2014 melt season in review

Melt extent in Greenland was well above average in 2014, tying for the 7th highest extent in the 35-year satellite record. Overall, climate patterns favored intense west coast and northwest ice sheet melting, with relatively cool conditions in the southeast.

Overview of conditions

melt extent maps

Figure 1. These maps show melt extent patterns for 2011, 2012, 2013, and 2014 for the Greenland Ice Sheet, relative to the average pattern for 1981 to 2010. Red areas indicate a greater number of melt days than average. Data are from the MEaSUREs Greenland Surface Melt Daily 25km EASE-Grid 2.0 data set. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

Melt extent for the Greenland Ice Sheet in 2014 was similar in its regional pattern and intensity to the year 2011, with above average melting in northwestern and western Greenland, and average to below-average southeastern melt. This regional pattern of melting was more or less consistent for June, July, and August. The year 2014 stood in strong contrast to 2012, a record melt year for all areas, and to 2013, when much cooler conditions prevailed in the north. However, unlike the other three years, surface melting in 2014 was generally confined to low elevation areas near the coast.

Conditions in context

temperature and pressure anomaly plots

Figure 2. These plots show Greenland air pressures (left, geopotential height in meters) and air temperatures (right, degrees Celsius) relative to the 1981 to 2010 averages for June, July, and August 2014 combined. Data are at the 700 millibar level, or approximately 10,000 feet above sea level.

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

Weather conditions were dominated by high pressure across the entire island but particularly in the southwest. Previously we noted the association between widespread surface melt and periods of high pressure (see our August post). Unsurprisingly, warm conditions prevailed near the areas of highest melting in the southwest. A few sites in southwestern Greenland (e.g. Kangerlussuaq) experienced the warmest summer on record in 2014, surpassing 2012 (see the NOAA Arctic Report Card for 2014). While average temperatures were 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) warmer than the 1981 to 2010 average over the southwestern coast, conditions were near average over much of the northwest and northern ice sheet. Yet these areas also experienced above average melt extents, consistent with greater absorption of sunlight since 2009 due to darker snow affecting the frequency of surface melting for Greenland.

Greenland in 2014 compared to previous years

graph of melt extent and graph of melt area anomaly

Figure 2. The top graph shows the daily extent of melt during 2014 on the Greenland Ice Sheet surface as a percentage. The 1981 to 2010 average is shown by a blue dashed line. The gray area around this average line shows the two standard deviation range of the data. The bottom graph compares melt area for June to August each year, to the average for 1981 to 2010 for these same months. Data are from the MEaSUREs Greenland Surface Melt Daily 25km EASE-Grid 2.0 data set. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

Comparing the seasonal progression of the four most recent years, the recent tendency for greater-than-average melt extent is apparent, as are the rapid variations in melt extent mid-year. The melt season of 2014 had a series of moderately extensive melt events early on, but did not undergo the expansive areas of surface melt on the high parts of the ice sheet as in 2012.

Relative to the 35 years of continuous satellite measurements, 2014 is tied with 2006 for seventh highest, and is well above the 1981 to 2010 average. Melt area total (the sum of daily melt extents for the entire June through August period) was approximately 100,000 square kilometers (38,600 square miles) above the 1981 to 2010 average. The top eight melt extent years have all occurred since 2002.

NAO you tell me

graph of NAO

Figure 4. This graph plots the North Atlantic Oscillation (NAO) index (blue line) for June, July, and August from 1950 to 2014. The red line shows the NAO trend. Data are from the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center.

Credit: Xavier Fettweis, University of Liège/NOAA
High-resolution image

Recent trends towards increased surface melting in Greenland coincide with a trend in the summertime North Atlantic Oscillation (NAO) pattern, a large-scale climate feature with wide influence over conditions in Greenland. The NAO index is a measure of the strength of the pattern, arbitrarily deemed positive when the main feature of the pattern, low pressure over Greenland and the central Arctic, is stronger than average, and negative when high pressure patterns prevail. Negative values of the NAO climate index are associated with anticyclonic circulation (high pressure, clockwise in the northern hemisphere) over Greenland, producing a tendency to draw warm air from the south along the west coast of Greenland and generally into the North Atlantic. While the NAO has been thought to be a more important feature during the cold season, recent studies find it to be an important metric at other times of the year, through its circulation control on mid-year heat and clear sky delivery to Greenland.

Although summer 2014 had a moderately negative index NAO value, a period of neutral conditions occurred mid-summer at the time of the maximum melt. In contrast, during the summer of 2012 the NAO was intensely negative throughout the whole summer season. This explains why summer 2014 melt was not exceptional, while its average June through August NAO index was negative. However, in mid-June and mid-August, when the NAO was the lowest, some strong anticyclonic conditions resulted in very warm events for the season, consistent with the persistent warm conditions and extensive melting induced by negative NAO conditions.

A darker mood

GrnToday_20Jan2015_Fig5alb

Figure 5a. The Greenland map shows reflectivity (albedo) anomaly, expressed as the percent difference from the average surface reflectance for the summer of 2014 (June, July, and August). Data are from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra and Aqua satellites.

Figure 5b. The plot shows the trend in summer (June, July, August) Greenland ice sheet reflectivity for 2000 to 2014.

Credit: Jason Box, GEUS
High-resolution image

Greenland’s snow and ice was significantly darker in the summer of 2014 than in 2013, and similar to 2011. This darkening trend is apparent in the comparison of the past 15 years of average summer (June through August) reflectivity, shown in Figure 5b. The darker snow absorbs more sunlight, leading to earlier melt onset and overall more melting, even if air temperature conditions are similar to previous years (as was the case in northwestern Greenland in 2014). Darker snow is a result of increased soot, dust, and even microbes in the snow, and the general trend of warmer summer conditions. Snow also darkens over time as jagged snowflakes evolve into rounder snow crystals. The larger snow grain size allows more light to be absorbed by the snow.

Mapping melt from space

Figure 6a. This plot shows total meltwater lake volume in a set of Landsat 8 scenes over Greenland from the summer of 2014. Inset, location of the four satellite image scenes. The orange dot just above the scene outline is the location of Kangerlussuaq, where summer conditions reached record warmth.||Credit: A. Pope et al./Landsat 8|High-resolution image

Figure 6a. This plot shows total surface meltwater lake volume in a set of Landsat 8 scenes over Greenland from the summer of 2014. Inset, location of the four satellite image scenes. The orange dot just above the scene outline is the location of Kangerlussuaq, where summer conditions reached record warmth.

Credit: A. Pope et al./Landsat 8
High-resolution image

GrnToday_20Jan2015_Fig6b_lakes

Figure 6b. Click the image to view the time series of Landsat 8 images of melt ponds on the Greenland Ice Sheet. This set of images was used to make the graph in figure 6a.

Credit: A. Pope et al./Landsat 8
View animated images

Landsat 8, launched in February of 2013, is proving to be a very useful tool for tracking changes in the ice sheets. A pair of ongoing studies at University of Colorado Boulder seeks to determine the best methods for mapping melt lake extent and depth, and both are making extensive use of Landsat 8. Melt lake volume is determined by both absorption of light in the lake water in a single color of the satellite images, or by assessing the ratio of two color channels of the image. Total meltwater volume pattern through the summer changes with latitude, elevation, and summer weather conditions.

