Figure 1. Arctic sea ice extent for November 2008 was 10.63 million square kilometers (4.10 million square miles). The magenta line shows the 1979 to 2000 average extent for November. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data.
—Credit: National Snow and Ice Data Center
High-resolution image

Overview of conditions

Average Arctic sea ice extent for the month of November was 10.63 million square kilometers (4.10 million square miles).

Ice extent for the month of November was 580,000 square kilometers (220,000 square miles) greater than November 2007 but 680,000 square kilometers (260,000 square miles) less than the 1979 to 2000 November average.

Figure 2. The graph above shows daily sea ice extent.The solid light blue line indicates 2008; the dashed green line shows 2007; and the solid gray line indicates average extent from 1979 to 2000. Sea Ice Index data.
—Credit: National Snow and Ice Data Center
High-resolution image

Conditions in context

The period of very rapid increase in ice extent that characterized October and early November has ended. The rise in ice extent through the remainder of November and early December has been much slower. The daily rate of ice growth has slowed simply because there is less physical room for ice to grow: the area of open water shrinks as ice fills it.

Figure 3. Air temperature anomalies for November 2008 at the 925 millibar level (roughly 1,000 meters [3,000 feet] above the surface) show unusually high temperatures over the Arctic Ocean. Areas in orange and red correspond to strong positive (warm) anomalies.
—Credit: From National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences Laboratory
High-resolution image

Unusually high air temperatures continue

Our November 10 post noted unusually high air temperatures over the Arctic Ocean, especially in the Beaufort Sea, from the minimum on September 14 through October 31. This high air temperature was because of heat transfer from the ocean to the atmosphere coming both from open water areas and from the release of latent heat associated with ice growth.

Air temperatures over the Arctic Ocean stayed warm through November, partly because of continued ocean-to-atmosphere heat transfer. However, some of the warmest anomalies were located well north of the open water areas seen in September. This regional pattern of warming points to the strong role of atmospheric circulation, pumping warm air into the region from the south.

Figure 4. 

Sea level pressure for November 2008 shows high- and low-pressure cells over the Arctic Ocean; strong winds have brought warmer-than-average air into the region. Regions of higher pressure are show in yellow and orange, regions of lower pressure are in purple.
—Credit: From National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences Laboratory
High-resolution image

 

Warm air from the south

Pressure differences between high- and low-pressure cells, in conjunction with the Coriolis force, result in winds that blow parallel to the pressure contours (Buys-Ballot’s Law). In November, winds between the high-pressure cell north of Alaska and the unusually low-pressure cell on the Atlantic side of the Arctic Ocean have brought warmer-than-average air into the region. This is consistent with the pattern of temperature anomalies shown in Figure 3.

For previous analysis, please see the drop-down menu under Archives in the right navigation at the top of this page.

NSIDC scientists provide Arctic Sea Ice News & Analysis, with partial support from NASA.

Figure 1. Arctic sea ice extent for October 2008 was 8.40 million square kilometers (3.24 million square miles). The magenta line shows the 1979 to 2000 average extent for October. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data.
—Credit: National Snow and Ice Data Center
High-resolution image

Overview of conditions

Sea ice extent for the month of October averaged 8.40 million square kilometers (3.24 million square miles). As of October 31, ice extent was at 9.27 million square kilometers (3.58 million square miles), more than doubling since the annual minimum of 4.52 million square kilometers (1.74 million square miles) measured on September 14, 2008.

October ice extent was 0.89 million square kilometers (0.34 million square miles) less than for the 1979 to 2000 average, but 1.63 million square kilometers (0.63 million square miles) greater than for October 2007.

Figure 2. The graph above shows daily sea ice extent.The solid light blue line indicates 2008; the dashed green line shows 2007; and the solid gray line indicates average extent from 1979 to 2000. Sea Ice Index data.
—Credit: National Snow and Ice Data Center
High-resolution image

Conditions in context

As autumn and winter take hold in the Arctic, sunlight wanes and days get shorter. The ice pack begins its annual growth cycle. The 2008 growth rate was especially strong in early October but subsequently slowed down slightly.

