Climate Science News
As of August 14, Arctic sea ice extent is tracking third lowest in the satellite record. The southern route through the Northwest Passage appears to be largely free of ice. Despite a rather diffuse ice cover in the Chukchi Sea, it is unlikely that Arctic sea ice extent this September will fall below the record minimum set in 2012.Overview of conditions
As of August 14, Arctic sea ice extent was 5.61 million square kilometers (2.17 million square miles). This is the third lowest extent in the satellite record for this date and slightly below the two standard deviation range. So far this month the rate of loss has been faster than average and has declined at a rate similar to that observed for 2012.
Ice loss has progressed quite rapidly in the Beaufort and Chukchi seas, where broken up ice floes are starting to melt away. However, large, thick multiyear ice floes persist in several areas; it remains to be seen if they will survive the melt season. A wedge of open water has also penetrated northward from the East Siberian Sea, yet ice remains extensive in the Laptev Sea, blocking the Northern Sea Route. Ice extent continues to be low in the Kara, Barents, and East Greenland seas. The southern (Amundsen’s) route through the Northwest Passage appears open in Advanced Scanning Microwave Radiometer 2 (AMSR2) data. However, data in visible wavelengths from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) instrument still show some ice.Conditions in context
Ice loss from August 1 to 14 was faster than average, at 87,400 square kilometers (33,800 square miles) per day, and near the rates observed in 2012. Nevertheless, as has been the pattern this summer, atmospheric conditions through the first half of August have been generally cloudy and cool. Air temperatures at the 925 hPa level were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below the 1981 to 2010 long-term average over the eastern part of the Arctic Ocean and near average elsewhere. The cool and cloudy conditions reflect a pattern of low atmospheric pressure over the Laptev and Kara seas.
As of August 16, a strong storm (central pressure of 968 hPa) was located over the Central Arctic Ocean at about 85 degrees North, near the dateline. The extent to which this strong storm will affect sea ice conditions remains to be seen.Ocean heat continues ice melt
The Arctic atmosphere is cooling now as the sun dips lower in the sky. However, sea ice loss will continue throughout August due primarily to melt from the ocean heat that has accumulated over the summer. Early ice retreat has allowed the ocean to warm, both from absorption of the sun’s energy and from northward-flowing warm water in the Chukchi Sea to the west of Alaska and in the Barents Sea to the north of Norway. Unusually strong ocean warming occurred in northern Baffin Bay (between northern Canada and Greenland), the Beaufort Sea (north of northwestern Canada and Alaska), the East Siberian Sea (north of far eastern Siberia), and the Barents and Kara seas (north of western Eurasia).
What is quite unusual this year is the early ice retreat and resulting ocean warming in the western Beaufort Sea and in the western East Siberian Sea. The extent of warming to the north of these two seas is also unusual, as well as the extent of this warming to the north. These two areas typically melt out later in the season, when atmospheric heating rates have declined from their mid-summer peak. Thus the exposed ocean warms, but not all that much. This pattern was true during the record-setting year of 2012, when by the end of summer, these areas were substantially cooler than surrounding seas that had melted out earlier.
This year, however, the melt out was early and extensive enough that the ocean has already warmed substantially in these two areas. More sea ice retreat is probable in the western Beaufort and East Siberian seas as well as areas in the coming weeks. But what about the ocean’s response? Some warm water might move northward via ocean currents and contribute to ice melt. However, further dramatic ocean surface warming is unlikely, given that the atmosphere is already cooling, especially in far northern latitudes.Ice loss rates indicate little chance for a record low this year
While there are still three to four weeks to go in the melt season, a new record low this September is highly unlikely. A simple projection method developed by Walt Meier at the NASA Goddard Space Flight Center uses daily ice loss rates from previous years to estimate possible trajectories of ice extent through the rest of the melt season.
This approach yields a range of minimum values based on how sea ice loss progressed in previous years. By selecting from an average of multiple years, or using loss rates from a specific previous year, the method yields an estimate of the likely range of the minimum sea ice extent. As of August 14, using daily ice loss rates based on the 2006 to 2015 average yields an average projected 2016 minimum extent of 4.33 million square kilometers (1.67 million square miles). Using the slowest (recent) August to September decline, which occurred in 2006, yields a 2016 minimum of 4.76 million square kilometers (1.84 million square miles). Using the fastest rate of decline, from 2012, yields a 2016 minimum extent of 4.06 million square kilometers (1.57 million square miles). These two years bracket a reasonable range of expected 2016 minima. It is possible that this year will have decline rates that fall outside the range of previous years. However, this approach indicates that it is very unlikely that 2016 will have a minimum below 2012’s value of 3.39 million square kilometers (1.31 million square miles). A projection from August 1 was submitted to the Sea Ice Outlook.Further reading
Lindsay, R.W. 1998. Temporal variability of the energy balance of thick Arctic pack ice, Journal of Climate, doi:10.1175/15200442(1998)011<0313:TVOTEB>2.0.CO;2.