Further reading

Arctic Report Card: Update for 2014. http://www.arctic.noaa.gov/reportcard

Box, J. E., X. Fettweis, J. C. Stroeve, M. Tedesco, D. K. Hall, and K. Steffen. 2012. Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers. The Cryosphere 6, 821-839, doi:10.5194/tc-6-821-2012.

Dumont, M., E. Brun, G. Picard, M. Michou, Q. Libois, J. R. Petit, M. Geyer, S. Morin, and B. Josse. 2014. Contribution of light-absorbing impurities in snow to Greenland’s darkening since 200. Nature Geoscience 7, 509-512, doi:10.1038/ngeo2180.

Moussavi, M., W. Abdalati, A. Pope, and T. Scambos. 2015 in prep. Spaceborne derivation and validation of supraglacial lake volume along the western margin of the Greenland Ice Sheet. Remote Sensing of Environment, in preparation.

Pope, A., T. Scambos, M. Moussavi, M. Tedesco, M. Willis, and D. Shean. 2015 in prep. Estimating supraglacial lake depth using Landsat 8. The Cryosphere, in preparation.

Melt calibration, suspension of daily images

The Greenland melt detection algorithm is currently undergoing its annual calibration period. As a result, the daily melt extent mapping image is temporarily suspended. Calibration of the melt detection for each year requires analysis of the springtime snow conditions by a separate program. See our March 13, 2013 post for more discussion of melt calibration.

We will resume the daily image updates in April. A consistent record will be produced later that spans these winter periods retrospectively.

Coming soon: Analysis of the 2014 melt season.

Greenland’s summer: The pressure is on, and off

Melting on the surface of the Greenland Ice Sheet in June and July 2014 has been well above the 1981 to 2010 average in most areas, but after a fast start in May, the southern region and the southeastern coast have seen lower-than-average melt. Mid-summer surface melting did not reach higher elevations (above 2000 meters) as often as in the reference period 1981 to 2010. Short bursts of extensive melting were related to periods of high air pressure over the ice sheet favoring sunny conditions, and promoting increased melting in darker areas of the ice sheet (wet snow, bare ice, or dirty snow).

Overview of conditions

Cumulative melt days and melt anomalies June July 2014

Figure 1. Cumulative days of surface melting (top pair) and anomalies in the number of melt days (bottom pair) for June and July, 2014 (left side and right side, respectively). Anomalies are compared to the period 1981 to 2010. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

Daily melt extent in June surged to nearly 40% of the ice surface area by mid-month and remained above the average extent for the 30-year reference period (1981 to 2010) for almost the entire month. Positive melt day anomalies were present in all areas except for the southeastern ice sheet. In July, melting was intense along the northwestern coast (more than 15 days above the average in some areas) and unusually low along the southeastern coast, especially near Helheim Glacier where July melt days were 3 to 8 days less than average. Overall, melting was less frequent than average in the high interior and southeastern areas of the ice sheet.

 

 

Conditions in context

surface melt and temperature graphs

Figure 2. Melt extent time-series for 2014 (top) and average air temperature anomaly at a level about 800 meters (2,500 feet, 925 hPa) above the sea level for June 1 to August 14, 2014. Melt extent data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. Air temperature data are from the National Center for Environmental Prediction (NCEP) Reanalysis.

Top image credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
Bottom image credit: NOAA Earth System Research Laboratory, Physical Sciences Division
High-resolution image

Thus far, the maximum daily melt extent for summer 2014 was near 40% of the ice sheet surface on June 13. This was the first in a series of four warm periods followed by four periods of near-average conditions spanning the rest of June and July. Since August began, daily melt extent declined to near-average values for late summer. Summer air temperatures for June, July, and the first half of August mirrored the overall pattern of melt intensity, with cooler-than-average conditions about 1degree Celsius (1.8 degrees Fahrenheit) below normal in the high ice sheet plateau, and warmer-than-average conditions along the western coast, especially the southwestern coastal area at 1.5 degrees Celsius (2.7 degrees Fahrenheit) above average.

Models of the Greenland 2014 summer season produced by the MAR version 3.4 model of Xavier Fettweis from Liège University show that the overall snowfall-melt balance for Greenland  (the surface mass balance, or SMB) is very close to the 1981 to 2010 average. While 2013 total autumn snowfall was slightly higher than average, melting in the 2014 summer has now reduced the initial winter 2013 to 2014 snow accumulation surplus. However, despite the high total snow amount, northwestern Greenland had lower-than-normal winter snowfall accumulation. With the onset of a vigorous melt season in that area, the bright white snow cover was quickly removed, exposing darker ice below, and increasing the amount of melting as well as decreasing the ice sheet meltwater retention capacity in this area. This has produced a strong and statistically significant negative mass balance for this summer along Greenland’s northwestern coast.

Melting under pressure

graphs

Figure 3. Three six-day periods in the Greenland surface melt extent daily time-series plot outline periods of high and low melting during June and July. Below, surface air pressure anomaly plots for the same periods (A, B, and C) are shown. A and C are high-melt-extent periods, and show greater-than-average air pressure (2 to 6 millibars); the opposite is true for the low-melt period, B. The two other high-melt periods, June 15 to 20 and July 19 to 25, also show higher-than-average air pressure. Melt extent data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. Air pressure data are from the National Center for Environmental Prediction (NCEP) Reanalysis.

Image credit: National Snow and Ice Data Center
High-resolution image

The four higher-melting periods of mid-June to late July and the intervening periods of more average melt extent appear to be associated with periods of high and low air pressure, respectively. Examining six-day intervals in air pressure reveals higher-than-average pressure dominates during the peaks in surface melt extent, and low pressure during the low-melt periods. High pressure is associated with clear skies, and therefore greater solar energy input to the surface snow, impacting mainly the low albedo zones (in particular the ablation zone). This explains why the melt extent has been abnormally high in the ablation zone and abnormally low in the higher-elevation snow accumulation zone. The melt rate in the accumulation zone is more sensitive to warm but cloudy days and the associated increase in long-wave radiation, due the high surface albedo in this zone. Moderate Resolution Imaging Spectroradiometer (MODIS) images of Greenland on June 13 and July 3 indeed show a mostly cloudless Greenland, whereas more cloud cover is present on June 30 and July 1 during the lower-melt-extent periods.

Sky selfie

ice camp photos

Figure 4. Images of the Greenland Ice Sheet near Kangerlugssuaq in west-central Greenland taken by a drone (UAV) used to evaluate the evolving albedo of the ice sheet surface during the summer melt season. At top left, Prof. Jason Box and Johnny Ryan, a Ph.D. student at Aberystwyth University, hold the drone they used. Top left, the drone takes a picture of the surface (and the operator, J. Ryan) on August 9, 2014 from low altitude, showing numerous cryoconite holes filled with black dust, grit, and soot that had accumulated in the winter snowpack, and melted out of the older ice below. Bottom, a higher-altitude image of the same area reveals sinuous melt streams and linear fractures, as well as small speckles of cryoconite holes on the ice sheet. Tents from the camp are also visible as colorful dots against the ice surface.