Figure 3. In this image, near-surface air temperatures show strong warming near the surface in the Beaufort sea region, an area with substantial open water at the end of the melt season. The anomalously high temperatures extend well up into the atmosphere, showing that the ocean is transferring heat to the atmosphere as ice forms. The vertical axis represents altitude measured by pressure, extending from the planet’s surface to 700 millibars (about 3,000 meters or 10,000 feet above sea level). The horizontal axis represents latitude from 50 degrees North (left) to 90 degrees North (right; North Pole).
—Credit: From National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences Laboratory
High-resolution image

Higher-than-average air temperatures

Over much of the Arctic, especially over the Arctic Ocean, air temperatures were unusually high. Near-surface air temperatures in the Beaufort Sea north of Alaska were more than 7 degrees Celsius (13 degrees Fahrenheit) above normal and the warming extended well into higher levels of the atmosphere. These warm conditions are consistent with rapid ice growth.

The freezing temperature of saline water is slightly lower than it is for fresh water, about –2 degrees Celsius (28 degrees Fahrenheit). While surface air temperatures in the Beaufort Sea region are well below freezing by late September, before sea ice can start to grow, the ocean must lose the heat it gained during the summer. One way the ocean does this is by transferring its heat to the atmosphere. This heat transfer is largely responsible for the anomalously high (but still below freezing) air temperatures over the Arctic Ocean seen in Figure 3. Only after the ocean loses its heat and cools to the freezing point, can ice begin to form. The process of ice formation also releases heat to the atmosphere.  Part of the anomalous temperature pattern seen in Figure 3 is an expression of this process, which is generally called the latent heat of fusion.

In the past five years, the Arctic has shown a pattern of strong low-level atmospheric warming over the Arctic Ocean in autumn because of heat loss from the ocean back to the atmosphere. Climate models project that this atmospheric warming, known as Arctic amplification, will become more prominent in coming decades and extend into the winter season. As larger expanses of open water are left at the end of each melt season, the ocean will continue to hand off heat to the atmosphere.

Figure 4. This animation of sea ice between September 1 and October 30 shows this year’s rapid ice regrowth. Data from AMSR-E sea ice concentration fields from the University of Bremen.
—Credit: From National Snow and Ice Data Center; data courtesy University of Bremen
Open animation in new window (.mov file, 884 KB)
(High-resolution animation available upon request)

Near-record October growth rates

As mentioned above, unusually high air temperatures go hand-in-hand with the rapid increase in ice extent seen through most of the month of October.

At its fastest point on October 15, the 2008 ice growth exceeded the 2007 growth rate on the same date by 92,000 square kilometers (36,000 square miles) per day. The near-record daily growth rate slowed toward the end of the month and has now fallen below the 2007 growth rate. It is important to reiterate this fast rate of growth is not unexpected under current conditions.

Record ice loss over the 2008 melt season

As discussed in our September 16, 2008, post, this year’s annual minimum represented the second-lowest point observed in the satellite record, surpassed only by the 2007 minimum. However, if we look at the total extent of ice lost between the March maximum and the September minimum, 2008 set a new record for total ice loss over an entire melt season. For more on the relatively high levels of ice that started the 2008 melt season and that led to this new record, see our April 7 post.

During the 2008 melt season, Arctic sea ice declined by 10.58 million square kilometers (4.08 million square miles). This was slightly more than the previous record for loss over an entire melt season, set in 2007, which was 10.51 million square kilometers (4.06 million square miles).

Arctic sea ice and climate are behaving in ways not seen before in the satellite record—both in the rate and extent of ice loss during the spring and summer, and in the record ice growth rates and increased Arctic air heating during the fall and winter.

