Monthly Archives: September 2015

Arctic sea ice reaches fourth lowest minimum

On September 11, Arctic sea ice reached its likely minimum extent for 2015. The minimum ice extent was the fourth lowest in the satellite record, and reinforces the long-term downward trend in Arctic ice extent. Sea ice extent will now begin its seasonal increase through autumn and winter. In the Antarctic, sea ice extent is average, a substantial contrast with recent years when Antarctic winter extents reached record high levels.

Please note that this is a preliminary announcement. Changing winds or late-season melt could still reduce the Arctic ice extent, as happened in 2005 and 2010. NSIDC scientists will release a full analysis of the Arctic melt season, and discuss the Antarctic winter sea ice growth, in early October.

Overview of conditions

Figure 1. Arctic sea ice extent for September 11, 2015 was 4.41 million square kilometers (1.70 million square miles). The orange line shows the 1981 to 2010 average extent for the 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

Figure 1. Arctic sea ice extent for September 11, 2015, was 4.41 million square kilometers (1.70 million square miles). The orange line shows the 1981 to 2010 average extent for the 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

On September 11, 2015, sea ice extent dropped to 4.41 million square kilometers (1.70 million square miles), the fourth lowest minimum in the satellite record. This appears to be the lowest extent of the year. In response to the setting sun and falling temperatures, ice extent will now climb through autumn and winter. However, a shift in wind patterns or a period of late season melt could still push the ice extent lower.

The minimum extent was reached four days earlier than the 1981 to 2010 average minimum date of September 15. The extent ranked behind 2012 (lowest), 2007 (second lowest), and 2011 (third lowest). Moreover, the nine lowest extents in the satellite era have all occurred in the last nine years.

Both the Northern Sea Route, along the coast of Russia, and Roald Amundsen’s route through the Northwest Passage are open. How long they remain open depends on weather patterns and the amount of heat still present in the ocean mixed layer (about the top 50 feet of the ocean). The deeper and wider Northwest Passage route through Parry Channel, which consists of M’Clure Strait, Barrow Strait, and Lancaster Sound, still has some ice in it.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of September 14, 2015, along with daily ice extent data for last year and the three lowest ice extent years (2012, 2007, and 2011).

Figure 2a. The graph above shows Arctic sea ice extent as of September 14, 2015, along with daily ice extent data for last year and the three lowest ice extent years (2012, 2007, and 2011). 2015 is shown in blue, 2014 in green, 2012 in orange, 2011 in brown, and 2007 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data. About the data

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

This year’s minimum was 1.02 million square kilometers (394,000 square miles) above the record minimum extent in the satellite era, which occurred on September 17, 2012, and 1.81 million square kilometers (699,000 square miles) below the 1981 to 2010 average minimum.

Figure 2b. This figure shows patterns of sea level pressure and air temperature at the 925 hPa level for the summers (June through August) of 2015 and for 2007, expressed as differences with respect to average conditions over the period 1981 to 2010.

Figure 2b. This figure shows patterns of sea level pressure and air temperature at the 925 hPa level for the summers (June through August) of 2015 and for 2007, expressed as differences from the 1981 to 2010 average. The patterns for 2015 contributed to low September extent, but were not as favorable for producing low extent as the patterns seen in 2007.

Credit: NOAA/ESRL Physical Sciences Division
High-resolution image

Research has shown that especially low September sea extent tends to occur in years when the summer atmospheric circulation over the central Arctic Ocean is dominated by high atmospheric pressure, or anticyclonic conditions. This is because anticyclonic conditions tend to bring relatively sunny and warm conditions, and a clockwise wind pattern promotes ice convergence, making for a more compact, and thus smaller ice cover. The best example of this pattern occurred during the summer of 2007, which had the second lowest September extent in the satellite record. Conversely, Septembers with high extent tend to occur when the atmospheric circulation over the central Arctic Ocean is more cyclonic (counterclockwise), meaning unusually low pressure at the surface. This pattern brings more clouds, lower temperatures, and winds that spread the ice over a larger area.