Credit: Photos courtesy of Johnny Ryan, Aberystwyth University, Jason Box, GEUS, and Dark Snow Project.
High-resolution image

Our colleague Jason Box of the Geological Survey of Denmark and Greenland (GEUS), and graduate student Johnny Ryan of Aberystwyth University spent much of the summer on the western ice sheet at Camp Dark Snow, near Kangerlugssuaq on the Arctic Circle (67 degrees north latitude at 1,010 meters above sea level). The team was investigating the Greenland surface albedo, climate, and surface melting, and how these evolve during summer. As part of the research, they have been using drones (Unmanned Aerial Vehicles, or UAVs) to photograph the surface from low altitude to examine the development of surface structures associated with melting. Strips of images and albedo measurements from the UAV are compared with simultaneous satellite images from the NASA MODIS sensor as an intermediate state to relate ground albedo measurements with that of the entire ice sheet. UAV photos reveal a surface riven with fractures, and drained by ephemeral rivers of melt water. The mid-summer melt surface in this area is pocked with 0.5 to 1 meter-wide (1.5 to 3 feet-wide) potholes with black grit and dust collected at the bottom. This black material is called cryoconite, and is comprised of dust and soot deposited on the surface, and melted out from the older ice exposed by melting. The dark patches are often glued together by tiny microbes.

Further reading

Fettweis, X., et al. 2014 Greenland ice sheet SMB simulated by MARv3.4 in real time.

Ryan, J.C., A.L. Hubbard, J. Todd, J.R. Carr, J.E. Box, P. Christoffersen, T.O. Holt, and N. Snooke, 2014, in review. Repeat UAV photogrammetry to assess calving front dynamics at a large outlet glacier draining the Greenland Ice Sheet. The Cryosphere Discussions 8, 2243-2275, doi:10.5194/tcd-8-2243-2014.

A warm southern welcome to spring

Surface melting on the Greenland Ice Sheet in May 2014 proceeded quickly, despite cool conditions over wide areas. We continue to explore recent evidence of lower snow reflectivity, and note its likely impact on snow melt during Greenland’s summer season.

Overview of conditions

Map of melt days

Figure 1. These images show the cumulative days of surface melting (left) and anomalies in the number of melt days (right) for May 2014 (31 days). Anomalies are compared to the period 1981 to 2010. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

The 2014 melt season began with a moderately fast start in the southernmost part of the Greenland Ice Sheet in May, on smaller, separate ice caps, and on snow-covered land in the far northeastern part of the island. The early pace of melting was below average for the western coast and most of the southeastern coast, but 4 to 8 days ahead of the normal pace in the far southern ice cap area near the capital of Nuuk.

Conditions in context

plot of surface melt extent

Figure 2a. The graph above shows the daily extent of melt during May 2014 on the Greenland Ice Sheet surface as a percentage. The 1981 to 2010 average is shown by a blue dashed line. The gray area around this average line shows the two standard deviation range of the data. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

Graph of temperature anomalies

Figure 2b. Mean air temperature for May at the 700 millibar level (about 10,000 feet or 3,200 meters altitude). Temperatures for the month were cool over the majority of Greenland.

Credit: National Snow and Ice Data Center, courtesy NOAA/ESRL Physical Sciences Division
High-resolution image

Melting extended over about 10% of Greenland during a brief mid-May warm period in the far south, and then climbed again as the month came to a close. As of this writing in mid-June 2014, melting has rapidly expanded to 30% of Greenland’s ice sheet, and at present favors the western and northern Greenland coast after little activity there in May. Greenland’s weather in May was characterized by cool conditions over the northern two-thirds of the island, but in the south, temperatures were approximately 1 degree Celsius warmer than average for the month, relative to the 1981 to 2010 reference period.

Higher temperatures and a period of light easterly and northeasterly winds in mid-May favored a rapid start to the melt season in southern Greenland. The pattern of melting on the ice sheet, and the timing of melt events, agrees well with the MAR model produced by X. Fettweis at Université de Liège.

 

 

Darkening snow

graph of albedo

Figure 3. This graph shows the mean albedo (reflectivity fraction) of the Greenland Ice Sheet for areas of the ice sheet with an elevation greater than 2,000 meters above sea level. The blue line and blue diamonds show albedo from satellite data. The black line and dots show albedo from a snow model with clean snow, and its evolution under observed summer May and June temperatures. Also shown is the difference between these estimates (red line and diamonds). Modified from Dumont et al., 2014.

Credit: M. Dumont/Météo-France–CNRS, courtesy Nature Geoscience
High-resolution image

A recent research paper by scientists at Météo-France and other French climate science institutions (Dumont et al., 2014) shows that a significant and abrupt shift in albedo took place in 2009. They hypothesize that the increase is due to a persistent increase in the amount of soot or dust in new-fallen snow over the island. This is based on satellite observations of the albedo by the Moderate-resolution Imaging Spectroradiometer (MODIS). When compared to models of the expected reflectivity of clean snow under the summer conditions, the recent satellite observations show that snow over Greenland is darker than can be explained by warm temperatures and coarser snow grains.

Samples of snow from Greenland in recent years favor the idea that dust is the main cause of the darkening. Other studies confirm that the darkening at high elevation (where the impact of a change in dry new-fallen snow would be significant) is about 2%. For clean new snow, a 2% decrease in reflectivity (for example, from 90% to 88%) represents a 15 to 20 percent increase in energy absorption (from 10% to 12%). With a somewhat darker, less pure incoming snowfall, the amount of energy from the sun that the snow absorbs increases, leading to earlier melt, more pronounced melt run-off, and later re-freezing of the ice sheet surface.

Lengthening melt

plot of melt extent

Figure 4. These graphics show trends in how the start (top image) and end (bottom image) of melt season are changing for Greenland. Trends are given in days change per decade. Positive values (red colors) mean that the event is happening later in the year; negative values (blue colors) mean that the event is happening earlier in the year. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

The trend identified by our colleagues in Figure 3 is underscored when we look at the trend in the date of the beginning of melt (melt onset, top image in Figure 4) and the date that the snow and ice finally re-freeze at the end of the season (freeze-up, lower image in Figure 4). Melt day data from 1978 to 2013 show a pronounced trend toward a longer melt season. Melt onset has started 4 to 12 days earlier per decade over this 35 year period (shown by the blue colors). A few areas at high elevation have shown later onset, perhaps due to increasing accumulation of snow at high elevation in Greenland. The end of the melt season, or freeze-up date, has pushed later into the autumn by 8 to 16 days per decade, particularly along the southwestern coast and east-central areas.

Further reading

Dumont, M., E. Brun, G. Picard, M. Michou, Q. Libois, J.-R. Petit, M. Geyer, S. Morin, and B. Josse. 2014. Contribution of light-absorbing impurities in snow to Greenland’s darkening since 2009. Nature Geoscience, doi:10.1038/NGEO2180.

Mote, T., and M. Anderson. 1995. Variations in snowpack melt on the Greenland ice sheet based on passive-microwave measurements. Journal of Glaciology, vol 41, pp 51-60.

2013 in review; 2014 melt begins

The Greenland Ice Sheet had a far more typical melt extent and intensity in 2013 than in 2012, when summer surface melting set a record, compared to satellite observations since 1978. After the normal winter hiatus, the 2014 melting season has now begun again along the southern Greenland coastal areas. We will review the early progress of the 2014 season in our next post, in mid-June.