Reference

Serreze, M. C. and J. A. Francis. 2006. The Arctic amplification debate. Climatic Change, 76, 241-264.

For previous analysis, please see the drop-down menu under Archives in the right navigation at the top of this page.

Figure 1. Daily Arctic sea ice extent for September 23, 2008, was 4.59 million square kilometers (1.77 million square miles). The orange line shows the 1979 to 2000 average extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data.
—Credit: National Snow and Ice Data Center
High-resolution image

Overview of conditions

Arctic sea ice extent on September 23, 2008, was 4.59 million square kilometers (1.77 million square miles), an increase of 77,000 square kilometers (30,000 square miles) above the minimum extent of 4.52 million square kilometers (1.74 million square miles) measured last week.

Figure 2. The graph above shows daily sea ice extent.The solid light blue line indicates 2008; the dashed green line shows 2007; and the solid gray line indicates average extent from 1979 to 2000. Sea Ice Index data.
—Credit: National Snow and Ice Data Center
High-resolution image

Conditions in context

Arctic sea ice extent, after reaching its seasonal minimum last week, has begun its annual cyclical increase in response to autumn cooling. The ice will grow over the cold, dark winter months and reach its maximum annual extent sometime next March.

During the intervening time, NSIDC will continue to provide updates on conditions. Also, note that as the season of ice growth progresses, NSIDC will slide the x-axis in Figure 2 to focus on the five-month window around the most current month. In our January entry, we will include a calendar-based full-year timeseries showing January 2008 through December 2008 extent compared to 2007 and to the 1979 to 2000 average.

Figure 3. Comparison of sea ice age during the second full week of September reveals that the Arctic will enter the winter ice growth season with less multiyear ice (bright colors), but far more first-year ice (dark blue) this year than it did in 2007. White indicates water; black indicates land.—Credit: From National Snow and Ice Data Center courtesy
C. Fowler, J. Maslanik, and S. Drobot, University of Colorado at Boulder
High-resolution image

 

High retention of first-year ice

Perhaps the most interesting aspect of the 2008 melt season was the higher-than-average retention of first-year sea ice (see earlier entries, including April 7).  Relatively thin first-year ice is more prone to melting out completely than older, thicker ice. However, more of this year’s first-year ice survived the melt season than is typical. Sea ice age maps from Sheldon Drobot, our colleague at the University of Colorado at Boulder, show that much more first-year ice survived in 2008 than in 2007. This is one of the reasons that 2008 did not break last year’s record-low minimum.

One cause of the high first-year ice survival rate was that this summer was cooler than in 2007. Lower temperatures slowed the melt rate in the early part of the season. While conditions in August favored rapid ice loss, they were not enough to make up for this early-season “cushion.” Furthermore, much of this year’s first-year ice was located at higher latitudes than in 2007, covering even the geographic North Pole. Regions that are far north have lower melt rates because they receive less solar energy than more southerly regions.

Figure 4. Ice motion in 2007 compacted the ice pack; in 2008, ice motion did not have this effect. Average August ice motion
captures the differences between the two years, with black arrows indicating ice motion. Sea ice motion derived using data from the NASA AMSR-E sensor.
—Credit: National Snow and Ice Data Center
High-resolution image

 

Dispersive sea ice motion

Sea ice motion also helps determine how the ice will fare each melt season. In 2007, a strong northward sea ice motion at the end of the melt season pushed ice floes together, compacting the ice. The tightly packed ice and high temperatures worked together to create a record-low extent.

This year, the wind patterns were different, leading to a less compacted ice cover. This, paired with slower summer melt, helped keep the overall extent larger.

For previous analysis, please see the drop-down menu under Archives in the right navigation at the top of this page.

Figure 1. Daily Arctic sea ice extent for September 12, 2008, was 4.52 million square kilometers (1.74 million square miles). The orange line shows the 1979 to 2000 average extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data.
—Credit: National Snow and Ice Data Center
High-resolution image

Overview of conditions

On September 12, 2008 sea ice extent dropped to 4.52 million square kilometers (1.74 million square miles). This appears to have been the lowest point of the year, as sea has now begun its annual cycle of growth in response to autumn cooling.