Viewed in this framework, the pattern of atmospheric circulation for summer 2015 as a whole (June through August) favored a low September extent. Sea level pressures were higher than average over the central Arctic Ocean, as well as over Greenland and the surrounding region. Pressures were below average over north-central Eurasia. This was associated with air temperatures at the 925 hPa level (about 3,000 feet above the surface) that were above average over much of the Arctic Ocean, especially along the coast of eastern Siberia, in the Laptev Sea, and the Canadian Arctic Archipelago extending to the pole. However, it was not nearly as favorable as the 2007 pattern, when the area of unusually high pressure was located further south and east (over the northern Beaufort Sea), and unusually low pressure extended along much of the coast of northern Eurasia. This led to a pattern of warm winds from the south over the East Siberian and Chukchi Seas, promoting strong melt and transport of ice away from the coast. For both 2015 and 2007, the summer pressure patterns led to winds directed down the Fram Strait, helping to transport ice out of the Arctic Ocean into the East Greenland Sea.

Varying distribution of ice in 2015 versus 2012

Figure 3. This image compares differences in ice-covered areas between September 11, 2015 and September 17, 2012, the record low minimum extent.

Figure 3. This image compares differences in ice-covered areas between September 11, 2015 and September 17, 2012, the record low minimum extent. Light blue shading indicates the region where ice occurred in both 2015 and 2012, while white and medium blue areas show ice cover unique to 2012 and to 2015, respectively. Sea Ice Index data. About the data

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

While minimum extent was higher this year compared to 2012, there are many similarities in the spatial pattern of the ice cover. Both years had considerable ice loss in the Beaufort, Chukchi, and East Siberian seas, though this year the ice extent did not retreat as far north as in 2012. Both also show a tongue of ice extending further southward on the Siberian side of the Arctic. In 2012, the tongue extended toward the Laptev Sea. This year, the tongue is farther east, in the western part of the East Siberian Sea, and is related to thicker, older ice that did not melt completely. North of Svalbard and in the Kara Sea, sea ice extent was slightly higher this year than in 2012.

Previous minimum Arctic sea ice extents

Table 1.   Previous minimum Arctic sea ice extents
 YEAR MINIMUM ICE EXTENT DATE
IN MILLIONS OF SQUARE KILOMETERS IN MILLIONS OF SQUARE MILES
2006 5.77 2.28 September 17
2007 4.15 1.60 September 18
2008 4.59 1.77 September 20
2009 5.12 1.98 September 13
2010 4.61 1.78 September 21
2011 4.34 1.67 September 11
2012 3.39 1.31 September 17
2013 5.05 1.95 September 13
2014 5.03 1.94 September 17
2015 4.41 1.70 September 11
1979 to 2000 average 6.70 2.59 September 13
1981 to 2010 average 6.22 2.40 September 15

Ten lowest minimum Arctic sea ice extents (1981 to 2010 average)

Table 2.  Ten lowest minimum Arctic sea ice extents (1981 to 2010 average)
 RANK  YEAR MINIMUM ICE EXTENT DATE
IN MILLIONS OF SQUARE KILOMETERS IN MILLIONS OF SQUARE MILES
1 2012 3.39 1.31 September 17
2 2007 4.15 1.60 September 18
3 2011 4.34 1.67 September 11
4 2015 4.41 1.70 September 11
5 2008 4.59 1.77 September 20
6 2010 4.61 1.78 September 21
7 2014 5.03 1.94 September 17
8 2013 5.05 1.95 September 13
9 2009 5.12 1.98 September 13
10 2005 5.32 2.05 September 22

Note that the dates and extents of the minima have been re-calculated from what we posted in previous years. In March 2015, NSIDC made two revisions to Arctic Sea Ice Index extent values used in our analyses, to improve scientific accuracy. These changes do not significantly affect sea ice trends and year-to-year comparisons, but in some instances users may notice very small changes in values from the previous version of the data. First, calculations of ice extent near the North Pole were improved whenever a newer satellite orbited closer to the pole than older satellites in the series, by using a sensor-specific pole hole for the extent calculations. Second, the accuracy of ice detection near the ice edge was slightly improved by adopting an improved residual weather effect filter. Details on the changes are discussed in the Sea Ice Index documentation.