Steele, M. and W. Ermold. 2015. Loitering of the retreating sea ice edge in the Arctic seas, Journal of Geophysical Research, doi:10.1002/2015JC011182.
Steele, M., J. Zhang, and W. Ermold. 2010. Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt, Journal of Geophysical Research, doi:10.1029/2009JC005849.
An extensive area of lower than average temperatures in the Central Arctic and the Siberian coast, attended by persistent low pressure systems in the same region, led to slightly slower than average sea ice decline through the month. The stormy pattern contributed to a dispersed and ragged western Arctic ice pack for July, with several polynyas beginning to form late in the month. A new record low September ice extent now appears to be unlikely.Overview of conditions
Arctic sea ice extent for July averaged 8.13 million square kilometers (3.14 million square miles), the third lowest July extent in the satellite record. This makes July only the second month so far this year that did not have a record low extent. July’s extent is 190,000 square kilometers (73,000 square miles) above the previous record low set in 2011, and 1.65 million square kilometers (637,000 square miles) below the 1981 to 2010 long-term average.
Ice extent continues to be far below average in the Kara and Barents seas, as it has been throughout the winter and spring. Extent also remains well below average in the Beaufort Sea, but in the Laptev and East Siberian seas, sea ice extent is near average.Conditions in context
The rate of ice loss during July 2016 was slightly below average at 83,800 square kilometers (32,400 square miles) per day. The 1981 to 2010 average rate of ice loss for July is 86,800 square kilometers (33,500 square miles) per day.
Warm conditions with temperatures at the 925 hPa level of 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) above average graced the northernmost coasts of Alaska, Canada, and Greenland, but the thick sea ice that is typical of this region is unlikely to melt out. Very warm conditions continued in the Kara and Barents seas, with temperatures as much as 3 to 6 degrees Celsius (5 to 11 degrees Fahrenheit) above average, consistent with the retreat of the ice cover to the northern edge of the Svalbard, Franz Josef, and New Siberian Islands. However, the main feature of the climate conditions for the month was a large area of below-average pressure centered over the Laptev Sea, and associated cooler than average conditions in the same area (1 to 4 degrees Celsius or 2 to 7 degrees Fahrenheit). This continues the pattern seen in June, with conditions unfavorable to pronounced sea ice retreat: cloudy and cool, with winds that tend to disperse the ice and increase its extent, rather than compact it.July 2016 compared to previous years
Through 2016, the rate of decline for the month of July is 72,700 square kilometers 28,070 square miles) per year, or 7.3 percent per decade. July extent remained above 2011 and 2012 levels throughout the month, but it was below the 2007 extent for the first half of the month.A shift in pressure
Beginning in June there was a significant change in the atmospheric circulation over the Arctic. May was characterized by high pressure over the Arctic Ocean which had persisted since the beginning of the year. However, in June the pattern shifted to lower than average pressure. This brought clouds and fairly low temperatures to the region, slowing ice loss. The change in circulation also shifted the pattern of ice motion, slowing the earlier movement of ice away from the coast in the Beaufort Sea (as depicted in our May 3rd post).
This pattern shift is associated with the development of a large and persistent area of moderate high pressure over the northeastern Pacific (south of Alaska) that formed beginning in mid-May. This may be related to an ongoing shift in the Pacific Decadal Oscillation over spring and early summer this year.Sea ice dances to the changing wind
The shift in air pressure pattern also resulted in a change in sea ice drift directions in the Arctic. Early in the year, sea ice drift had a strong clockwise pattern (Figure 5a, top). However, July conditions greatly reduced sea ice drift speed in the Beaufort Sea and produced a counterclockwise drift pattern in the Laptev Sea (Figure 5a, bottom).
Persistent low pressure and repeated cyclonic storms in the Siberian side of the Arctic tended to disperse the pack and move it away from the coast. By late July, several regions of thin pack and small polynyas were beginning to open in these areas (Figure 5b).The ice of our forefathers
Earlier this month, NOAA at NSIDC published a new compilation of Arctic sea ice extent using a variety of historical sources, including whaling ship reports and several historical ice chart series from Alaska, the Russian Arctic, Canada, and Denmark. The compilation provides a synthesized mid-monthly estimate extending back to 1850. The study concludes that the current downward trend in sea ice has no precedent in duration or scale of ice loss since 1850. With the exception of the Bering Sea, none of the areas have seen sea ice extents as low as in the past decade. Historical periods that show a decrease in summertime sea ice extent in the Arctic, such as the late 1930’s and 1940’s, are smaller in magnitude than the current downward-trending period.Further reading
Walsh, J. E., F. Fetterer, J. S. Stewart, and W. L. Chapman. 2016. A database for depicting Arctic sea ice variations back to 1850. Geographical Review. doi: 10.1111/j.1931-0846.2016.12195.x.