The 2008 minimum is the second-lowest recorded since 1979, and is 2.24 million square kilometers (0.86 million square miles) below the 1979 to 2000 average minimum.

Update 8:00 am MT October 2:

Final analysis indicates that the 2008 Arctic sea ice minimum occurred on September 14, 2008. For more information see the NSIDC press release: Arctic Sea Ice Down to Second-Lowest Extent; Likely Record-Low Volume.

 

Figure 2. The graph above shows daily sea ice extent.The solid light blue line indicates 2008; the dashed green line shows 2007; the dotted line shows 2005; the solid gray line indicates average extent from 1979 to 2000. Sea Ice Index data.
—Credit: National Snow and Ice Data Center
High-resolution image

Conditions in context

Despite overall cooler summer temperatures, the 2008 minimum extent is only 390,000 square kilometers (150,000 square miles), or 9.4%, more than the record-setting 2007 minimum. The 2008 minimum extent is 15.0% less than the next-lowest minimum extent set in 2005 and 33.1% less than the average minimum extent from 1979 to 2000.

This season further reinforces the long-term downward trend of sea ice extent.

Figure 3. Daily Arctic sea ice extent for September 12, 2008, the date of this year’s minimum (white) is overlaid on September 16, 2007, last year’s minimum extent (dark gray). Light gray shading indicates the region where ice occurred in both 2007 and 2008. Sea Ice Index data. About the data.
—Credit: National Snow and Ice Data Center
High-resolution image

Overlay of 2007 and 2008 at September minimum

The spatial pattern of the 2008 minimum extent was different than that of 2007. This year did not have the substantial ice loss in the central Arctic, north of the Chukchi and East Siberian Seas. However, 2008 showed greater loss in the Beaufort, Laptev, and Greenland Seas.

Unlike last year, this year saw the opening of the Northern Sea Route, the passage through the Arctic Ocean along the coast of Siberia. However, while the shallow Amundsen’s Northwest Passage opened in both years, the deeper Parry’s Channel of the Northwest Passage did not quite open in 2008.

A word of caution on calling the minimum

Determining with certainty when the minimum has occurred is difficult until the melt season has decisively ended. For example, in 2005, the time series began to level out in early September, prompting speculation that we had reached the minimum. However, the sea ice contracted later in the season, again reducing sea ice extent and causing a further drop in the absolute minimum.

We mention this now because the natural variability of the climate system has frequently been known to trick human efforts at forecasting the future. It is still possible that ice extent could fall again, slightly, because of either further melting or a contraction in the area of the pack due to the motion of the ice. However, we have now seen five days of gains in extent. Because of the variability of sea ice at this time of year, the National Snow and Ice Data Center determines the minimum using a five-day running mean value.

Ongoing analysis continues

We will continue to post analysis of sea ice conditions throughout the year, with frequency determined by sea ice conditions. Near-real-time images at upper right will continue to be updated every day.

In addition, NSIDC will issue a formal press release at the beginning of October with full analysis of the possible causes behind this year’s low ice conditions, particularly interesting aspects of the melt season, the set-up going into the important winter growth season ahead, and graphics comparing this year to the long-term record. At that time, we will also know what the monthly average September sea ice extent was in 2008—the measure scientists most often rely on for accurate analysis and comparison over the long-term.

Conditions in context

In a typical year, the daily rate of ice loss starts to slow in August as the Arctic begins to cool.  By contrast, in August 2008, the daily decline rate remained steadily downward and strong.

The average daily ice loss rate for August 2008 was 78,000 square kilometers per day (30,000 square miles per day). This is the fastest rate of daily ice loss that scientists have ever observed during a single August.  Losses were 15,000 square kilometers per day (5,800 square miles per day) faster than in August 2007, and 27,000 square kilometers per day (10,000 square miles per day) faster than average.