Overview of conditions

Greenland melt anomaly images

Figure 1. These maps show melt anomalies, or how the number of melt days in each year compared to the average number of melt days as recorded by satellite observations from 1981 to 2010. While 2012 set records for melt extent (center), and 2011 showed strong melt anomalies along the coasts (left), 2013 melt days were within a more typical range, on average (right). Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

Figure 1 shows the cumulative number of days that the Greenland Ice Sheet experienced surface melting during 2013 (right image), along with comparison images for 2011 and for 2012, the record year for melt days.

Overall, 2013 melt intensity, expressed as the number of melt days relative to the 1981 to 2010 average, was slightly to moderately higher than average in the southern and western Greenland Ice Sheet but unusually low along the northern and northeastern coastal areas.

In particular, surface melt did not extend to the higher-elevation interior regions in the north as much as has been typical for the 1981 to 2010 period. A narrow band along the eastern coastline showed significantly greater than average melting, but here as well the surface melt conditions did not extend inland and uphill as they have in recent years.

Conditions in context

Figure 2. The graph above shows the daily extent of melt during 2012 on the Greenland Ice Sheet surface as a percentage, compared to the average from 1981 to 2010. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data||Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia|High-resolution image

Figure 2. The graph above shows the daily extent of melt during 2013 on the Greenland Ice Sheet surface as a percentage. The 1981 to 2010 average is shown by a blue dashed line. The gray area around this average line shows the two standard deviation range of the data. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

In contrast to 2012, the extent of melt was also closer to average during 2013, compared to the period 1981 to 2010.

Extensive melting began slightly later than usual, toward the end of May, but increased rapidly to above-average levels by mid June. A brief reduction in late June and early July was followed by a late-season re-advance in melt area in late July.

 

2013 compared to previous years

Figure 3. Melt extent departure from the average for 1978 to 2013. The area represented by the bars is the sum of the daily melt extent for June, July, and August of each year, with the average subtracted. This highlights the trend in melt, and the scale of past anomalous years. ||Credit: National Snow and Ice Data Center/T. Mote, University of Georgia|  High-resolution image

Figure 3. Melt extent departure from the average for 1978 to 2013. The area represented by the bars is the sum of the daily melt extent for June, July, and August of each year, with the average subtracted. This highlights the trend in melt, and the scale of past anomalous years.

Credit: National Snow and Ice Data Center/T. Mote, University of Georgia
High-resolution image

The 2013 summer in Greenland also saw a reversal of the recent trend in summertime loss of surface snow and ice mass by run-off, as would be expected given the reduced melting. Figure 3 illustrates the relative melt area departure from the average (sum of the daily melt areas over the ice sheet for June, July, and August in each year, with the average area for 1978 to 2013 subtracted). The very large increase in 2012 is clearly shown, as is the return during 2013 to conditions typical of the late 1990s.

Climate conditions during 2013

Graph of NAO

Figure 4. This graph shows the North Atlantic Oscillation Index (NAO) for June through August, for the period 1950 to 2013 (blue dashed line) and running 5-year average (red line). 2013 saw a marked difference from recent years, with average conditions similar to the 1990s and earlier.

Credit: Xavier Fettweis, University of Liège
High-resolution image

Figure 5.

Figure 5. This plot shows air pressure anomalies (left) and air temperature anomalies (right) at the 700 mb level for June to August 2013.

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

Figure 7.

Figure 6. This graph shows anomalies for June through August for total meltwater runoff (blue), snowfall accumulation (red), and net surface mass balance (SMB, green) over the Greenland Ice Sheet from 1960 to 2013, compared to the period 1980 to 1999. The data are from the Modèle Atmosphérique Régional (MAR model), v3.3, and are in gigatons per year. MAR was run at a resolution of 15 kilometers and forced at its lateral boundaries by the ERA-40 reanalysis over 1958-1978 and ERA-Interim afterward.

Credit: Xavier Fettweis, University of Liège
High-resolution image

Weather patterns were significantly different over Greenland during 2013 compared to 2012,  when high temperatures led to extensive melt. A dominant Arctic climate pattern, the North Atlantic Oscillation (Figure 4), was in its positive phase for the summer months (June through August) of 2013, sharply contrasting with a trend that had held for the previous six summers. As discussed in NSIDC Arctic Sea Ice News and Analysis on September 17, 2013, the positive phase of the NAO favors anticyclonic circulation over Greenland. The NAO generally produces warm and dry conditions over Europe and is associated with cooler and higher-precipitation conditions in Greenland and the central Arctic.

Consistent with this, lower-than-average air pressures (Figure 5, left) were observed over Greenland during the 2013 summer, as well as lower temperatures (Figure 5, right). Air temperatures over Greenland were 0.5 to 2 degrees Celsius (1 to 3.6 degrees Fahrenheit) below the 1981 to 2010 averages. Precipitation was also higher in summer 2013.

Figure 6 shows the pattern of total snowfall anomaly (the amount of snowfall relative to the average amount for 1980 to 1999); the meltwater runoff anomaly (the amount of mass lost to water runoff relative to the 1980 to 1999 average); and the net balance between snowfall and runoff (and evaporation of snow, a minor component of loss) called the surface mass balance (SMB), as calculated by the MAR regional climate model. Highlighted in this graphic are the major ice mass losses of the twelve years preceding 2013. Note that this accounting does not include ice that flows directly into the sea by glacier movement.

Pale by comparison

albedo image

Figure 7. This map shows average summer albedo anomaly for 2013 versus the 2000 to 2011 average, determined by satellite mapping. Data are from the NASA Terra satellite and the MODIS sensor (Moderate Resolution Imaging Spectroradiometer). The data set is the MOD10A1 collection, available from NSIDC. MODIS MOD10A1 data.

Credit: National Snow and Ice Data Center/Jason Box, Geological Survey of Denmark and Greenland (GEUS)
High-resolution image

During summer 2013, the albedo of the Greenland ice sheet surface was higher along the coastal part of the ice sheet than in recent years, indicating less wet snow and snow-free bare ice areas (ablation areas) along the ice sheet perimeter.

Reflectivity is highly variable on an ice sheet: dry snow is the brightest surface cover, above 85% reflectivity, (or, expressed on the 0 to 1 scale, albedo); wet snow has an albedo of about 0.6 to 0.8; coarse wet snow and slush is about 0.4 to 0.5; impurity rich bare ice with no snow cover has an albedo of 0.3; and clear deep water is near 0.10. As fresh snow ages, the grains become coarser and the albedo drops by as much as 10%. Melting in the snowpack has an even more dramatic effect, lowering reflectivity by up to 20%.

With less exposed bare ice near the coasts, the solar reflectance of these regions is higher than the recent average. In the interior, during 2013 summer snowfall events were widely spaced in time over the ice sheet interior, and so the snow surface tended to be older and therefore a bit darker than average.  

More to come

sample images

Figure 8. These images show the new derivative data sets for the Mote Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record data set. The lower left and diagonal panels show average annual and average monthly melt days extent maps, respectively, for the 1981 to 2010 climatology period melt season months April through September. The upper right image shows daily melt extent for 2012, including the two standard deviation range for the 1981 to 2010 period.

