Climate Science News
Arctic sea ice extent continued a rapid retreat through the first two weeks of July as a high pressure cell moved over the central Arctic Ocean, bringing higher temperatures. Antarctic sea ice extent increased rapidly through June and early July, and reached new daily record highs through most of this year.Overview of conditions
During the second half of June, the rate of sea ice loss in the Arctic was the second fastest in the satellite data record. As a result, by the beginning of July extent fell very close to two standard deviations below the long-term (1981 to 2010) average.
The rate of ice loss for the first half of July averaged 104,000 square kilometers (40,000 square miles) per day, 21% faster than the long-term average for this period.
Ice loss during the first two weeks of July 2014 was dominated by retreat within the Laptev Sea, and within the Kara and Beaufort seas. Open water areas now exist north of 80 degrees North in the Laptev Sea. Ice cover remains fairly extensive in the Beaufort and Kara seas compared to recent summers.
By July 15, ice extent had fallen to within 440,000 square kilometers (170,000 square miles) of that seen in 2012 (the modern satellite-era record minimum) on the same date, and was 1.54 million square kilometers (595,000 square miles) below the 1981 to 2010 average. However, ice concentration remains high within the central Arctic Ocean, particularly compared to 2012.Conditions in context
The first half of July 2014 was dominated by anomalously high sea level pressure over the Arctic Ocean and the Barents Sea, coupled with below-average sea level pressure over Iceland. Air temperatures at the 925 millibar level (or about 2,500 feet above the surface) were mostly 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) above average over parts of the Arctic Ocean, leading to surface melting. Air temperatures were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below average in the Kara and Barents seas, where melt has generally been off to a slower start than average this summer. Ice extent remains below average in the Laptev and East Greenland seas and Baffin Bay, and is near average to locally below average in the Beaufort, Chukchi and Kara seas.Onset of summer melt
In general there has been a trend over the satellite data record towards earlier melt onset in the Arctic. Melt usually now begins an average of 7 days earlier than in the late 1970s and early 1980s, or at a rate of about 2 days earlier per decade. However, in regions such as the Kara and Barents seas, melt has begun on average 5 to 7 days per decade earlier, totaling 18 to 25 days earlier since 1979, helping to foster earlier development of open water in those regions.
Despite statistically significant trends towards earlier melt onset, there remains a lot of year-to-year variability. For example, in 2013, melt was slow to start, particularly over the Arctic Ocean, the Laptev and East Siberian seas, Hudson Bay, and the Bering Sea. By contrast, melt onset in 2012 was generally earlier than average over most of the Arctic Ocean, including the Beaufort, Chukchi, Laptev, and Kara seas, as well as Hudson Bay and Baffin Bay, and later than normal in the East Siberian Sea, the Greenland and Bering seas. While melt began earlier than average this summer in the Beaufort, Chukchi, Bering, and Laptev seas, it has been somewhat slower to start in the East Siberian Sea and in the Kara Sea, as well as in large parts of the central Arctic Ocean.Conditions in Antarctica
On July 1, Antarctic sea ice extent was at 16.16 million square kilometers (6.24 million square miles), or 1.37 million square kilometers (529,000 square miles) above the 1981 to 2010 average. More notably, sea ice extent on that date was 760,000 square kilometers (293,000 square miles) higher than the 2013 extent for the same day, and thus is on pace to possibly surpass the record high extent over the period of satellite observations that was recorded last September.
For June, sea ice concentration and extent were higher than average for the Amundsen, Southern Indian Ocean, and far southern Atlantic (Weddell and eastward) sectors. (See Antarctic reference map.) The regions on either side of the Antarctic Peninsula were among the few sections with lower-than-average concentration and lower sea ice extent. Cooler-than-average ocean conditions are present near the ice edge along the Wilkes Land, Amundsen Sea, and Weddell Sea ice edge, which will favor continued expansion of sea ice in these areas.