Through the first half of July, Arctic sea ice extent continued tracking close to levels in 2012, the summer that ended with the lowest September extent in the satellite record. The stormy weather pattern that characterized June has persisted into July. Nevertheless, sea ice melt began earlier than average over most of the Arctic Ocean.Overview of conditions
As of July 18, Arctic sea ice extent was 7.82 million square kilometers (3.02 million square miles). This is just below the two standard deviation value for the date, and just above the level observed on the same date in 2012, the year that ended up having the lowest September extent in the satellite record. Throughout the month, extent has closely tracked both the two standard deviation and 2012 levels.
Ice extent in the first half of July was well below average in the Kara and Barents seas, as it has been throughout the winter and spring. Extent is also below average in the Beaufort and Chukchi seas, between the East Siberian and Laptev seas by the New Siberian Islands, and along the southeast coast of Greenland. In the last several days, polynyas have formed in the northern Beaufort Sea. Compared to 2012 at this time of year, there is more ice in the southern Beaufort Sea, Baffin Bay, the Laptev Sea, and north of the New Siberian islands in the East Siberian Sea. There is less ice this year in the East Greenland Sea, extending through the Barents and Kara seas, and in the western Beaufort and Chukchi seas.Conditions in context
The average rate of ice loss through July 18 was 89,500 square kilometers (34,600 square miles) per day, which is close to the long-term average (1981 through 2010) rate of 86,800 square kilometers (33,500 square miles) per day. Recall from our last post that the month of June was characterized by a stormy pattern over the central Arctic Ocean, which likely acted to slow the rate of ice loss. This pattern has persisted into July. However, the rate of decline increased in the first two weeks of the month as very warm conditions spread around the Arctic coasts. Ice loss has slowed in the last few days. A number of low pressure systems, primarily generated over northern Eurasia, have migrated into the central Arctic Ocean, north of the East Siberian Sea. One of these was quite strong, with a central pressure dropping to as low as 979 hPa (Figure 3).
Cyclones found over the central Arctic Ocean in summer tend to be what is termed “cold cored.” Because of these cold-cored systems and their associated pattern of winds, air temperatures at the 925 hPa level for the first half of July have been well below average along and north of the East Siberian Sea. By sharp contrast, strongly above average temperatures have been the rule over the Barents and Kara seas, the Canadian Arctic Archipelago and northern Alaska (Figure 4). Local conditions can be quite variable, and not well captured by conditions at the 925 hPa level. On July 14, Deadhorse, on the North Slope of Alaska on the shores of the Beaufort Sea, saw a record high temperature. The reading of 85° Fahrenheit (through 7 p.m.) broke the record of 83° Fahrenheit set in 1991. It is also also the highest reading on record for any Alaska station within 50 miles of the Arctic Ocean coast north of the Brooks Range.Early melt onset
Seasonal onset of surface melt was early over most of the Arctic Ocean (Figure 5). This occurred under the high-pressure-dominated weather pattern that was present earlier in the spring. The onset of surface melt can be determined with the same passive microwave data used to determine sea ice extent and concentration. Melt began in late April/early May in the southern Beaufort Sea, which was about 6 weeks (more than 40 days) earlier than average. Melt also began a month earlier than average in the Barents Sea and northern Baffin Bay.
