mid-latitude weather, as seen in Winter 2009-2010
  • Sea Ice: Summer sea ice conditions for previous four years well below 1980s and 1990s
  • Biology: Rapid environmental change threatens to disrupt current natural cycles
  • Ocean: Upper ocean showing year-to-year variability without significant trends
  • Greenland: Record setting high temperatures, ice melt, and glacier area loss
  • Land: Low winter snow accumulation, warm spring temperatures lead to record low snow cover duration

Attribution of polar warming to human influence

Nature Geoscience 1, 750 – 754 (2008), Published online: 30 October 2008 | doi:10.1038/ngeo338

The polar regions have long been expected to warm strongly as a result of anthropogenic climate change, because of the positive feedbacks associated with melting ice and snow. Several studies have noted a rise in Arctic temperatures over recent decades, but have not formally attributed the changes to human influence, owing to sparse observations and large natural variability. Both warming and cooling trends have been observed in Antarctica, which the Intergovernmental Panel on Climate Change Fourth Assessment Report concludes is the only continent where anthropogenic temperature changes have not been detected so far, possibly as a result of insufficient observational coverage. Here we use an up-to-date gridded data set of land surface temperatures and simulations from four coupled climate models to assess the causes of the observed polar temperature changes. We find that the observed changes in Arctic and Antarctic temperatures are not consistent with internal climate variability or natural climate drivers alone, and are directly attributable to human influence. Our results demonstrate that human activities have already caused significant warming in both polar regions, with likely impacts on polar biology, indigenous communities, ice-sheet mass balance and global sea level.

Environment Canada: Canada’s Top Ten Weather Stories for 2008 – 2. The Great Arctic Thaw Continues

While news of this year’s ice loss in Arctic waters was not as stunning as last year, the trend to thinner and newer sea ice continued to surprise scientists around the world on many fronts:

  • On September 12, the sea ice extent in the Arctic Ocean dropped to 4.52 million square kilometres, coming close to last year’s record low of 4.13 million square kilometres. …
  • For August 2008, the rate of sea ice melt was the greatest ever. Satellite images showed ice declining at a rate of 84,686 square km per day in August, compared to 63,191 square km per day a year earlier.
  • In 2008, vast stretches of water in the western Arctic, including the Beaufort Sea, were almost clear of ice. …
  • Canadian Arctic waters had much less permanent ice compared to the same time last year. …
  • More stunning news in 2008 was the dramatic disappearance of nearly one-quarter of the massive, ancient ice shelves on Ellesmere Island. …
  • The calving of glaciers from Greenland led to nearly 1,000 icebergs off Canada’s east coast, more than in the previous four years combined. …
  • Also noteworthy, the ice extent in the Baltic Sea was the lowest since records began in 1720. Latvia and most of Finland had their warmest winter since 1925. Norway’s winter temperature was the second highest on record.

NSIDC – All About Sea Ice – Characteristics: Arctic vs. Antarctic

Sea ice differs between the Arctic and Antarctic, primarily because of their different geography. The Arctic is a semi-enclosed ocean, almost completely surrounded by land. As a result, the sea ice that forms in the Arctic is not as mobile as sea ice in the Antarctic. Although sea ice moves around the Arctic basin, it tends to stay in the cold Arctic waters. Floes are more prone to converge, or bump into each other, and pile up into thick ridges. These converging floes makes Arctic ice thicker. The presence of ridge ice and its longer life cycle leads to ice that stays frozen longer during the summer melt. So some Arctic sea ice remains through the summer and continues to grow the following autumn. Of the 15 million square kilometers (5.8 million square miles) of sea ice that exist during winter, on average, 7 million square kilometers (2.7 million square miles) remain at the end of the summer melt season.

The Antarctic is almost a geographic opposite of the Arctic, because Antarctica is a land mass surrounded by an ocean. The open ocean allows the forming sea ice to move more freely, resulting in higher drift speeds. However, Antarctic sea ice forms ridges much less often than sea ice in the Arctic. Also, because there is no land boundary to the north, the sea ice is free to float northward into warmer waters where it eventually melts. As a result, almost all of the sea ice that forms during the Antarctic winter melts during the summer. During the winter, up to 18 million square kilometers (6.9 million square miles) of ocean is covered by sea ice, but by the end of summer, only about 3 million square kilometers (1.1 million square miles) of sea ice remain.

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