Weather patterns over Antarctica during June were characterized by a strong low-pressure pattern over the Amundsen Sea, and lower-than-average air temperatures (1 to 6 degrees Celsius, or 2 to 11 degrees Fahrenheit below average) in the same region. Cool conditions (2 to 3 degrees Celsius or 4 to 5 degrees Fahrenheit below average) surrounded most of the coastal areas of the Antarctic, with the exception of the Peninsula region where, as has also been seen in the first two weeks of July, northerly winds brought warmer-than-average conditions and reduced sea ice extent.Antarctica’s positive trend in sea ice extent
Antarctic sea ice extent also shows a small, long-term upward trend over the period of satellite observations. Antarctica and the Southern Ocean are geographically very different from the Arctic, and are governed by different atmospheric and ocean circulation patterns. Nevertheless, Antarctica has experienced many of the same general signals of Earth’s changing climate as in the Arctic, including general warming, ice sheet loss and faster-flowing glaciers. This makes the small, long-term upward trend in Antarctic sea ice extent rather puzzling. The record sea ice maxima over the past two years (relative to the modern satellite era) have added to the puzzle.
Two recent studies, focused on the back-to-back satellite-era record maxima of 2012 and 2013 (Turner et al., 2013; Reid et al., 2014 in press), point to unusual short-term wind patterns that both fostered ice growth and spread the ice out. In both years, the record-setting extents are related to the size and strength of the Amundsen Sea low pressure area late in the growth season. The more recent study also notes cool ocean water (1 to 2 degrees Celsius or 2 to 4 degrees Fahrenheit below average) persisting near the sea ice edge in the Amundsen-Bellingshausen region in July and August 2013.
Leading ideas regarding the long-term upward trend as assessed over the thirty-five-year satellite record are: (1) persistent changes in wind patterns, resulting from increased westerly winds, which have changed both how much ice is formed and how it is moved around after formation (Holland and Kwok, 2012); and (2) that meltwater from the underside of deep floating ice shelves surrounding the continent (greater than 350 meters, or 1,150 feet thick) has risen to the surface and contributed to a slight freshening of the surface ocean layer (Bintanja et al., 2012). The extra melting results from the changing wind patterns, which act to draw deep warm ocean water inward to the continent to replace surface water and sea ice that is pushed outward and eastward by the stronger westerlies. By thickening, spreading, and stabilizing the polar surface ocean layer (which is comprised of cool, near-freezing water) the increased melt from the ice sheet edges helps sea ice grow around the Antarctic continent.Early satellite data
Antarctica’s sea ice extent has also been highly variable. For example, austral summer minimum ice extents have varied by as much as 25% over the 1979 to 2014 modern satellite record. The June 1979 extent was the highest for a month by a significant margin. Then in 2002, June sea ice extent was the lowest ever recorded. Nine years later, in June 2011, extent tracked below the 1981 to 2010 average.
This variability is underscored by recent assessments of very early satellite images from the Nimbus program of the late 1960s (Gallaher et al., 2014). Mapping of the September 1964 ice edge (at the austral winter sea ice maximum) indicates that 1964 likely exceeded both the 2012 and 2013 record monthly-average maximums, at 19.7±0.3 million square kilometers (7.60±0.11 million square miles). This was followed in August 1966 by an extent estimated at 15.9±0.3 million kilometers (6.13±0.11 million square miles), considerably smaller than the record low August monthly extent set in 1986. It hence appears that Antarctica’s sea ice variability may be greater than the 35-year modern satellite record would indicate, and that the current growth trend, while important, is not yet reaching unprecedented levels seen within the past century.Further reading
Bintanja, R., G. J. Van Oldenborgh, S. S. Drijfhout, B. Wouters, and C. A. Katsman. 2013. Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion, Nature Geoscience, 6, 376–379, doi:10.1038/ngeo1767.
Gallaher, D., G. G. Campbell, and W. N. Meier. 2014. Anomalous variability in Antarctic sea ice extents during the 1960s with the use of Nimbus data. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 7(3), 881-887, doi:10.1109/JSTARS.2013.2264391.
Holland, P., and R. Kwok. 2012. Wind-driven trends in Antarctic sea-ice drift. Nature Geoscience, 5(12), 872-875, doi:10.1038/ngeo1627.
Reid, P., S. Stammerjohn, R. Massom, T. Scambos, and J. Leiser. 2014 in press. The record 2013 Southern Hemisphere sea-ice extent maximum. Annals of Glaciology, in press, 64(69).