High-resolution image

Our next post will examine the early progress of the melt season. In the interim, new supporting data sets and analysis tools have been derived from the melt extent archives that will present a more complete picture of the melt season in 2014.

Several new data sets and graphic upgrades were generated since late September 2013. These changes are summarized in Figure 8 and include an analysis of a 30-year record of daily melt extent spanning the climatological reference period 1981 to 2010, as measured by the Mote melt algorithm (Mote, 2007). The 1981 to 2010 average is shown as a blue dashed line, and the gray area around this average line shows the two standard deviation range of the data. Annual and monthly average melt day maps were also generated, allowing an assessment of the impact of weather events and the trends of melt extent and intensity in various areas.

Resources for analysis of trends and variations for the Greenland Today website will continue to expand as funding permits. We aim to build an interactive analysis tool similar to our Sea Ice Index web pages and to make daily data available as with the Sea Ice News and Analysis web pages. We are presently working on a table of results for the melt days and extents.

References

Fettweis, X., 2007. Reconstruction of the 1979-2006 Greenland ice sheet surface mass balance using the regional climate model MAR. The Cryosphere, 1, 21-40, doi:10.5194/tc-1-21-2007.  See also: https://www.aoncadis.org/dataset/CPL_MAR.html.

Hall, D. K., V. V. Salomonson, and G. A. Riggs. 2006. MODIS/Terra Snow Cover Daily L3 Global 500m Grid. Version 5. Boulder, Colorado USA: National Snow and Ice Data Center.

Mote, T. L., 2007. Greenland surface melt trends 1973–2007: Evidence of a large increase in 2007. Geophysical Research Letters 34, L22507, doi:10.1029/ 2007GL031976.

Acknowledgements

We would like to thank Xavier Fettweis of the University of Liege, Belgium, and Jason Box of the Geological Survey of Denmark and Greenland (GEUS) for their contributions to this post.

 

 

 

Melt calibration, suspension of daily images

The Greenland melt detection algorithm is currently undergoing its annual calibration period. As a result, the daily melt extent mapping image is temporarily suspended. Calibration of the melt detection for each year requires analysis of the springtime snow conditions by a separate program. See our March 13, 2013 post for more discussion of melt calibration.

We will resume the daily image updates in April. A consistent record will be produced later that spans these winter periods retrospectively.

UPDATE, April 30, 2014: We are working to resume image updates by early May. Thank you for your patience.

Late season warmth extends 2013 Greenland melt season…briefly

Greenland’s surface ice melt season reached a peak in late July, coinciding with a period of very warm weather. Greenland’s melt season this year will be closer to average than was 2012, with far less melting in the northern ice sheet and at high elevations. Nevertheless, an all-time record high temperature for Greenland may have been set in 2013.

Overview of conditions

Figure 1. Cumulative Greenland melt days image for 21 July – 19 August (30 days). This period spans the peak melt extents seen this year.

Figure 1. Cumulative surface melt days for July 21 to August 19, 2013 (30 days). This period spans the peak melt extents seen this year. Note that the color scale is 0 to 30 days, rather than 0 to 100 days for the daily figure. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record.
About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

Surface melt on the Greenland ice sheet spread to the northern coastal regions and became especially frequent in the far northeastern corner of the island (Kronprins Christians Land). However, while some high-melt-extent years recently have seen elevations above 2,500 meters (8,200 feet) warm to the melting point, this rarely occurred in 2013, nor was there extensive melt in the northern interior portion of the ice sheet. A small region of the northwestern ice sheet, the drainage areas of Peterman and Humbolt glaciers, saw some inland melting. (However, some of these dark red pixels are mixed land areas, including ice plus rock and permanently frozen ground.) Melt lakes were prevalent along the central western coast in 2013 (as is typical of most seasons) but far less extensive in the northeastern and northwestern regions than in 2012. Melt lakes in Greenland may be seen in NASA Rapid Response-MODIS Arctic Subset images.

Conditions in context

plot

Figure 2a. The graph above shows the daily percent of the Greenland Ice Sheet surface that has shown melt, as of August 19, 2013 (red), along with the daily surface melt extent for 2012 (blue) and the average melt extent for 1981 to 2010 (dashed line). Two peak extent days are noted.

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

Figure2a: Greenland melt extent data comparison for 2012 and 2013 to date. Two peak extent days are noted. Figure 2b:Melt extent map for the peak melt extent day to date this year, July 26.

Figure 2b. The map shows the melt extent for July 26, 2013, the peak melt extent date so far this year. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

The period between July 21 and August 19 (Figure 1) included the greatest percentage of surface melt extent days for Greenland during 2013, peaking at 44% on July 26 (Figure 2b). However, the overall melt extent for 2012 was far greater, exceeding 40% for several weeks (Figure 2a). Data posted by Xavier Fettweis at the University of Liège using a different melt algorithm (see their Figure 4) show that melt day frequency is slightly greater than average for northwestern Greenland near the coast (2 to 8 more melt days than average for the reference period, 1980-2011), and significantly greater than average for northeastern Greenland (8 to 16 days more). According to the MAR (Modèle Atmosphérique Régional) regional climate model, the main melt anomalies in 2013 have occurred along the northeast coast. These anomalies are also indicated in the satellite data, by red pixels in Figure 1. This has been due to the lower winter snowfall than average (resulting in a lower albedo) combined with warmer than average summer temperatures. However, the majority of the ice sheet showed mild to moderately lower-than-average melt duration for this season.

Warm temperatures for Greenland: Maniitsoq, July 30

Figure 3: Weather pattern map for Greenland and northeastern Canada, July 30, 2013 (top) and melt area map for July 31 (below left) and August 1 (below right). Strong southeasterly winds across the western coast brought very warm conditions to that region. The weather graphic was produced by Gorm Larsen for the Danish Meteorological Institute. See: http://www.dmi.dk/nyheder/arkiv/nyheder-2013/8/groenland-saetter-temperaturrekord/. Note that the question of a record warmest temperature for Greenland is still being resolved.

Figure 3: Weather pattern map for Greenland and northeastern Canada, July 30, 2013 (top) and melt area map for July 31 (below left) and August 1 (below right). Strong southeasterly winds across the western coast brought very warm conditions to that region. Note that the question of a record warmest temperature for Greenland is still being resolved. The weather map was produced by Gorm Larsen for the Danish Meteorological Institute.

Credit: National Snow and Ice Data Center/Danish Meteorological Institute
High-resolution image

A pattern of strong southerly winds in late July brought very warm temperatures to southwestern Greenland, possibly the warmest air temperature ever recorded on Greenland since 1958 (when extensive accurate records began). Temperatures at the small hamlet of Maniitsoq were measured at 25.9 degrees Celsius (78.6 degrees Fahrenheit) on July 30. These conditions were in part due to the downhill flow of the air off the western side of the Greenland Ice Sheet. Downhill air flow warms the air as a result of its compression as it goes to lower altitude (foehn or chinook effect). This weather event also led to a large region of melt along the western part of the ice shelf on July 31 and August 1, and the second-highest area of melt this year.

Three summers at Summit

Figure 4. The graph shows Summit, Greenland temperatures for 2011 (purple), 2012 (red), and 2013 to date (green). ||Credit: National Snow and Ice Data Center/Christopher Shuman and Michael Schnaubelt, UMBC JCET and Thomas Mefford, CIRES/NOAA |High-resolution image

Figure 4. The graph shows Summit, Greenland temperatures for 2011 (purple), 2012 (red), and 2013 to date (green).