U.S. icebreaker reaches the North Pole

Figure 4. Scientists and the crew of U.S. Coast Guard Icebreaker Healy have their portrait taken at the North Pole on September 7, 2015.

Figure 4. Scientists and the crew of U.S. Coast Guard Icebreaker Healy have their portrait taken at the North Pole on September 7, 2015. The Healy reached the pole on September 5.

Credit: U.S. Coast Guard photo by Petty Officer 2nd Class Cory J. Mendenhall
High-resolution image

After four weeks at sea, the Coast Guard Icebreaker Healy reached the North Pole on September 5. The ship left Dutch Harbor on August 9 with about 145 people on board, including about fifty scientists. The Healy is a medium-duty icebreaker and in the years past would not have been suitable to navigate through thick ice floes to reach the pole. This is the first time that a U.S. ship has made a solo traverse of the North Pole. As clear evidence that the melt season was coming to a close, air temperatures were 21 degrees Fahrenheit (-6 degrees Celsius). The U.S. icebreaker’s capability is far behind that of Russia and other Arctic nations, and plans are ongoing for the U.S. to build a new polar-class icebreaking vessel.

Impact of sea ice convergence in 2013

Figure 5. These graphs show onshore ice drift during the summer of 2013.

Figure 5. These graphs show onshore ice drift during the summer of 2013. Due to ice convergence, an ice area in May (in red) is compressed by ~23% by the end of the summer (dashed line).

Credit: Ron Kwok, NASA Jet Propulsion Laboratory
High-resolution image

Thick, deformed ice, made up of pressure ridges with deep keels, is formed when the sea ice cover is pushed against or converges on the coast. Sea ice convergence along the coasts of Greenland and the Canadian Arctic Archipelago is a source of the thickest ice (tens of meters) in the Arctic Ocean. The thicker ice is more likely to survive the summer to form the Arctic Ocean’s perennial ice cover. A new paper by Ron Kwok at the NASA Jet Propulsion Laboratory shows that in summer of 2013, strong wind-driven onshore ice drift was forced by the relative location of high- and low- pressure centers over the Arctic Ocean (see Figure 5). A sampled ice parcel (in red) shows an area compression of 23% between May and October; the dashes indicate its area by end of summer. This is equivalent to an increase in thickness of ~30% within that area. If this thicker ice were transported to areas of high melt rates (like that in the southern Beaufort), it would have an impact on summer ice coverage. The presence of a band of sea ice that survived a large part of the summer in 2015, is likely due to the thicker ice that formed in this region.

Reference

Kwok, R. 2015. Sea ice convergence along the Arctic coasts of Greenland and the Canadian Arctic Archipelago: Variability and extremes (1992–2014). Geophysical Research Letters, (Accepted) doi:10.1002/2015GL065462.

Steady decline, seasonal minimum approaching

August saw a remarkably steady decline in Arctic sea ice extent, at a rate slightly faster than the long-term average. Forecasts show that this year’s minimum sea ice extent, which typically occurs in mid to late September, is likely to be the third or fourth lowest in the satellite record. All four of the lowest extents have occurred since 2007. In mid-August, Antarctic sea ice extent began to trend below the 1981 to 2010 average for the first time since November 2011.

Overview of conditions

sea ice extent map

Figure 1. Arctic sea ice extent for August 2015 was 5.61 million square kilometers (2.16 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. 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

Average sea ice extent for August 2015 was 5.61 million square kilometers (2.16 million square miles), the fourth lowest August extent in the satellite record. This is 1.61 million square kilometers (621,000 square miles) below the 1981 to 2010 average for the month, and 900,000 square kilometers (350,000 square miles) above the record low for August, set in 2012.

The rapid pace of daily ice loss seen in late July 2015 slowed somewhat in August. The pace increased slightly toward the end of the month, so that by August 31 Arctic sea ice extent was only slightly greater than on the same date in 2007 and 2011. The ice is currently tracking lower than two standard deviations below the 1981 to 2010 long-term average.

Sea ice extent remains below average in nearly every sector except for Baffin Bay and Hudson Bay, where some ice persists in sheltered coastal areas. A striking feature of the late 2015 melt season are the extensive regions of low-concentration ice (less than 70% ice cover) in the Beaufort Sea. A few patches of multi-year sea ice surrounded by open water remain in the central Beaufort Sea.