Early onset of melt is important because melt drops the surface albedo, allowing the sea ice and its overlying snow cover to absorb more solar radiation, which accelerates the melt process. Data from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) satellite instrument show many very large, multiyear ice floes in the Beaufort Sea, one of them about 50 miles across. It will be interesting to see if these large multiyear floes melt out this summer. NSIDC will be closely monitoring the situation.New insights into Antarctic sea ice conditions
Gerald Meehl of the National Center for Atmospheric Research led a new study shedding light on the upward trend in total Antarctic sea ice extent over the period of satellite observations. The overall view from climate models is that Antarctic sea ice extent should have decreased in response to the general warming of climate. This has led some scientists to suggest that the climate models are fundamentally flawed. However, an explanation for the expanding Antarctic sea ice appears to lie in the Interdecadal Pacific Oscillation (IPO), a natural mode of climate variability. The IPO transitioned from a positive to a negative phase in the late 1990s at the same time that the increase in total Antarctic sea ice extent accelerated. The negative IPO brought a cooling of tropical Pacific sea surface temperatures, and deepening of the Amundsen Sea Low near Antarctica. This has contributed to regional circulation changes in the Ross Sea region favoring expansion of the sea ice cover. Meehl’s study also shows that the negative phase of the IPO in coupled global climate models is characterized by patterns similar to the sea-level pressure and 850 hPa wind changes observed in all seasons near Antarctica since 2000, particularly in the Ross Sea region. Additional model experiments show that these atmospheric circulation changes are mainly driven by precipitation and convective heating anomalies related to the IPO in the equatorial eastern Pacific. They conclude that the models are not wrong, but instead can simulate the processes involved with natural climate variability that results in increased Antarctic sea ice, even when global temperatures are rising.Reference
Meehl, G.A., J.M. Arblaster, C. Bitz, C.T.Y. Chung, and H. Teng. 2016. Antarctic sea ice expansion between 2000-2014 driven by tropical Pacific decadal climate variability. Nature Geoscience, doi:10.1038/NGEO2751.
June set another satellite-era record low for average sea ice extent, despite slower than average rates of ice loss. The slow rate of ice loss reflects the prevailing atmospheric pattern, with low pressure centered over the central Arctic Ocean and lower than average temperatures over the Beaufort Sea.Overview of conditions
Arctic sea ice extent during June 2016 averaged 10.60 million square kilometers (4.09 million square miles), the lowest in the satellite record for the month. So far, March is the only month in 2016 that has not set a new record low for Arctic-wide sea ice extent (March 2016 was second lowest, just above 2015). June extent was 260,000 square kilometers (100,000 square miles) below the previous record set in 2010, and 1.36 million square kilometers (525,000 square miles) below the 1981 to 2010 long-term average.
Sea ice extent remains below average in the Kara and Barents seas, as it has throughout the winter and spring. Despite lower than average temperatures over the Beaufort Sea, sea ice extent there remains below average, and was the second lowest extent for the month of June during the satellite data record.Conditions in context
The average rate of ice loss during June 2016 was 56,900 square kilometers (22,000 square miles) per day, but was marked by two distinct regimes. First, there was a period of slow loss during June 4 to 14 of only 37,000 square kilometers (14,000 square miles) per day. This was followed by above average rates (74,000 square kilometers, or 29,000 square miles) for the rest of the month. For the month as a whole, the rate of loss was close to average (53,600 square kilometers per day). The slow ice loss during early June was a result of a significant change in the atmospheric circulation. May was characterized by high surface pressure over the Arctic Ocean, a basic pattern that has held since the beginning of the year. However, June saw a marked shift to low pressure over the central Arctic Ocean. This type of pattern is known to inhibit ice loss. A low pressure pattern is associated with more cloud cover, limiting the input of solar energy to the surface, as well as generally below average air temperatures. However, in June 2016, it was only in the Beaufort Sea where air temperatures at the 925 hPa level were distinctly below average (about 2 degrees Celsius below average, or 4 degrees Fahrenheit). The change in circulation also shifted the pattern of ice motion. In general, winds associated with such a low pressure pattern will tend to spread the ice out (that is, cause the ice to diverge).June 2016 compared to previous years
Through 2016, the rate of decline for the month of June is 44,600 square kilometers (17,200 square miles) per year, or 3.7 percent per decade. June extent remained below 2012 levels throughout the month, but it was above the 2010 extent for several days. 2010 had the lowest extent for several days during June.View from above
The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the NASA Aqua and Terra satellites provide multiple views each day of the Arctic, and in summer the entire region is sunlit. Two mosaics for June 9 and June 28 show the seasonal progression in surface melting and darkening of the sea ice; the blue-green areas where surface ponding is present; and the movement of large sea ice floes in the Beaufort Sea. On June 9, the ponds are most evident in the Laptev Sea off the coast of Siberia; on June 28, the ponds are most evident in the Canadian Archipelago.
A quick look at sea ice thickness fields
Results from NASA’s Operation IceBridge aircraft missions conducted during late April and early May indicate that ice thicknesses from the Alaskan coast of the Beaufort Sea up to the North Pole were generally in the 2 to 3 meter range (7 to 10 feet), indicative of multiyear ice. However, substantial variations were found along the flight transects with several locations showing an ice thickness of 1.5 meters (5 feet) or less, indicative of first-year ice, while in other locations thicknesses were over 5 meters (16 feet), corresponding to either fairly thick multiyear ice or ridged first-year ice. This substantial variation is representative of a broken up and variegated ice pack with thick multiyear floes interspersed with thinner first-year ice.