Credit: National Snow and Ice Data Center/Christopher Shuman and Michael Schnaubelt, UMBC JCET and Thomas Mefford, CIRES/NOAA
High-resolution image

Summit is a research station located at the highest point on the Greenland Ice Sheet, at 3,216 meters (10,551 feet) above sea level. Above-freezing air temperatures were observed there by NOAA sensors for the first time in 2012, although ice cores indicate rare melting events in past centuries. The years preceding and following 2012 show more typical temperature conditions. Figure 4 shows a plot of temperatures recorded at the NOAA observatory at Summit, Greenland. The daily oscillation is a result of a day-night cycle. Although the sun remains above the horizon for much of the summer at Summit, it drops very low in the sky during evening hours and temperatures drop. Research shows that surface melting detectable by remote sensing (see Figures 1 and 2) can begin a degree or two Celsius (2 to 4 degrees Fahrenheit) below freezing due to solar heat absorption by the snow. (Thanks to Chris Shuman, University of Maryland Baltimore County with the support of the NASA Cryospheric Sciences Program, for this part of the discussion.)

Springtime melt in Greenland: Late start, rapid spread

Surface melting of the snow and ice of the Greenland Ice Sheet had a slightly late start, but quickly spread over a significant area, extending over more than 20% of the ice sheet in early June and reaching above 2,000 meters (6,500 feet) elevation in some areas. Small melt lakes have begun to form on the ice sheet, as seen by the new USGS/NASA Landsat-8 satellite.

Overview of conditions

Cumulative melt days for mid-May to mid-June in Greenland using the Mote method of determination of melt from satellite microwave data. Note that the color scale is 0 to 30 days, rather than 0 to 120 days for the daily figure. Lower figure shows the percent of the Greenland ice sheet that had some surface melting for each day of 2013 up to June 19th.

Figure 1. Cumulative surface melt days for mid-May to mid-June in Greenland. Note that the color scale is 0 to 30 days, rather than 0 to 100 days for the daily figure. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data


Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

After the annual re-calibration of the melt algorithm in mid March (see March 18 post), very little melt was detected until May. A few southern coastal areas began melting in mid-May, followed by inland higher-elevation ice and all remaining coastal areas about June 3, when warmer conditions arrived. Surface melting reached the “Saddle” region of the ice sheet (located where the pale bluish band extends from the east to the west coastal zones in Figure 1) on June 11 and 13. Only the central eastern coast remains relatively melt free.

Conditions in context

Figure 2. The graph above shows the daily percent of the Greenland Ice Sheet surface that has shown melt, as of June 18, 2013 (red), along with the average surface melt extent for 1981 to 2010 (blue). ||Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia |High-resolution image

Figure 2. The graph above shows the daily percent of the Greenland Ice Sheet surface that has shown melt, as of June 19, 2013 (red), along with the average surface melt extent for 1981 to 2010 (blue).

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

At this point, the pace of melt is well above average, but well behind the early, intense start seen in the record 2012 season (see February 5 post).

After a spike in melt area in early June, cooler conditions have brought the melt area near the average extent of ~20% of the ice sheet.

 Rising temperatures

Figure 3

Figure 3: These images show temperature anomaly over Greenland at the 850 millibar level (approximately 1,500 meters, or 5,000 feet above sea level)  for May 15 to May 25 (top) and for June 5th to June 15, 2013, compared to the averages from 1981 to 2010. Temperatures were lower than average during May, then shifted to higher than average along the coasts in June.

Credit: Credit: NSIDC courtesy NOAA/ESRL PSD
High-resolution image

Cool conditions in April and May shifted to warmer-than-average weather along both coasts in early June, which initiated more widespread melt on the ice sheet. This shift roughly coincided with a larger change in the Arctic Oscillation from near-neutral conditions to slightly positive, and a shift from generally easterly and northerly winds to southwesterlies. The sea ice on both sides of Greenland remained at near-normal extent through the period.

Landsat 8 Images of early melt lakes

Figure 4. True-color Landsat 8 image of west-central Greenland near 69.9deg N, 51.0 deg W acquired on June 12 (just north of Jakobshavn Isbrae, Landsat acquisition location Path 11, Row 11). The image shows glaciers, coastal bedrock and nunataks, and several small fjords. White areas on the right side of the scene are winter snow (still melting away); light blue and grey areas are exposed ice where the 2012-2013 winter snow has melted away; deeper blue pockets are small incipient melt lakes.

Figure 4. This image from Landsat 8 shows melt ponds forming on the Greenland Ice Sheet. White areas on the right side of the scene are winter snow (still melting away); light blue and grey areas are exposed ice where the 2012-2013 winter snow has melted away; deeper blue pockets are small incipient melt lakes. Glaciers, coastal bedrock, several small fjords, and rocky crags (called nunataks) can also be seen in this true-color Landsat 8 image of west-central Greenland near 69.9 deg N, 51.0 deg W, acquired on June 12, 2013 (just north of Jakobshavn Isbrae, Landsat acquisition location Path 11, Row 11).

Credit: National Snow and Ice Data Center, USGS/NASA Landsat 8
High-resolution image

Melt ponds are already forming in some lower areas of the ice sheet, as shown in Figure 4. Ponds of meltwater on the ice sheet can have a significant impact on ice flow. As the ponds grow and deepen, they can force open cracks in the underlying ice and drain to the base of the ice sheet. This can lubricate the base of the glacier, causing it to flow more rapidly for a brief period. The drained water flows out under the ice sheet, emerging as small streams from beneath the ice at the edge.

This image was acquired by the recently launched USGS/NASA Landsat 8 satellite, using its multi-spectral camera, the Operational Land Imager (OLI). Landsat 8 offers great opportunities for mapping and measurement of the world’s ice and its ongoing changes.  One improvement in the new sensor is the addition of a new spectral band, in the far blue visible range. This band (Band 1) may be useful for mapping lake area and depth. Knowing the total lake volume and rate of lake volume change is an important parameter for characterizing the intensity of the melt season and its potential effect on the rate of ice flow and surface melting for the ice sheet.

A report from the field

Figure 5: This photograph of melt runoff was taken near Kangerlussuaq, Greenland the week of June 17.

Figure 5: This photograph of melt runoff was taken near Kangerlussuaq, Greenland the week of June 17.

Credit: NSIDC courtesy Asa Rennermalm, Rutgers University
High-resolution version

With summer beginning, many Greenland researchers are now in the field, and reporting back on observed surface melting conditions. Thomas Mote from University of Georgia, who is in the Kangerlussuaq area with Asa Rennermalm of Rutgers University, reports indications that there was a fairly warm late winter, a cool spring, and heavy snow in May. This area has experienced strong melting, but much of it is the melting of the late spring snowfall. There is word of a 1-kilometer (0.6 mile) long meltwater lake about 7 kilometers (4 miles) inland on the ice east of Kanger. They did observe some fairly large meltwater streams and moulins.

