NSIDC - "Because The Arctic Lost So Much Ice This Summer . . . Freeze-Up Will Begin Slowly

Figure 1: Sea ice extent for September 25, 2007



Current sea ice conditions: September 25, 2007

Figure 1 provides an updated map of sea ice extent for September 25, 2007; the magenta line shows the median September monthly extent based on data from 1979 to 2000. Sea ice extent is 4.20 million square kilometers (1.61 million square miles), an increase of 70,000 square kilometers (27,000 square miles) since the minimum extent of 4.13 million square kilometers (1.59 million square miles) on September 16. For more details on the minimum, please see the August 20 entry, below.

Figure 2: Summer melt season Arctic sea ice extent



Current sea ice conditions in context

Figure 2 is the updated time series of daily sea ice extent for 2007, which can be compared to the time series for 2005 and to the 1979 to 2000 average.

Now that freeze-up has begun, ice extent will continue to increase until it reaches its maximum sometime during March of next year. However, because the Arctic lost so much ice this summer, exposed open-water areas have absorbed a lot of solar energy; freeze-up will begin slowly, as you can see in Figure 2. Once the ocean waters cool to the freezing temperature, the rate of ice growth will accelerate. Nonetheless, the extreme loss of this summer’s sea ice cover and the slow onset of freeze-up portends lower than normal ice extent throughout autumn and winter, and the ice that grows back is likely to be fairly thin.

Much of our discussion to date covers the period since 1979, when consistent and reliable satellite observations began. However, considerable data exist for earlier years. One good source has been compiled by the United Kingdom’s Hadley Centre for Climate Prediction and Research. Their analysis, based primarily on ship reports and aircraft reconnaissance, takes the record back to the turn of the 20th century. Although the data quality prior to the early 1950s is debatable, no year in this century-long record comes close to matching what we have seen in 2007. This record also points to a significant persistent downward trend in summer sea ice extent over at least the past fifty years. September 2007 sea ice extent is nearly 50% lower than during the 1950s and 1960s

Figure 3: Arctic sea ice image on September 15–16, 2007



A closer look at sea ice extent around the minimum

Figure 3 shows a composite image from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) sensor for September 15–16, 2007, the period when we reached this year's minimum. Despite some cloud cover, you can see the ice edge (turquoise line) in many areas. The Northwest Passage, in the lower left corner, was largely open; the sea ice has since begun to form in earnest in many of the channels. Green lines indicate land masses; the purple line indicates the long-term median sea ice extent, and the dashed green line indicates the September 2005 sea ice edge.

The reason you see cone-like shapes, with the tips coalescing at the Pole, is that the MODIS sensor moves in swaths over the Arctic, and we have stitched these images together to form a composite image.

For more information on the Northwest Passage ice conditions, see the Canadian Ice Service Web site. The United States National Ice Center also tracks sea ice; visit them at the National Ice Center Web site

Figure 4: April to August 2007 monthly average sea ice drift



(Ed. - please see web site for animated content).
http://nsidc.org/news/press/2007_seaiceminimum/20070810_index.html

The role of sea ice drift

Another important aspect of this year’s extreme decline is the ice drift. As noted in earlier entries, persistent high pressure over the central Arctic Ocean led to fairly clear skies for the most of the summer, promoting melt. However, at the same time, the pattern of surface winds also led to an export of ice from the eastern Siberian side of the Arctic northward and westward. This is evident in Figure 4, which shows April through August monthly average ice motion calculated from NASA Advanced Microwave Scanning Radiometer (AMSR) imagery. It also helped push ice against the coast and offshore islands in Siberia, blocking the Northern Sea Route throughout the summer. Similar conditions in earlier years contributed to the loss of old ice that we discussed in our August 22 entry.

Impacts on people and wildlife

We cannot yet quantify the impacts of this year’s record low ice extent on indigenous communities and polar wildlife. However, this summer was likely difficult for polar bears and other wildlife that rely on the sea ice. Inhabitants of Arctic coastal communities have had to adjust to a lack of coastal ice for much of the summer, which has posed a significant challenge to their traditional methods of hunting and travel. While this year was particularly extreme, we are seeing a bold exclamation point on a trend of ice loss that has been ongoing for at least the past fifty years.

down wind. Living in the Lake Erie and LAke Ontario snow belts for over 30 years does that to you!

That much extra open water is going to have some effect on polar weather patterns. I don't see how it can be avoided.

as the climate has warmed. I think this will continue until finally one year it will rain all winter.