Turner J., J. S. Hosking, T. Phillips, and G. J. Marshall. 2013. Temporal and spatial evolution of the Antarctic sea ice prior to the September 2012 record maximum extent. Geophysical Research Letters, 40, 5894–5898, doi:10.1002/2013GL058371.
Ssalto/Duacs maps of Seal Level Anomalies (in cm) made from 4 altimetry mission (Jason-2, Cryosat-2, Saral and HY-2A), on 2014/07/07 when the typhoon is max. The typhoon path is shown by colored circles (the intensity scale is purple for a tropical depression, blue for cat. 1, green for cat. 2, yellow for cat. 3, orange for cat.4 and red for category 5. The dates near the path indicates the date when the hurricane passed. Credits Cnes/CLS Ssalto/Duacs.
Maps of significant wave height (in m) measured along-track by HY-2A over the ocean. Only the ground tracks between the 2014/07/04 and the 2014/07/09 are represented. Credits Cnes/CLS Ssalto/Duacs.Further information:
- Applications: Hurricanes
- Altimetry applications in videos: Monitoring hurricanes
- Nasa Earth Observatory: Typhoon Neoguri
Arctic sea ice extent continues its seasonal decline. Through most of June the pace of decline was near average, but increased towards the end of the month.Overview of conditions
June 2014 averaged 11.31 million square kilometers (4.37 million square miles). This is 580,000 square kilometers (224,000 square miles) below the 1981 to 2010 average for the month.
Large areas of open water quickly opened up in the Laptev Sea at the beginning of June and continued to expand through the month. The southern part of the Beaufort Sea has also opened and melt ponds are apparent on the open drift first-year ice and extending into the pack ice (see Figure 5 below). Nevertheless, ice extent in this region continued to be above the levels of recent years through much of the month. Extent was lower than average in the Barents Sea, Hudson Bay, and the East Greenland Sea, but higher than in recent years in the Kara Sea.Conditions in context
Ice extent during June declined by an average of 78,900 square kilometers (30,500 square miles) per day, faster than the 1981 to 2010 average June rate of 57,200 square kilometers (22,100 square miles) per day. Last March’s relatively low maximum extent helped set the stage for June’s low extent. June is a month that has seen large variability in the rate of ice loss in recent years. In 2012, a period of rapid acceleration occurred during the first half of the month, kick-starting the decline towards the eventual record low extent that September. So far, 2014 has failed to match the 2012 loss rates. However, ice extent on June 30th came within 300,000 square kilometers (115,800 square miles) of that in 2012. The 2014 rate of ice decline also accelerated toward the end of June as wide areas of low-concentration ice on the peripherial areas of the Arctic Ocean opened up, especially in the Hudson and Baffin bays. This increased rate of loss is typical of late June and early July, and is visible in the 30-year mean trend for Arctic sea ice (see the ChArctic interactive sea ice chart).June 2014 compared to previous years
June 2014 is the 6th lowest Arctic sea ice extent in the satellite record, 490,000 square kilometers (189,000 square miles) above the previous record low in June 2010. The monthly linear rate of decline for June is 3.6% per decade.A cooler June
At the 925 mb level (approximately 3000 feet above sea level) average June temperatures over parts of the Arctic Ocean were from 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) below the 1981 to 2010 average, but with a warming trend over the latter half of the month; the last week of June saw temperatures of 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) above average over the central Arctic Ocean. June 2013 was also slightly cooler than average.This is in stark contrast to the unusually warm summers of many recent years, particularly 2012 and 2007 when air temperatures over the Arctic Ocean were up to 4 to 6 degrees Celsius (7 to 11 degrees Fahrenheit), respectively, above average.
The cool conditions in June 2013 were attributed to a generally cyclonic pattern of atmospheric circulation. However, by late June 2014 the more typical pattern of high pressure over the Beaufort Sea had developed, coupled with low pressure over Alaska and Eurasia.Landsat 8 expands Arctic Sea Ice coverage
Landsat 8, launched in February of 2013, has been regularly acquiring images of the world’s daylit land surface since May of that year. The mission recently increased the pace of image acquisition, covering nearly all available daylit areas each day, and expanded coverage of sea ice areas in the Arctic and coastal areas of Greenland (the latter with ascending node, or evening hour, coverage). Coverage for the Arctic Ocean is focused on the far western and far eastern Arctic, that is, the Beaufort, Chukchi, and East Siberian Sea, although substantial coverage of sea ice is included in the acquisition of all Arctic land areas. Ascending (evening) and decending (morning, the typical acquisition time) coverage of coastal Greenland permits better tracking of glacier flow and in particular sea ice break-up and glacier retreat in the fjord areas.