A darker shade of pale

Figure 6. These color maps show average summer (June, July, and August) albedo for Greenland in 2000 and 2012. Albedo dropped by as much as 0.3 in some areas. The color scale ranges from caramine red (albedo of 1.0) to purple (albedo of 0.0); in the graphics above, the approximate observed range is 0.85 to 0.05. Coastal area albedos are typically below 0.15 (e.g. the western coastal area), and fresh dry powder snow is >0.90 (southeastern ice sheet in the 2000 image). Data are derived from NASA's Terra and Aqua satellites using the Moderate Resolution Spectroradiometer (MODIS) sensors. ||Credit: National Snow and Ice Data Center|High-resolution image

Figure 6. These color maps show average summer (June, July, and August) albedo for Greenland in 2000 and 2012. Albedo dropped by as much as 0.3 in some areas. The color scale ranges from caramine red (albedo of 1.0) to purple (albedo of 0.0); in the graphics above, the approximate observed range is 0.85 to 0.05. Coastal area albedos are typically below 0.15 (e.g. the western coastal area), and fresh dry powder snow is >0.90 (southeastern ice sheet in the 2000 image). Data are derived from NASA’s Terra and Aqua satellites using the Moderate Resolution Spectroradiometer (MODIS) sensors.

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

Surface melting on the ice sheet reduces the reflectivity of the snow, and this change is measured by albedo, the ratio of the amount of light reflected from a surface to the amount of incoming light. Over the past twelve summer seasons, surface melting has increased in Greenland, culminating with last year’s very extensive and intense melt season. Satellite data have been used to track this change in a recently submitted paper by Stroeve et al. (2013, in revision), showing that albedo has dropped by as much as 0.3 (30% reflectivity) in some areas.

Dry cold snow is the most reflective naturally occurring land cover type on Earth, with albedos as high as 0.95, but as melting begins, this drops to 0.70, and continues to drop with increased melt. Very wet snow has an albedo of 0.6 to 0.5, and exposed ice can be as low as 0.3. This darkening of a snow surface with the onset and progression of melt leads to an important climate feedback. With warm conditions, melting and darker snow leads to more sunlight absorbed by the snow, leading to further melting and darkening.

A note on the data

We thank our readers for writing us with useful suggestions to include more historical data on surface melt, as well as other statistical information. We are working to add such information as time and funding permit.

Reference

Stroeve, J., J. Box, Z. Wang, A. Barrett, and C. Schaaf. 2013. Re-evaluation of MODIS Greenland albedo accuracy and trends. Remote sensing of the environment, in revision.

An early spring re-calibration for melt detection

The algorithm for the Greenland Ice Sheet Today daily melt extent has been revised to account for unusually warm winter snow layers and residual meltwater deep in the snow. Meltwater from last summer’s intense melt season did not completely re-freeze through at least mid December. The adjusted algorithm shows greatly reduced melt extent for early 2013. This much lower extent is more consistent with available weather and climate records.

Melt extent and distribution

Figure 1. These images show cumulative melt extent before the algorithm correction (left) and after the correction (right). A few areas indicating one to two days of melting in southeast Greenland remain in the revised map. The red dot shows the location of the Danish AWS.

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

As shown in Figure 1, the adjustment to the algorithm resulted in fewer melt days than previously indicated. The revised image at right shows new surface melting in 2013 in a few small areas along the central southeastern Greenland coast, within the region of earlier spurious melt signals but greatly reduced.

Conditions in context

Figure 2. This image shows air temperature anomaly for Greenland for the period December 2012 to February 2013. Reds and oranges indicate higher than average air temperatures. The temperatures shown are at approximately 1,500 meters (5,000 feet) in altitude, appropriate for coastal Greenland regions. However, central Greenland is above this altitude, and values shown there do not represent the true surface conditions well.

Credit: National Snow and Ice Data Center courtesy NOAA ESRL Physical Sciences Division
High-resolution image

Temperatures in Greenland have been higher than average this winter, with air temperatures near the coast averaging 2.0 to 3.5 degrees Celsius (4 to 6 degrees Fahrenheit) warmer than the 1981 to 2010 average. This has in part been a result of the persistent circulation pattern for the Arctic this winter, characterized by a negative Arctic Oscillation (AO). The AO is a measure of the intensity of the general pattern of low pressure over the northern high latitudes. A negative AO indicates higher-than-average pressures near the North Pole, allowing more frequent southward cold air outbreaks, and more intrusions of warm air masses from higher temperature areas. Despite these anomalously high temperatures along the Greenland coast, temperatures were not high enough to result in melting.

Adjusted algorithm and melt images

Figure 3. This plot shows surface air temperature at a PROMICE on-ice Automated Weather Station (AWS) near the southeastern Greenland ice sheet edge for early 2013. Temperatures did not exceed freezing at this site. Data from PROMICE were provided by the Geological Survey of Denmark and Greenland (GEUS) and are freely available.

Credit: National Snow and Ice Data Center and J. Box, Geological Survey of Denmark and Greenland
High-resolution image

The melt extent algorithm used by Greenland Ice Sheet Today has been overestimating the melt extent, and as a result, daily images posted on this site in February and March may have indicated melt where none occurred. While the algorithm was indicating some coastal melt in February and early March, a comparison with weather data for Nuuk (the Greenland capital city, located along the southwest of the island) and data from the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) suggested these might be spurious melt readings. The local Automated Weather Station (AWS) data from a glacier along the southeastern coast (the Mittivakkat glacier AWS, shown by a red dot in Figure 1; data in Figure 3) indicate that the air temperature did not rise to the melting point (0 degrees Celsius, or 32 degrees Fahrenheit) in February or early March.

Figure 4. A model of the snowpack conditions indicates residual liquid water in the deep snowpack in southeastern Greenland.

Credit: National Snow and Ice Data Center and X. Fettweis, Université de Liège, Belgium
High-resolution image

During this period, starting around mid-February in southeast Greenland, the brightness temperatures in the upper few meters of the snowpack were 2 to 10 degrees Celsius (4 to 18 degrees Fahrenheit) higher than those observed during any other year in the 34-year record (1979 to 2012). While surface melt is not unprecedented in Greenland near the coast in February and March, the totals posted prior to March 14 were a result of these unusual snow temperature conditions, and not ongoing surface melt. This winter has seen unusually warm snow at depth on the ice sheet, following the intense melting that occurred last summer.

The melt detection method, based on passive microwave emissions, is primarily sensitive to near-surface conditions, but has some input from the snowpack down several meters (10 to 20 feet). Heavy snow fell during the relatively warm winter, burying and insulating deeper snow. This contributed to anomalously high temperatures for the uppermost layers of snow this winter. Additionally, models based on snowpack properties suggested that some 2012 meltwater remained unfrozen at 5 meters depth (approximately 16 feet) in mid-December. The model results are consistent with observations from JAXA’s AMSR-2 sensor.

The algorithm was adjusted by combining the trend of observed brightness temperatures with a model of the expected microwave emission in the channels used for melt detection (the SSM/I sensor’s 37 GHz Horizontal polarization channel). This adjustment is generally performed every year in March to calibrate the melt detection thresholds. However, because of the unusual condition of the snowpack, the adjustment needed to be made much earlier than ever before.

Further information

Fettweis, X., M. Tedesco, M. van den Broeke, and J. Ettema, 2011. Melting trends over the Greenland ice sheet (1958-2009) from spaceborne microwave data and regional climate models. The Cryosphere 5, 359-375, doi: 10.5194/tc-5-359-2011.