The first-year thicknesses were found to be generally thinner than is typical at the end of winter, which is consistent with the usually high temperatures characterizing last winter. Very thin ice (less than 0.5 meters, or 1.6 feet) was found in places near the Alaskan coast, where leads opened up fairly late in the ice growth season. The IceBridge results are generally in agreement with the ice thickness surveys conducted in early April by researchers from York University, and with CryoSat-2 thickness maps discussed in our previous post.Sea Ice Outlook
Each summer the Sea Ice Prediction Network (SIPN) requests forecasts of the September average sea ice extent. Requests are made in June July and August. This year, thirty contributions to the June Sea Ice Outlook were received, employing a variety of methods, including statistical models, dynamical models, and informal polls. The median prediction for this year’s September sea ice extent is 4.28 million square kilometers (1.65 million square miles), similar to the extent observed in 2007. Dynamical models predict 4.58 million square kilometers (1.77 million square miles), compared to the slightly lower overall median extent prediction of 4.28 million square kilometers (1.65 million square miles) from statistical models. The lowest median extent comes from the heuristic contributions (4.0 million square kilometers, or 1.5 million square miles). Only one forecast points towards a new record low for 2016.Antarctic sea ice
Antarctic sea ice extent continues to track at near average levels, in sharp contrast to the previous two winters, which were above average. While the total ice extent in the Antarctic shows a small positive trend, particularly during the cold season, whether or not the total mass of the ice has changed depends on how much of the pack ice consists of consolidated ice, the extent of the marginal ice zone (the outer edge of the ice pack, which is lower in ice concentration), and coastal polynyas (open water areas near the coast). The marginal sea ice zone and the coastal polynyas have important biological implications. These are key regions for phytoplankton productivity and krill abundance that in turn feed Antarctic sea birds and nektonic fauna (things that swim).
A new study looks at how these regions are changing using two sea ice concentration algorithms distributed by NSIDC. While the algorithms give similar trends in the overall sea ice extent, they differ in terms of whether or not the sea ice cover is becoming more compacted (i.e., the consolidated ice pack is increasing in extent) or if the marginal ice zone is expanding (Figure 6). When sea ice is is growing seasonally, both algorithms indicate that it is due to an expansion of the consolidated ice pack, whereas during winter and spring, one measurement method (the NASA Team algorithm) finds the marginal ice zone is also expanding as well, and the other measurement (Bootstrap algorithm) shows no significant trend in the marginal ice. The algorithms also differ in how much of the total ice pack consists of pack ice or the marginal ice, with the NASA Team algorithm having on average twice as large of a marginal ice zone as the Bootstrap algorithm. As well, the NASA Team algorithm is known to underestimate ice concentration in the Antarctic. This highlights the need for further validation of sea ice concentrations derived from passive microwave satellite data.New Sea Ice Index version
As part of our quality control process, the Sea Ice Index, which supplies sea ice extent and concentration values, has been updated to Version 2. Changes include using the most recently available version of the Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data that provide final sea ice concentration data. The version update also adjusted three procedures in the Sea Ice Index processing routine that affected both the near-real-time data and the final data. These four updates affect different portions of the Sea Ice Index time series. Because of these updates, minor changes in some of the ice extent and area numbers will be seen. However, these changes are almost all quite small and do not alter current conclusions about Arctic or Antarctic sea ice conditions. More information on Version 2 is available in the Sea Ice Index documentation.Reference
Stroeve, J. C., Jenouvrier, S., Campbell, G. G., Barbraud, C., and Delord, K. 2016, in review. Mapping and assessing variability in the Antarctic Marginal Ice Zone, the pack ice and coastal polynyas. The Cryosphere Discuss., doi:10.5194/tc-2016-26.
As of June 14, 2016, NSIDC has completed the transition to the Defense Meteorological Satellite Program (DMSP) F-18 satellite for sea ice data. Sea Ice Index updates have also resumed.
Sea ice data in Arctic Sea Ice News and Analysis are now based on the F-18 satellite beginning April 1, 2016. Data before April 1 are still from the F-17 satellite or earlier satellites in the series.
For more information on the F-17 satellite issues, see our April 12, 2016 post. On May 6, updates resumed with provisional F-18 data. These data are no longer considered provisional. However, these are near-real-time data and numbers may change when final data are obtained.
For more information on the satellite transition, see the documentation for the Near-Real-Time DMSP SSMIS Daily Polar Gridded Sea Ice Concentrations data set.