The images, and the historical (somewhat variable) record of Arctic coverage provide information on ice type, surface melting and melt ponds, ice motion, coastal fast ice break-up, lead fraction and shear zones within the ice.More on seasonal thickness evolution of Arctic sea ice
As noted in last month’s post, satellite and airborne sensors are now able to provide good coverage of the Arctic ice thickness. However, as with any remote sensing estimate, the observations come with uncertainty. Direct measurements, even though they do not provide wide-coverage, are important for validation. They can also provide a useful indication of general ice conditions (thickness, temperature) at the beginning of the ice season. Such direct observations, in concert with available satellite and airborne data, can improve seasonal forecasts of sea ice, such as those provided in the recently released Sea Ice Outlook.
In March, the U.S. Navy’s Office of Naval Research (ONR) Marginal Ice Zone project deployed three clusters of mass balance buoys on the sea ice, complementing ongoing similar deployments by the U.S. Army Cold Regions Research and Engineering Laboratory. These mass balance buoys not only provide a simple thickness measurement, but can also provide a time series of the evolution of the ice, both at the top and bottom surface. The ONR buoys additionally include air temperatures sensors, which are useful for monitoring atmospheric conditions, as well as temperatures through and below the ice.
ONR deployed three clusters of buoys in the Beaufort Sea at three different latitudes. Initial ice thickness at the sites was between 1.5 and 2 meters (5 and 6.5 feet). During April and May, there were brief incursions of above freezing air temperatures leading to some melt, but temperatures mostly remained below freezing until early June. All three clusters show continuous above freezing air temperatures starting by the second week of June. With the higher temperatures, melt has commenced on both the top and bottom surfaces.
The Beaufort Sea has been a region of dramatic summer ice loss in recent years, particularly 2012, with regions dominated by thicker, multi-year ice melting out completely. While vigorous melt has begun, it remains to be seen how the ice cover will evolve over the rest of the melt season.
Arctic sea ice extent declined at a typical rate through May, but extent remained below average for the period of satellite observations. While Antarctic sea ice extent increased at a near average rate, extent was at a record high, and above average in nearly every Antarctic sea ice sector.Overview of conditions
Arctic sea ice extent for May averaged 12.78 million square kilometers (4.93 million square miles). This is 610,000 square kilometers (235,500 square miles) below the 1981 to 2010 average for the month. May 2014 is now the third lowest May extent in the satellite record.
Ice extent was lower than average in the Barents and Bering seas. While not visible in the monthly average extent plot, the evolution of the sea ice through the month of May is characterized by the opening of several polynyas along the coast of Siberia, northern Baffin Bay, and along the coast of Hudson Bay. Nevertheless, satellites detected high sea ice concentrations over the Arctic as a whole. This contrasts with 2006, 2007, and 2012 when broad areas of low-concentration ice were observed.
As the melt season is underway in the Arctic, freeze up is in progress in the Antarctic. Sea ice extent for May averaged 12.03 million square kilometers (4.64 million square miles). This is 1.24 million square kilometers (478,800 square miles) above the 1981 to 2010 average for the month. Antarctic sea ice for May 2014 currently ranks as the highest May extent in the satellite record.Conditions in context
May ice extent for the Arctic declined at a fairly steady rate. Sea ice retreated most rapidly in the northern Bering and southern Chukchi seas, and in the Barents Sea where a small area south of the Franz Josef Land archipelago opened late in the month. Weather was dominated by lower-than-average sea level pressure over the Central Arctic Ocean, and higher-than-average pressure over the southern Bering Sea, Alaska, and Canada. This brought about lower-than-average temperatures in the North Greenland Sea and extended toward the poles, as assessed at the 925 hPa level (roughly 3,000 feet). In contrast, warm conditions prevailed over northern Hudson Bay and southern Alaska (2 to 5 degrees Celsius or 4 to 9 degrees Fahrenheit above the 1981 to 2010 average) and the Kara and Laptev seas (1 to 2 degrees Celsius or 2 to 4 degrees Fahrenheit above the 1981 to 2010 average).May 2014 compared to previous years
Arctic sea ice extent dropped at a rate of –44,300 square kilometers (–17,100 square miles) per day, close to the average rate of –45,700 square kilometers (–17,700 square miles) per day. The monthly trend for May is now –2.3% per decade relative to the 1981 to 2010 average.