Conditions in context

sea ice extent graph

Figure 2. The graph above shows Arctic sea ice extent as of August 31, 2015, along with daily ice extent data for four previous years. 2015 is shown in blue, 2014 in green, 2013 in orange, 2012 in brown, and 2011 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

Ice loss rates were quite steady through most of the month of August. Sea ice loss for August averaged 75,100 square kilometers per day (29,000 square miles), compared to the long-term 1981 to 2010 average value of 57,300 square kilometers per day (22,100 square miles per day), and a rate of 89,500 square kilometers per day for 2012 (34,500 square miles per day).

Cool conditions prevailed in the East Siberian, Chukchi, and western Beaufort seas, where air temperatures at the 925 millibar level were 1.5 to 2.5 degrees Celsius (3 to 5 degrees Fahrenheit) below average. However, a broad region of higher-than-average temperatures extended from Norway to the North Pole, 1.5 to 2.5 degrees Celsius (3 to 5 degrees Fahrenheit) above average. Sea level pressures were up to 10 millibars above average over the central Arctic Ocean, paired with slightly below average values in north-central Siberia, similar to the dipole-like pattern seen for July. The Arctic Oscillation was in its negative phase for most of the month, again similar to July.

August 2015 compared to previous years

trend graph

Figure 3. Monthly August ice extent for 1979 to 2015 shows a decline of 10.3% per decade.

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

Arctic sea ice extent averaged for August 2015 was the fourth lowest in the satellite data record. Through 2015, the linear rate of decline for August extent is 10.3% per decade.

 

Forecasting the minimum

||Credit: RESEARCHER'S NAME/ORGANIZATION *or * National Snow and Ice Data Center| High-resolution image

Figure 4. The graph shows ice extent forecasts, based on ice extent as observed on August 31, 2015 and past years’ observed rates for selected years.

Credit: W. Meier, NASA Goddard Cryospheric Sciences Lab
High-resolution image

One way of estimating the upcoming seasonal minimum in ice extent is to extrapolate from the current extent, using previous years’ rates of daily sea ice loss. Assuming that past years’ daily rates of change indicate the range of ice loss that can be expected this year, this method gives an envelope of possible minimum extents for the September seasonal minimum. However, it is possible to have unprecedented loss rates, either slow or fast.

Starting with the ice extent observed on August 31 and then applying 2006 loss rates, the slowest rate in recent years, results in the highest extrapolated minimum for 2015 of 4.50 million square kilometers (1.74 million square miles), and a September monthly average extent of 4.59 million square kilometers (1.77 million square miles). The lowest daily minimum comes from using the 2010 pace, yielding an estimated 4.12 million square kilometers (1.67 million square miles) for the daily minimum, and a September monthly average extent of 4.33 million square kilometers (1.67 million square miles).

Using an average rate of ice loss from the most recent ten years gives a one-day minimum extent of 4.38 ± 0.11 million square kilometers (1.79 million square miles), and a September monthly average of 4.49 ± 0.09. As of August 31, the 5-day running daily average extent is 4.72 million square kilometers. If no further retreat occurred, 2015 would already be the sixth lowest daily ice extent in the satellite record.

The forecast places the upcoming daily sea ice minimum between third and fourth lowest, with fourth more likely. There is still a possibility that 2015 extent will be lower than 4.3 million square kilometers, the third lowest sea ice extent, surpassing the 2011 sea ice extent minimum, and a small chance of surpassing 2007, resulting in the second-lowest daily minimum. This assumes that we continue to have sea ice loss rates at least as fast as those of 2010. This was indeed the case for the final ten days of August 2015.

Northwest Passage icy; Northern Sea Route remains open

Figure 5. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque et condimentum nunc. Maecenas tempor cursus fermentum. Donec nulla quam, commodo eu urna nec, aliquet accumsan lorem. Mauris justo orci, sollicitudin quis diam vel, vehicula mollis diam. Donec sollicitudin nisi vel blandit gravida..||Credit: RESEARCHER'S NAME/ORGANIZATION *or * National Snow and Ice Data Center| High-resolution image

Figure 5. Click on the image to view an animation of sea ice concentration north of Canada for August 23 to September 1, 2015.