Daily Arctic sea ice extents for May 2016 tracked two to four weeks ahead of levels seen in 2012, which had the lowest September extent in the satellite record. Current sea ice extent numbers are tentative due to the preliminary nature of the DMSP F-18 satellite data, but are supported by other data sources. An unusually early retreat of sea ice in the Beaufort Sea and pulses of warm air entering the Arctic from eastern Siberia and northernmost Europe are in part driving below-average ice conditions. Snow cover in the Northern Hemisphere was the lowest in fifty years for April and the fourth lowest for May. Antarctic sea ice extent grew slowly during the austral autumn and was below average for most of May.Overview of conditions
May 2016 set a new record low for the month for the period of satellite observations, at 12.0 million square kilometers (4.63 million square miles), following on previous record lows this year in January, February, and April. May’s average ice extent is 580,000 square kilometers (224,000 square miles) below the previous record low for the month set in 2004, and 1.39 million square kilometers (537,000 square miles) below the 1981 to 2010 long-term average.
During the month, daily sea ice extents tracked about 600,000 square kilometers (232,000 square miles) below any previous year in the 38-year satellite record. Daily extents in May were also two to four weeks ahead of levels seen in 2012, which had the lowest September extent in the satellite record. The monthly average extent for May 2016 is more than one million square kilometers (386,000 square miles) below that observed in May 2012.
Sea ice extent remains below average in the Kara and Barents seas, continuing the pattern seen throughout winter 2015 and 2016. Sea ice also remains below average in the Bering Sea and the East Greenland Sea. In the Beaufort Sea, large open water areas have formed near the coast and ice to the north is strongly fragmented due to wind-driven divergence. The opening began in February, continued through March, and greatly expanded in April.Conditions in context
The average ice loss during May 2016 was 61,000 square kilometers (23,600 square miles) per day. This was faster than the 1981 to 2010 long-term average rate of decline of 46,600 square kilometers (18,000 square miles) per day. May air temperatures at the 925 hPa level were 2 to 3 degrees Celsius (4 to 5 degrees Fahrenheit) above the 1981 to 2010 average across most of the Arctic Ocean, with localized higher temperatures in the Chukchi Sea (4 to 5 degrees Celsius or 7 to 9 degrees Fahrenheit) and in the Barents Sea (4 degrees Celsius or 7 degrees Fahrenheit). Air pressure patterns were not particularly unusual, but two areas of southerly winds in northern Europe and Alaska pushed higher than average temperatures into the Arctic Ocean, producing hot spots noted above and generally above-average temperatures across the Arctic. Only over central Siberia were temperatures lower than the 1981 to 2010 average.May 2016 compared to previous years
Through 2016, the rate of decline for the month of May is 34,000 square kilometers (13,000 square miles) per year, or 2.6 percent per decade.Thickness in the Beaufort Sea
Satellite and survey data show that ice thicknesses in parts of the Arctic are similar to those observed in 2015, but that ice thickness over the whole region is thinner compared to the last five years. Ice thickness surveys carried out by York University in early April 2016 show that thicknesses in the Northwest Passage are similar to that in 2015, though there is less multiyear ice in 2016. In the southern Beaufort Sea, the thickness of multiyear ice is also similar to the previous year, but because of strong divergence and export, first-year sea ice is considerably thinner than in 2015, giving rise to expectations of earlier melt out of this thin ice and formation of open water in 2016. Data from the European Space Agency’s CryoSat-2 satellite show that first-year ice in March 2016 is thinner compared to the March 2011 to 2016 average, especially in the Beaufort Sea (20 to 40 centimeters thinner) and the Barents and Kara seas (10 to 30 centimeters thinner). Multiyear ice north of Canada and Greenland is also thinner.