In the Antarctic, sea ice extent increased at a rate of 108,500 square kilometers (41,900 square miles) per day, very close to the average rate of 108,400 square kilometers (41,850 square miles) per day. For Antarctica, the linear rate of increase for May ice extent is 2.6% per decade relative to the 1981 to 2010 average.Northern Hemisphere snow cover retreats rapidly
After a greater-than-average snow extent in February, snow extent over the Northern Hemisphere shrank rapidly in March, April and May. The Rutgers University Global Snow Lab measured the lowest April snow extent in Eurasia in the 48-year data record. (Erratum: In an earlier version of this post, we mistakenly said that the record low April snow cover was observed in the Northern Hemisphere. We apologize for the error.) In May, snow rapidly retreated in the central Canadian Provinces in North America, and Central Asia (Kazakhstan and northwestern China), where extensive areas had above-average snow cover in February.
Snow cover in central Europe and the desert southwest of the United States were persistently below average throughout the winter and spring of 2013 to 2014. In the United States, this underscores the severe drought in the far southwest and Sierra Nevada. The rapid late spring loss in the Northern Hemisphere continues a decade-long trend toward very low snow cover early in the Arctic sea ice melt season. This resulted in warmer air over darker snow-free areas, which leads to warm air advection over the sea ice
in regions where the snow cover is anomalously low, and dry conditions in the northern boreal forests. These conditions cause increased wildfire activity and soot deposition on the sea ice and the Greenland Ice Sheet surface. High concentrations of soot on the Greenland snow pack and sea ice can contribute to ice retreat and melt.New Arctic sea ice thickness quick look products from IceBridge, ESA CryoSat-2
The NASA IceBridge mission is an airborne campaign to augment and validate satellite measurements of sea ice and ice sheets. This spring, the NASA IceBridge program set a new record of 46 science flights, covering almost 150,000 kilometers (93,200 miles) of flight tracks from March 12, 2014 to April 3, 2014. This included flights over the western Arctic Ocean and north of Greenland to map sea ice thickness and snow depth. NSIDC has published the 2014 quick look product, in addition to a new ESA CryoSat-2 derived sea ice thickness product. Thickness estimates from both products suggest large areas within the western Beaufort Sea that are 1 to 1.5 meters (3 to 5 feet) thick. The tongue of second-year ice that extends up toward the East Siberian Sea is considerably thicker, at 2 to 3 meters (7 to 10 feet) thick. In the eastern Arctic, the ice is predominantly first-year ice, and between 1 and 1.5 meters (3 to 5 feet) thick. The thickest ice is found north of Greenland and near the pole, ranging from 3.5 to 5 meters (11 to 16 feet) thick. The timely release of thickness data from IceBridge and ESA CryoSat-2 provide a valuable resource for seasonal forecasting because they provide an estimate of the ice thickness distribution in the Arctic at the beginning of the melt season.Forecasting needs for Arctic weather and sea ice
The National Oceanic and Atmospheric Administration (NOAA) and the U.S. Navy share a pressing need for better short-term sea ice and weather forecasts to meet their operational responsibilities. With this as a driver, the NOAA Earth Systems Research Laboratory (ESRL) hosted a workshop on Predicting Arctic Weather and Climate, and Related Impacts: Status and Requirements for Progress. The meeting was held on May 13 to 15 in Boulder, Colorado. Participants from the Office of Naval Research and the oceanographer of the Navy’s office outlined their perspective on needs for operational predictions. National Weather Service participants spoke about operational forecasting, while scientists under NOAA’s research arm along with academic scientists gave talks tailored to answering questions from forecasters. The Navy/NOAA/Coast Guard National Ice Center participated as a prime customer for better forecasting capability out of the research community. Operational needs are greatest for forecasts six to eight weeks out, where better availability of data to initialize coupled atmospheric/ocean models offers promise for improvement. Seasonal forecasts of ice melt can be improved with better ice thickness initialization fields. The predictability of the timing of freeze-up at the end of the season appears to depend upon improved sea surface temperature fields.