This August’s rapid ice loss reflects a thin sea ice cover that needed very little additional energy to melt out.

Figure 4. Sea surface temperature anomalies for August 2008, expressed with respect to 1982 to 2006 mean, correspond closely with ice retreat. Blue line indicates ice edge; warm colors indicate positive sea surface temperature anomalies.

To view both August 2007 and August 2008, click on the image.
—Credit: From National Snow and Ice Data Center courtesy Mike Steele and Wendy Ermold: Polar Science Center/Applied Physics Laboratory/University of Washington.

High-resolution image

Warm ocean temperatures

Mike Steele and Wendy Ermold from the University of Washington’s Applied Physics Laboratory Polar Science Center have been closely monitoring sea surface temperatures in the Arctic.

Positive sea surface temperature anomalies for August 2008 correspond with areas of ice retreat. When the ice melts, it exposes open water that absorbs solar energy; the warm ocean waters then favor further sea ice melt. An interesting phenomenon, in this regard, is that sea ice this August has been drifting into the Beaufort Sea only to melt when it encounters these warm ocean waters.

As autumn comes to the Arctic, the ocean will begin to lose its heat back to the atmosphere. This means that regions of high sea surface temperatures seen in August will be manifested as above-average air temperature in corresponding regions as autumn unfolds.

To view both August 2008 and 2007 sea surface temperature anomalies, click on Figure 4.

Figure 5. Monthly August ice extent for 1979 to 2008 shows 2008 as the second-lowest August on record.
—Credit: National Snow and Ice Data Center High-resolution image

 

August 2008 average extent compared to past Augusts

Arctic sea ice extent averaged over the month of August was 6.03 million square kilometers (2.33 million square miles). This is 1.64 million square kilometers (633,000 square miles) below the 1979 to 2000 August average,

However, August 2008 was still 670,000 square kilometers (260,000 square miles) above August 2007, despite the record-breaking rate of decline over the past month. Why would this be? The best explanation for this is that this summer did not experience the “perfect storm” of atmospheric conditions seen throughout the summer of 2007.

Even though August ice extent was above that of August 2007, the downward trend for August ice loss has now gone from -8.4% per decade to -8.7% per decade.

 

 

Figure 1. Daily Arctic sea ice extent for August 26, 2008, fell below the 2005 minimum, which was 5.32 million square kilometers (2.05 million square miles). The orange line shows the 1979 to 2000 average extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data.
—Credit: National Snow and Ice Data Center
High-resolution image

Overview of conditions

With several weeks left in the melt season, sea ice extent dipped below the 2005 minimum to stand as the second-lowest in the satellite record. The 2005 minimum, at 5.32 million square kilometers (2.05 million square miles), held the record-low minimum until last year.

Recent ice retreat primarily reflects melt in the Chukchi Sea off the Alaskan coast and the East Siberian Seas off the coast of eastern Russia.

Update 9:15 am MT August 27:

Arctic sea ice extent on August 26 was 5.26 million square kilometers (2.03 million square miles), a decline of 2.06million square kilometers (795,000 square miles) since the beginning of the month. Extent is now within 430,000 square kilometers (166,000 square miles) of last year’s value on the same date and is 1.97 million square kilometers (760,000 square miles) below the 1979 to 2000 average.

Figure 2. The graph above shows daily sea ice extent.The solid light blue line indicates 2008; the dark blue dotted line indicates 2005; the dashed green line shows extent for 2007; the gray line indicates average extent from 1979 to 2000. Sea Ice Index data.
—Credit: National Snow and Ice Data Center
High-resolution image

Conditions in context

Through the beginning of the melt season in May until early August, daily ice extent for 2008 closely tracked the values for 2005.