The thinner first year ice may partly explain the early development of open water in the southern Beaufort Sea for this month. The multiyear ice on the other hand may survive and slow down the overall retreat of the ice edge, as it did in 2015 when a band of multiyear ice survived throughout most of the summer. However, the multiyear ice regime this year seems more fragmented and interspersed with thinner first-year ice. When this thinner ice melts, dark open water areas may grow rapidly as energy is absorbed which in turn melts more ice and can accelerate multiyear ice decay.Fragmented ice in the Beaufort Sea
As discussed in last month’s post, a large area in the Beaufort Sea shows a very fragmented ice cover as a result of strong wind-driven divergence throughout the late winter and spring. Figure 5 shows a MODIS visible-band image from May 21, 2016 for the southern Beaufort Sea, illustrating how the fragmentation has led to large multiyear ice floes surrounded by first-year ice and open water. The area of fragmented ice now nearly reaches the pole. While thick, multiyear ice can better survive the summer melt season, the early development of open water allows temperatures in the ocean mixed layer (top 20 meters) to rise, which may enhance lateral ice melt in that region. In summer 2007, early retreat of sea ice from the coasts of Siberia and Alaska, combined with unusual clear skies, led to enhanced melt of thick multiyear ice floes, some recording nearly 3 meters (10 feet) of bottom melt. If atmospheric conditions this summer are as favorable as they were in 2007, some of this multiyear ice may not survive the summer.Report from the field: Barrow, Alaska
NASA research scientist and NSIDC Arctic Sea Ice Analysis contributor Walt Meier spent the last week in Barrow, Alaska taking part in a National Science Foundation-funded sea ice camp and workshop. The goal was to bring together modelers, remote sensing scientists, and field researchers to understand each other’s work and to develop new ways to collaborate and combine knowledge about the Arctic sea ice system. As part of the camp, groups trudged onto the ice daily to take measurements. They found the ice to be quite thin at 80 to 100 centimeters (31 to 39 inches), compared to an average year when thicknesses would be 140 to 150 centimeters (55 to 59 inches). Melt ponds had already formed, though during cooler days, there was some refreezing as well. The residents of Barrow conveyed that it has been a very unusual winter. Normally, there is quite a bit of onshore wind from the west. This pushes the ice together and grounds pieces to the shallow shelf offshore, which helps stabilize the ice cover. However, this year the winds have been almost always from the east. This keeps the ice near the shore flat and undeformed (which the group observed during the camp) and opens up leads, or areas of open water, at the edge of the fast ice, which is clear in satellite imagery. This westward flow is a part of the larger Beaufort Gyre flow that has dominated the entire Beaufort and Chukchi sea region for much of the winter.Record low snow
The Northern Hemisphere had exceptionally low snow coverage for both April and May of 2016 and a record low spring (March, April, and May), as reported from 50 years of mapping by Rutgers University’s Global Snow Lab. April’s snow cover was the lowest at 27.91 million square kilometers (10.78 million square miles), and May was the fourth lowest at 16.34 million square kilometers (6.3 million square miles).
The National Oceanic and Atmospheric Administration announced on May 20 that Barrow, Alaska recorded the earliest snowmelt (snow-off date) in 78 years of recorded climate history. Typically snow retreats in late June or early July, but this year the snowmelt began on May 13, ten days earlier than the previous record for that location set in 2002.Below average sea ice in the Antarctic
Sea ice extent in the Southern Hemisphere grew fairly slowly in May compared to the average, causing it to dip below the long-term average by the second half of the month. Antarctic sea ice extent for May 2016 averaged 10.70 million square kilometers (4.13 million square miles). This is 90,000 square kilometers (35,000 square miles) below the 1981 to 2010 long-term average of 10.79 million square kilometers (4.17 million square miles). Antarctic sea ice has been trending at near-average to below-average levels since June of 2015. In May 2016, extent was particularly low in the Bellingshausen Sea, Fimbul Ice Shelf area, and Wilkes Land Coast, but well above average in the northwestern Weddell Sea near the Antarctic Peninsula.References
Haas, C. 2012. Airborne observations of the distribution, thickness, and drift of different sea ice types and extreme ice features in the Canadian Beaufort Sea, Proceedings of the Arctic Technology Conference ATC, Houston, Texas, December 3?5, 2012, Paper No. OTC 23812, 8 pp.
Haas, C., and S. E. L. Howell. 2015. Ice thickness in the Northwest Passage, Geophysical Research Letters, 42, doi:10.1002/2015GL065704.
Perovich, D. K., J. A. Richter-Menge, K. F. Jones and B. Light. 2008. Sunlight, water and ice: Extreme Arctic sea ice melt during the summer of 2007, Geophysical Research Letters, 35, L11501, doi:10.1029/2008GL034007.
NSIDC has obtained data from the DMSP F-18 satellite and is in the process of intercalibrating the F-18 data with F-17 data. Intercalibration addresses differences between the series of sensors, in order to provide a long-term, consistent sea ice record. While this work continues, we are displaying the uncalibrated F-18 data in the daily extent image. The daily time series graph shows F-17 data through March 31, and F-18 data from April 1 forward. Initial evaluation of the uncalibrated F-18 data indicates reasonable agreement with F-17, but the data should be considered provisional and quantitative comparisons with other data should not be done at this time.
Because these are provisional data, the Sea Ice Index has not been updated and continues to display only F-17 data through March 31. We expect to make the F-18 data available in Charctic soon.
For general information on the intercalibration of sensors, see the documentation for Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data. This documentation will be updated when the intercalibration to F-18 is complete.
For more information on the F-17 satellite sensor issues, see our previous post.