Credit: Canadian Ice Service Daily and Regional Ice Charts
High-resolution image

The southerly route through the Northwest Passage is open. The passage was discovered during 1903 to 1906 by Roald Amundsen, who made the first transit of the passage from Baffin Bay to the Beaufort Sea. This route passes south of Prince of Wales Island and Victoria Island before entering the Beaufort Sea south of Banks Island. Data from the AMSR-2 satellite, which uses passive microwave emission, suggests that this path is ice-free. The higher-resolution Multisensor Analyzed Sea Ice Extent (MASIE) product, based on several data sources and human interpretation, shows only a few areas of low-concentration ice. The broader and deeper passage through the Canadian Arctic Archipelago, between Lancaster Sound, Parry Channel, and McClure Strait, is still obstructed by ice, but at the end of August ice blocked only a short portion near Victoria Island. Before drawing conclusions about navigability, however, it is important to check with the operational services such as the National Ice Center (NIC) or the Canadian Ice Service (CIS). The Northern Sea Route, north of the European Russian and Siberian coasts, has remained largely clear of ice for the entire month.

Warm surface water near Alaska and the Kara Sea

Figure 6. The map shows average ocean sea surface temperature (SST) and sea ice concentration for August 30, 2015. SST is measured by satellites using thermal emission sensors (a global product, adjusted by comparison with ship and buoy data). Sea ice concentration is derived from NSIDC’s sea ice concentration near-real-time product. Also shown are drifting buoy temperatures at 2.5 meters depth in the ocean (about 8 feet deep: colored circles); gray circles indicates that temperature data from the buoys is not available.

Credit: M. Steele, Polar Science Center/University of Washington
High-resolution image

Strong winds from the east in spring of this year opened the ice pack in the eastern Beaufort Sea quite early, allowing early warming of the ocean surface. However, the winds shifted in later spring, forcing the warmed water layer against the North American mainland rather than dispersing it further into the Arctic Ocean. Sea surface temperatures (SSTs) were high as of late August 2015 in the Beaufort, Chukchi, and Laptev Seas, as well as in Baffin Bay and the Kara and northern Barents seas.

The remaining area of low concentration ice in the Beaufort Sea has large pockets of warming open water. This area is likely to melt out by the September ice minimum; however, maximum SSTs in this region will probably not be especially high (currently about 2.5 degrees Celsius, or 5 degrees Fahrenheit above the freezing point of seawater) owing to how late we are in the melt season.

NASA airborne mission flies over sea ice in 2015 to support ICESat-2

images from air campaign

Figure 7. The map at left shows flight tracks flown by NASA to evaluate laser reflection characteristics over sea ice and land ice. The image at top right shows sea ice with melt ponds in the Lincoln Sea. The photo at bottom right shows the view from the aircraft window of moderately loose pack in the area.

Credit: K. Brunt/NASA
High-resolution image

In support of the upcoming Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) mission, NASA recently deployed two instrumented aircraft to Thule Air Force Base, Greenland (near Qaanaaq) to collect data for the development of software to process the satellite data. Instrumentation for the three-week campaign (July 28 to August 19) included a laser altimeter called SIMPL and an imaging spectrometer called AVIRIS-NG. ICESat-2 is a satellite-borne laser altimetry mission that uses a new approach to space-borne determination of surface elevation, based on a high measurement rate (10,000 times per second), multiple ground tracks of laser data, and closely spaced orbital tracks to provide more detailed mapping. Specific science goals of the airborne campaign include assessing how melting ice surfaces and snow-grain-size variability affect the surface return of green-wavelength light (the color of the ICESat-2 lasers).

Over sea ice, the aircraft data provide important information on sea ice freeboard (height of flotation) and snow cover on sea ice. Both are important parameters for correcting satellite measurements of sea ice thickness. Of the more than thirty-five science flight hours of data collected based out of Thule, four flights targeted sea ice in the vicinity of Nares Strait, where loose pack ice, covered in surface melt ponds, was found. These data will be available on the NASA ICESat-2 Web site later in the year.