In early August of 2005, the decline began to slow; in August of 2008, the decline has remained steadily downward at a brisk pace. The 2005 minimum of 5.32 million square kilometers (2.05 million square miles) occurred on September 21.

Figure 1. Daily Arctic sea ice extent for August 24, 2008, was 5.47 million square kilometers (2.11 million square miles). The orange line shows the 1979 to 2000 average extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data.

—Credit: National Snow and Ice Data Center
High-resolution image

Overview of conditions

Arctic sea ice extent on August 24 was 5.47 million square kilometers (2.11 million square miles), a decline of 1.85 million square kilometers (714,000 square miles) since the beginning of the month. Extent is now within 580,000 square kilometers (220,000 square miles) of last year’s value on the same date and is 1.84 million square kilometers (710,000 square miles) below the 1979 to 2000 average.

Figure 2. Daily sea ice extent; the blue line indicates 2008; the gray line indicates extent from 1979 to 2000; the dotted green line shows extent for 2007. Sea Ice Index data.
—Credit: National Snow and Ice Data Center
High-resolution image

Conditions in context

Since our August 11 update, sea ice extent has declined at a fairly steady yet brisk pace. Since August 8, atmospheric circulation has settled into a pattern with high pressure covering most of the Beaufort, Chukchi, and East Siberian Seas. Recent ice losses have been most pronounced along the northern edge of eastern Siberia, which is consistent with generally southerly winds and above-average temperatures in this region.

Based on NASA Advanced Microwave Scanning Radiometer—Earth Observing System (AMSR-E) satellite images from the University of Bremen the wider, deeper Northwest Passage through the Parry Channel is almost open. The United States National Ice Center confirms that Amundsen’s Northwest Passage is navigable. The AMSR-E data furthermore indicate that the Northern Sea Route (also called the Northeast Passage) is open.

Last August, the Amundsen and Parry Channel routes both opened, but the Northern Sea Route remained blocked.

Animation provides a closer look at the melt

NSIDC has released new animations for Google Earth showing daily sea ice concentrations and extent in the Arctic. Click on the still image in Figure 3 to view a Quick Time animation of daily sea ice concentration over the past 90 days. Note the recent strong losses of ice north of Siberia.

Users who wish to manipulate the animation and access the daily updated animation may now download them from the NSIDC Virtual Globes page. Daily sea ice extent updates are automatically loaded into Google Earth so users always have the most recent files; 30-, 60-, and 90-day versions are available. To download the Google Earth files, learn more about Google Earth, or to find out how to read the time-slider tutorial, see http://nsidc.org/data/virtual_globes/.

Figure 4. Ice thickness measurements for summer 2008 indicate melt at the ice surface (red) versus the underside (yellow). This image shows changes in ice thickness at buoy locations (white circles), overlaid on the NSIDC sea ice concentration field for August 20. The numbers above each bar plot indicate total ice thickness at the beginning of the melt season compared to August 20.
—Credit: From National Snow and Ice Data Center courtesy D. Perovich, CRREL
High-resolution image

Changing ice thickness

As discussed in a number of previous postings (July 17, April 7), sea ice thickness is a key measure of the health of the sea ice. While the NASA ICESat sensor can give an overall picture of ice thickness over the Arctic Ocean, the most accurate way to measure ice thickness is by taking point measurements on the ground. Don Perovich, Jackie Richter-Menge, Bruce Elder, and Chris Polashenski at the United States Army Cold Regions Research and Engineering Laboratory track the evolution of sea ice thickness year round using autonomous buoys. The buoys are deployed as part of the North Pole Environmental Observatory, the Beaufort Gyre Observatory, and the DAMOCLES project. The buoy data have indicated increased amounts of melt on the underside of the ice cover in recent years; bottom melt last year was particularly extreme.