The Defense Meteorological Satellite Program (DMSP) F17 satellite is experiencing continuing issues with its passive microwave sensor. Data from the 37V channel, used to observe sea ice, have been unusable since early April, although the 37H channel used for the Greenland Ice Sheet Today melt area mapping is unaffected. NSIDC is working to bring the DMSP F18 satellite online for its near-real-time source of data for sea ice monitoring. Based on other data sources, sea ice extent remains far below average for the satellite record period, and likely setting record daily lows. The April sea ice decline rate appears to have been slightly faster than average.Overview of conditions
The Arctic Sea Ice News and Analysis reference sea ice product, the Sea Ice Index, will be suspended until a new calibration can be completed for the F18 satellite, which is underway. The Advanced Microwave Scanning Radiometer 2 (AMSR2) instrument flying on Shizuku (GCOM-W1), a satellite operated by the Japan Aerospace Exploration Agency (JAXA), provides data on sea ice extent and rates of change, but because it uses a different sensor and processing algorithm, the extent numbers cannot be directly compared with those from the SMMR-SSM/I-SSMIS instruments record; the AMSR2 algorithm gives extents that differ by several tens of thousands of square kilometers, or a fraction of a percent to a few percent of total sea ice extent.
A look at the Arctic Data archive system at the National Institute of Polar Research in Japan reveals that sea ice since mid-April has remained at record low daily levels as assessed over their archive of sea ice extent, and is approximately 400,000 square kilometers (154,400 square miles) below the previous daily record extents at this time. This is supported by another analysis of sea ice extent produced by the University of Bremen using the same satellite but a different sensor channel. Both assessments of sea ice extent indicate that the April rate of decline for 2016 is slightly faster than the long-term average of their respective archives. Another sea ice monitoring site, The Cryosphere Today, continues to use the DMSP F17 data, and their graphics show evidence of the sensor issues. This site reports sea ice area in its graphical trend, not extent (area of ocean with at least 15% sea ice coverage) as do the other sites and NSIDC. However, the trend and record low daily extents for the second half of April may be interpreted from these data as well.Conditions in context
April 2016 was quite warm over nearly all of the Arctic Ocean. Air temperatures at the 925 hPa level (about 2,500 feet above the surface) were typically 3 to 5 degrees Celsius (6 to 9 degrees Fahrenheit) above average over the central Arctic Ocean, with larger positive departures compared to average over central Siberia (6 to 8 degrees Celsius, or 11 to 18 degrees Fahrenheit). The sea level pressure pattern featured above average pressures over the Beaufort Sea north of Alaska, and below average pressures over the Aleutians, western Baffin Bay, and Scandinavia. The April 2016 Arctic Oscillation Index transitioned from positive to negative through the month, consistent with the varied patterns of pressure over the Arctic. See our previous discussion of the Arctic Oscillation.
Using a series of images from the Moderate Resolution Imaging Spectrometer (MODIS) from NASA Worldview, we created a short video showing sea ice drift north of Alaska in the Beaufort Sea. The strong anti-cyclonic (high air pressure) pattern produced surface winds that fractured the ice, twisting it in a clockwise direction and opening the pack ice significantly. Dramatic, similar fracturing of sea ice in the Beaufort Sea has been noted in earlier posts (see March 6, 2013).
Motion in the ocean
The NSIDC sea ice motion and sea ice age products have recently been updated via a release of Version 3. This version was created by re-running the previous algorithms, and incorporating a few improvements. First, a number of unrealistic AVHRR and buoy velocities that had been noted were removed. Also, a more accurate sea ice mask, based on the same sea ice concentration product used in our sea ice extent analysis, was implemented. Finally, the Version 3 updates include buoy-derived motions in the Arctic through the entire time series (1979 to 2015). Near-real-time processing of provisional ice age data, which are frequently shown here as a first look at ice conditions, has also been updated to include some of the improvements of Version 3, including the incorporation of near-real-time buoy data and NSIDC’s near-real-time sea ice concentration product as the basis for the sea ice mask. As with any near-real-time product, the fields should be considered provisional and are subject to change. Full details of the product changes and the new processing methods are included in the product documentation for Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors, Version 3 and EASE-Grid Sea Ice Age, Version 3.
Monthly mean of Sea Level Anomalies (annual and seasonal cycles removed)measured by altimetry over the Pacific for August 1997 (left) and August 2015 (right). Credits CNES/CLS.Further information:
- Indicators: ENSO
- Applications: Climate, ENSO
- Image of the month, July 2015 "El Niño's return, west side story".
- ENSO current conditions on CPC/NCEP website
- Météo France (2015/08/28): Vers un épisode El Niño de forte intensité (in french)