Kurtz, N. T., Galin, N., and Studinger, M. 2014. An improved CryoSat-2 sea ice freeboard and thickness retrieval algorithm through the use of waveform fitting, The Cryosphere Discuss., 8, 721-768, doi:10.5194/tcd-8-721-2014.
Since reaching its annual maximum extent on March 21, Arctic sea ice extent has declined somewhat unevenly, but has consistently been well below its average 1981 to 2010 extent. While the rate of Arctic-wide retreat was rapid through the first half of April, it has subsequently slowed down. However, ice breakup was quite early in the Bering Sea, presenting difficulties for gold dredging operations and seal hunters in the region. In the Antarctic, sea ice continued to reach record high extents.Overview of conditions
Arctic sea ice extent for April 2014 averaged 14.14 million square kilometers (5.46 million square miles). This is 610,000 square kilometers (236,000 square miles) below the 1981 to 2010 average extent, and 270,000 square kilometers (104,000 square miles) above the record April monthly low, which occurred in 2007. While the rate of ice loss was rapid through the first half of April, it subsequently slowed down. The rate of ice loss averaged for the month was 30,300 square kilometers per day (11,700 square miles per day), which is slower than the average rate of 38,400 square kilometers per day (14,800 square miles per day) over the period 1981 to 2010. As of May 4, 2014, extent was below average in the Barents Sea, Sea of Okhotsk, and the Bering Sea, and slightly above average in Baffin Bay.Conditions in context
Air temperatures at the 925 hPa level (roughly 3,000 feet above the surface) were from 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) above the 1981 to 2010 average over most of the Arctic Ocean, most notably over the East Siberian Sea and in the Bering Strait region. This contrasts with the region centered over Svalbard, where temperatures were up to about 2 degrees Celsius (4 degrees Fahrenheit) below average. The atmospheric circulation pattern as averaged over the month was somewhat unusual, featuring a large area of low sea level pressure centered over the Laptev and Barents seas. Pressures in this region were up to 16 hPa below the 1981 to 2010 average. The transport of warm air from the south along the eastern side of the low pressure area is consistent with the above average temperatures over the East Siberian Sea. The Arctic Oscillation (AO) was in its positive phase through the first three weeks of April, and then regressed to a modestly negative phase.April 2014 compared to previous years
Average ice extent for April 2014 was the fifth lowest for the month in the satellite record. Through 2014, the linear rate of decline for April ice extent is -2.4% per decade relative to the 1981 to 2010 average.Early breakup in the Bering Sea
The anomalously low sea ice conditions in the Bering Sea are partially a result of low winter ice cover (see our March 3, 2014 post) and an unusually early breakup of sea ice. The Fairbanks Daily News Miner reported that the unusually early breakup of ice in the Bering Sea forced several gold dredging operations to act quickly to get their equipment off the coastal sea ice, which is used as a platform to work shallow seabed gold deposits. Seal hunters were also impacted by the early breakup, in some cases abandoning their snowmobiles on the ice as it became unstable or impassable. The snowmobiles were later recovered by boat. The SEARCH Sea Ice for Walrus Outlook provides weekly updates on sea ice conditions within the Bering Sea region for hunters, local communities and others interested in local ice conditions.Importance of spring melt ponds
In spring, snow covers the sea ice on the Arctic Ocean and the albedo, or surface reflectivity, is high. As air temperatures increase, this snow begins to melt and collect on top of the sea ice. Dark melt ponds form, absorbing more energy from the sun than the adjacent bright snow and ice surfaces. A paper recently published in Nature Climate Change by Schröder et al. suggests that the fraction of melt ponds during May plays an important role in how much ice will be left at the end of the melt season in September. Melt ponds enhance the absorption of the sun’s energy by the sea ice pack, melting more snow and ice and further increasing the melt pond fraction. If melt ponds are widespread across the Arctic Ocean by mid-June and into July, under the 24-hour Arctic summer sunlight, then their effect is increased.