The pattern for 2008 has been more mixed. The ice at some buoy locations has thinned by more than a meter through the melt season because of strong melt both on the surface and the underside of the ice. Other locations show strong thinning caused by surface melt, while only modest thinning is apparent in others. Differences in surface melt from location to location reflect factors such as air temperature, the ice albedo, and cloud conditions. The wide range in bottom melt points to variations in the amount of ocean heat absorbed. In recent days, the buoys have indicated sub-freezing temperatures with surface melt coming to an end; however, bottom melt will continue for at least two to three more weeks and the ice extent decline, while slowing, will also continue.

Overview of conditions

Arctic sea ice extent on August 10 was 6.54 million square kilometers (2.52 million square miles), a decline of 1 million square kilometers (390,000 square miles) since the beginning of the month. Extent is now within 780,000 square kilometers (300,000 square miles) of last year’s value on the same date and is 1.50 million square kilometers (580,000 square miles) below the 1979 to 2000 average.

Conditions in context

Ice extent has begun to decline sharply. The decline rate surged to -113,000 square kilometers per day on August 7 and as of August 10 was -103,000 square kilometers per day. This compares to the long-term average decline of -76,000 square kilometers per day for this time of year. Normally, the peak decline rate is in early July.

Many of the areas now seeing a rapid retreat saw an early melt onset (see July 2, 2008); this helped set the stage for rapid retreat (July 17 and April 7). However, the more fundamental issue is that these regions started the melt season covered with thin first-year ice, which is especially vulnerable to melting out completely. Thin ice is also vulnerable to breakup by winds; the last ten days have seen a windy, stormy pattern that has accelerated the ice loss.

Figure 3. Sea-level pressure for August 8, 2008, shows a weather pattern favoring ice melt. Areas of high pressure are shown in yellow and red; areas of low pressure are shown in blue and purple.
—Credit: From National Snow and Ice Data Center courtesy Climate Diagnostic Center
High-resolution image

Storms trigger increased melt

A series of storms north of Alaska and Siberia in late July and early August have helped break up the thin ice and have brought warm southerly winds into the region.

Subsequently, a pattern has developed with high pressure over the Beaufort Sea and low pressure over the Laptev and East Siberian Seas (Figure 3). In accord with Buys Ballot’s Law, this pattern has brought southerly winds to the region, enhancing melt, breaking up ice, and pushing the ice edge northward.

Figure 4. Passive-microwave satellite data shows ice concentration on August 10, 2008, over the Northwest Passage region. The yellow line indicates Amundsen’s historic route through the passage. NASA AMSR-E data.
—Credit: From National Snow and Ice Data Center courtesy University of Bremen
High-resolution image

Opening of Amundsen’s Northwest Passage

The Northwest Passage that Roald Amundsen navigated with great difficulty starting in 1903 is opening for the second year in a row, as shown in the AMSR-E sea ice product from the University of Bremen (Figure 4).

The most recent operational analysis from the Canadian Ice Service and the U.S. National Ice Center on August 8 showed a small section of Amundsen’s historic path still blocked by a 50-kilometer (31-mile) stretch of sea ice, although that should melt within the next few days.

Amundsen’s route requires sailing through treacherous narrow and shallow channels, making it impractical for deep-draft commercial ships. The more important northern route, through the wide and deep Parry Channel, is still ice-clogged. The northern route opened in mid-August last year; it may still open up before the end of this year’s melt season.

For previous analysis, please see the drop-down menu under Archives in the right navigation at the top of this page.

Figure 1. Daily Arctic sea ice extent for July 31, 2008 was 7.71 million square kilometers (3.98 million square miles). The orange line shows the 1979-2000 average extent for that day. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

—Credit: National Snow and Ice Data Center
High-resolution image

Overview of conditions

Arctic sea ice extent on July 31 stood at 7.71 million square kilometers (2.98 million square miles). While extent was below the 1979 to 2000 average of 8.88 million square kilometers (3.43 million square miles), it was 0.89 million square kilometers (0.34 million square miles) above the value for July 31, 2007. As is normal for this time of year, melt is occurring throughout the Arctic, even at the North Pole.