The size and number of melt ponds on sea ice are in part governed by the sea ice topography. First-year sea ice is smoother than multiyear ice, and the melt ponds tend to be shallower and more spread out over the first-year ice. While the melt pond fraction in May makes up about 1% of the total summer melt pond fraction, the shift to a predominantly first-year ice pack has helped to increase the number of melt ponds in spring and provides useful input into predictions for September sea ice extent.Antarctic sea ice at record extent
In the Southern Hemisphere, autumn is well underway, and sea ice extent is growing rapidly. Antarctic sea ice extent for April 2014 reached 9.00 million square kilometers (3.47 million square miles), the largest ice extent on record by a significant margin. This exceeds the past record for the satellite era by about 320,000 square kilometers (124,000 square miles), which was set in April 2008.
Following near-record levels in March, a slightly higher-than-average rate of increase led to a record April ice extent, compared to the satellite record since 1978. During April, ice extent increased by an average of 112,600 square kilometers (43,500 square miles) per day. Ice extent on April 30 was a record for that day; record levels continue to be set in early May.
Sea ice extent anomalies are highest in the eastern Weddell Sea (south of the South Atlantic Ocean near longitudes 45°W to 10°E) and along a long stretch of coastline south of Australia and the southeastern Indian Ocean (spanning 40°E to 170°E longitude). These areas of unusual ice extent are following similar anomalies seen in March. April also saw significant ice growth in the Bellingshausen and Amundsen Seas, one of the few regions with lower-than-average ice extents in March. Antarctic sea ice has now been significantly above the satellite average level for 16 consecutive months.
The increased extent in the Weddell Sea region appears to be associated with a broad area of persistent easterly winds in March and April, and lower-than-average temperatures (1 to 2 degrees Celsius, or 2 to 4 degrees Fahrenheit cooler than the 1981-2010 average). A separate region of cool conditions extends over the southern Indian Ocean coastline, with temperatures as much as 2 to 3 degrees Celsius (4 to 5 degrees Fahrenheit) cooler than average. However, across much of the far Southern Hemisphere, temperatures have been above average: for example, in the southern Antarctic Peninsula, temperatures have been 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) above average; in the southern South Pacific, temperatures have been 1.5 to 2.5 degrees Celsius (3 to 4 degrees Fahrenheit) above average, and up to 4 degrees Celsius (7 degrees Fahrenheit) above average in the area near the South Pole.
Schröder D., D. L. Feltham, D. Flocco, M. Tsamados. 2014. September Arctic sea-ice minimum predicted by spring melt-pond fraction. Nature Clim. Change, DOI: 10.1038/NCLIMATE2203.
Arctic sea ice extent for March 2014 averaged 14.80 million square kilometers (5.70 million square miles). This is 730,000 square kilometers (282,000 square miles) below the 1981 to 2010 average extent, and 330,000 square kilometers (127,000 square miles) above the record March monthly low, which happened in 2006. Extent remains slightly below average in the Barents Sea and the Sea of Okhotsk, but is at near-average levels elsewhere. Extent hovered around two standard deviations below the long-term average through February and early March. The middle of March by contrast saw a period of fairly rapid expansion, temporarily bringing extent to within about one standard deviation of the long-term average.Conditions in context
In the Arctic, the maximum extent for the year is reached on average around March 9. However, the timing varies considerably from year to year. This winter the ice cover continued to expand until March 21, reaching 14.91 million square kilometers (5.76 million square miles), making it both the fifth lowest maximum and the fifth latest timing of the maximum since 1979. The latest timing of the maximum extent was on March 31, 2010 and the lowest maximum extent occurred in 2011 (14.63 million square kilometers or 5.65 million square miles).The late-season surge in extent came as the Arctic Oscillation turned strongly positive the second week of March. This was associated with unusually low sea level pressure in the eastern Arctic and the northern North Atlantic. The pattern of surface winds helped to spread out the ice pack in the Barents Sea where the ice cover had been anomalously low all winter. Northeasterly winds also helped push the ice pack southwards in the Bering Sea, another site of persistently low extent earlier in the 2013 to 2014 Arctic winter. Air temperatures however remained unusually high throughout the Arctic during the second half of March, at 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) above the 1981 to 2010 average. March 2014 compared to previous years
Average ice extent for March 2014 was the fifth lowest for the month in the satellite record. Through 2014, the linear rate of decline for March ice extent is 2.6% per decade relative to the 1981 to 2010 average.An increase in multiyear ice
The extent of multiyear ice within the Arctic Ocean is distinctly greater than it was at the beginning of last winter. During the summer of 2013, a larger fraction of first-year ice survived compared to recent years. This ice has now become second-year ice. Additionally, the predominant recirculation of the multiyear ice pack within the Beaufort Gyre this winter and a reduced transport of multiyear ice through Fram Strait maintained the multiyear ice extent throughout the winter.