 

Figure 2. Daily sea ice extent; the blue line indicates 2008; the gray line indicates extent from 1979 to 2000; the dotted green line shows extent for 2007. Sea Ice Index data.
—Credit: National Snow and Ice Data Center
High-resolution Image

Conditions in context

Sea ice extent continues to decline, but we have not yet seen last July’s period of accelerated decline. Part of the explanation is that temperatures were cooler in the last two weeks of July, especially north of Alaska.

Because we are past the summer solstice, the amount of potential solar energy reaching the surface is waning. The rate of decline should soon start to slow, reducing the likelihood of breaking last year’s record sea ice minimum.

Figure 3. Using average long-term decline rates is one way to project sea ice extent at the end of the 2008 season. The bottom dashed line shows decline rate one standard deviation faster than normal, the middle dashed line shows decline at average rates, and the top dashed line shows decline rate one standard deviation slower.
—Credit: National Snow and Ice Data Center
High-resolution image

Slower decline than 2007

To estimate the range of possibilities, we have used average long-term daily decline rates to project ice extent during the rest of the season (dashed blue lines). The bottom dashed line shows decline rate one standard deviation faster than normal, the middle dashed line shows decline at average rates, and the top dashed line shows decline rate one standard deviation slower.

If the Arctic experiences a normal decline rate, the minimum extent will be between the second-lowest extent, which occurred in 2005, and the third-lowest extent, which occurred in 2002. Even at a rate one standard deviation faster than normal, the extent will not fall below last year’s minimum—so it appears unlikely that we will set a new record low.

Figure 4. Passive-microwave satellite data shows ice concentration on July 31, 2008. Widespread areas of low concentration ice exist, shown in yellows. NASA AMSR-E data.

—Credit:From National Snow and Ice Data Center courtesy University of Bremen
High-resolution image

But a more vulnerable ice cover

Nevertheless, it is perhaps too soon to make a definitive pronouncement concerning this year’s probable extent at the summer minimum.  The Arctic sea ice is in a condition we have not seen since satellites began taking measurements. As discussed in our April analysis, thin first-year ice dominated the Arctic early in the melt season. Thin ice is much more vulnerable to melting completely during the summer; it seems likely that we will see a faster-than-normal rate of decline through the rest of the summer.

Building on our July 17 analysis, the fragility of the current ice conditions is evident in the sea ice concentration fields produced at the University of Bremen using NASA Advanced Microwave Sounding Radiometer (AMSR) data. Widespread areas of reduced ice concentration exist, particularly in the Beaufort Sea. Even north of 85 degrees latitude, pockets of much-reduced ice cover appear. The passive microwave data used in Figure 4 tends to underestimate ice concentration during summer because melt water on the surface of the ice can be mistaken for open water. Nevertheless, such low concentrations indicate strong melt and a broken, thin ice cover that is potentially vulnerable to rapid melt.

Figure 5.Visible-band satellite imagery confirms the low-concentration ice cover seen in Figure 4. This view places NASA MODIS Aqua data in a perspective generated in Google Earth, simulating a view from far above Earth.

—Credit: From National Snow and Ice Data Center courtesy NASA
High-resolution image

Visible imagery confirms weak ice cover

Visible-band imagery from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) sensor shows a more detailed picture of the ice than AMSR-E. Looking east into the Northwest Passage on July 28, the image confirms the low ice concentrations revealed in the AMSR-E data.

So, will we break last year’s record low minimum extent? Will the North Pole become ice-free? Probably not this year. However, the ice is in a vulnerable state and there are six weeks of melting left, so a lot can still happen.

And perhaps the most important point as we continue to watch this season’s evolving ice cover is that, whether or not Arctic sea ice sets a new record low, this year continues the pattern of well-below-average ice extent seen in recent years.

For previous analysis, please see the drop-down menu under Archives in the right navigation at the top of this page.