In Figure 4, Advanced Scatterometer (ASCAT) imagery reveals the distribution of multiyear ice compared to first year ice for March 28, 2013 (yellow line) and March 2, 2014 (blue line). The ASCAT sensor measures the radar–frequency reflection brightness of the sea ice at a few kilometers resolution. Sea ice radar reflectivity is sensitive to the roughness of the ice and the presence of saltwater droplets within newer ice (and, later in the season, the presence of surface melt). Thus older and more deformed multiyear ice appears white or light grey (more reflection), whereas younger, first-year ice looks dark grey and/or black.Ice age tracking confirms large increase in multiyear ice
Satellite data on ice age reveal that multiyear ice within the Arctic basin increased from 2.25 to 3.17 million square kilometers (869,000 to 1,220,000 square miles) between the end of February in 2013 and 2014. This winter the multiyear ice makes up 43% of the icepack compared to only 30% in 2013. While this is a large increase, and may portend a more extensive September ice cover this year compared to last year, the fraction of the Arctic Ocean consisting of multiyear ice remains less than that at the beginning of the 2007 melt season (46%) when a large amount of the multiyear ice melted. The percentage of the Arctic Ocean consisting of ice at least five years or older remains at only 7%, half of what it was in February 2007. Moreover, a large area of the multiyear ice has drifted to the southern Beaufort Sea and East Siberian Sea (north of Alaska and the Lena River delta), where warm conditions are likely to exist later in the year.Summer ice extent remains hard to predict
There is a growing need for reliable sea ice predictions. An effort to gather and summarize seasonal sea ice predictions made by researchers and prediction centers began in 2008. The project, known as the SEARCH Sea Ice Outlook, has collected more than 300 predictions of summer month ice extent. A new study published in Geophysical Research Letters by researchers at NSIDC, University of New Hampshire, and University of Washington reveal a large range in predictive skill. The study found that forecasts are quite accurate when sea ice conditions are close to the downward trend that has been observed in Arctic sea ice for the last 30 years. However, forecasts are not so accurate when sea ice conditions are unusually higher or lower compared to this trend. Results from the study also suggest that while ice conditions during the previous winter are an important predictor (such as the fraction of first-year versus multiyear ice), summer weather patterns also have a large impact on the amount of ice that will be left at the end of summer.Satellite Observations of Arctic Change NSIDC now offers a new Web site, Satellite Observations of Arctic Change (SOAC) with interactive maps of the Arctic based on NASA satellite and related data. The site allows you to explore how conditions in the Arctic have changed over time. Data sets include air temperature, water vapor, sea ice, snow cover, NDVI, soil freezing, and exposed snow and ice. Time periods vary by data set, but range from 1979 to 2013. You can animate a time series, zoom in or out, and view a bar graph of anomalies over time. Links to the source data and documentation are also included. Additional pages provide brief scientific discussion, and overviews of the scientific importance of these data. SOAC was developed with support from NASA Earth Sciences. Reference
Stroeve, J., L. Hamilton, C. M. Bitz, and E. Blanchard-Wrigglesworth. 2014. Predicting September Sea Ice: Ensemble Skill of the SEARCH Sea Ice Outlook 2008–2013. Geophysical Research Letters, Accepted, doi: 10.1002/2014GL059388.Correction
In the caption for Figure 5, we described the map as showing the ages of ice in the Arctic at the end of March. A reader pointed out that this image was for the beginning of March, which is correct. We regret the error and corrected the caption on April 2, 2014 at 1:25 p.m.