Programme for Monitoring of the Greenland Ice sheet (PROMICE)

An intense Greenland melt season: 2012 in review

Greenland’s surface melting in 2012 was intense, far in excess of any earlier year in the satellite record since 1979. In July 2012, a very unusual weather event occurred. For a few days, 97% of the entire ice sheet indicated surface melting. This event prompted NSIDC to build this Web site, with the help of two prominent experts on Greenland surface melting (Dr. Thomas Mote of University of Georgia, and Dr. Marco Tedesco of CUNY).

The Greenland Ice Sheet contains a massive amount of fresh water, which if added to the ocean could raise sea levels enough to flood many coastal areas where people live around the world. The ice sheet normally gains snow during winter and melts some during the summer, but in recent decades its mass has been dwindling. For more information about the significance of the Greenland Ice Sheet and its surface melt, see About the Greenland Ice Sheet.

Warm conditions in 2012 were caused by a persistent high pressure pattern that lasted much of the summer. Since September, temperatures have remained warmer than average, but dropped well below freezing as autumn and winter arrived. We review the year’s events, and introduce some general characteristics of the Greenland ice sheet.

Overview of conditions

Figure 1. The number of melt days in 2012 on the Greenland Ice Sheet exceeded 120 for low elevation areas along the southwestern coast, and values above 100 days were seen in the far north and southeastern coastal areas. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

Figure 1 shows the cumulative number of days of melt occurrence for 2012. The number of melt days in 2012 on the Greenland Ice Sheet exceeded 120 for low elevation areas along the southwestern coast, and values above 100 days were seen in the far north and southeastern coastal areas as well.

Overall, melt extent was the largest in the satellite record since 1979, and melting lasted almost two months longer than average. This was the first year in the satellite record that the entire ice sheet experienced melt at some point in the season.

During a peak melt event in July, even the summit areas of the ice sheet, nearly two miles above sea level, saw snowmelt conditions. While this has been observed in ice cores a handful of times in the past 1,000 years, it had not previously occurred in this century.

Conditions in context

Figure 2. The graph above shows the daily extent of melt during 2012 on the Greenland Ice Sheet surface as a percentage, compared to the average from 1981 to 2010. Data are from the Greenland Daily Surface Melt 25km EASE-Grid 2.0 Climate Data Record. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
High-resolution image

Greenland’s 2012 melt season started early, surpassing the 30-year average for melt-covered area in mid-May, and remaining far in excess of typical conditions for June, July, and through mid August. For the peak melt days in early July and again in early August, more than 70% of the surface of the ice sheet experienced some melt, and the peak melt event on July 10 to 11 occurred over 97% of the ice sheet.

The overall pattern of melt is closely related to elevation. At the edges of the ice sheet, near the coast, melt is far more frequent. With increasing elevation, up to 2,000 meters (6,300 feet) or so, the number of melt days decreases from tens of days to just a few days. Above 2,500 meters, melt is rare, and in most years a large region of central and northern Greenland (up to 3,100 meters above sea level, or approximately 10,000 feet) sees almost no surface melt.

During 2012, a significant increase in melting days was seen at higher elevations as well, causing surface melting to percolate into older snow below and refreeze. Runoff of water from the ice sheet was intense. In one case, bridges and other structures adjacent or crossing a usually small melt-fed river, the Watson River near Kangerlugssuaq, were destroyed in mid July.

2012 compared to previous years

Figure 3. The image above shows the average cumulative melt days for the Greenland Ice Sheet for the period 1979 to 2007. Oranges and reds indicate greater numbers of melt days, while blues and greens indicate no or low numbers of melt days. Note: This image uses a different ice sheet mask than Figure 1. As a result, some coastal areas showing melt in Figure 1, such as the northern coast, are masked out in Figure 3. Data are from Greenland Ice Sheet Melt Characteristics Derived from Passive Microwave Data, from the Scanning Multi-channel Microwave Radiometer (SMMR) and the Special Sensor Microwave/Imager (SSM/I) instruments.

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

Figure 3 is a plot of the average annual number of melt days, for the period 1979 to 2007. These data come from a 2008 study of Greenland melt by Abdalati et al. based on the Scanning Multi-channel Microwave Radiometer (SMMR) and the Special Sensor Microwave/Imager (SSM/I) instruments, as part of the Program for Arctic Regional Climate Assessment (PARCA). These data provide a snapshot of past conditions over a longer time period.

The plot shows a more typical pattern of melt occurrence and number of melt days. A comparison with Figure 1 illustrates the extreme nature of the 2012 melt. Melt in 2012 was far more frequent and extensive along the northern west coast, the far north, and the southeast and southwest coastal areas of Greenland, as well as the almost unprecedented areas at high elevation. However, intense melt years have been the rule since 2006, particularly in 2007 and 2010.

The upward march of melt

Figure 4. This illustration shows a generalized cross-section of glacier facies, zones with distinct physical characteristics resulting from the conditions that formed or changed the snow. The snow cover is completely stripped away in the ablation facies. The entire year’s accumulation is raised to the melting point and wetted in the soaked facies. In the percolation facies, the annual increment of new snow is not completely wetted nor raised to the melting point, and the amount of percolation decreases with altitude, becoming negligible at the dry snow line. Little or no melt occurs in the dry snow facies.

Credit: National Snow and Ice Data Center/C.S. Benson
High-resolution image

The perennial pattern of melt seen in Figure 3 has had a large impact on the character of the ice sheet. Figure 4, from Benson 1996, is a summary of what happens in the snow and ice during a summer melt season. The term facies refers to areas or zones of the ice with distinct characteristics that provide clues to the conditions that formed or changed them.

At low elevations, all the winter snow is melted away early each year, and bare ice is exposed and melted. This is the ablation zone, where old ice flowing out from the center of the sheet is melted as part of the annual melt season, and the water flows over the surface to the coast. Above this, there is a zone where annual melt may or may not remove all of the winter’s snow. If the melt completely saturates the snow with water, lakes and rivers are seen on the ice surface, forming the saturation zone or wet snow zone. Where the surface melt water drains into the snow but remains more or less in place and re-freezes as an ice layer, we get a percolation zone. Above this is the dry snow zone where melt rarely occurs.

A major signal of climate change for Greenland is the steady climb of these facies uphill as melt seasons and summer temperatures increase. The changes in facies also pre-condition the surface of the ice sheet for even more melting.

Not-so-arctic weather

Figure 5. This image of Greenland summer 2012 air temperature anomalies at the 925 hPa level (about 3,000 feet above the surface) shows that all of Greenland experienced warmer than average temperatures, with the strongest warming along the west coast. Temperatures are compared to the 1981 to 2010 average.

Credit: National Snow and Ice Data Center, from NOAA/ESRL Physical Sciences Division
High-resolution image

Summer warmth this year in Greenland was intense and widespread. In areas already prone to summertime melt, the period June through August of 2012 was more than 2 degrees Celsius (4 degrees Fahrenheit) warmer than the average for 1981 to 2010, and greater than 1.5 Celsius (3 degrees Fahrenheit) for nearly the entire ice sheet. This resulted from a very persistent high pressure ridge that dominated the weather, creating clear skies, light winds, and low precipitation.

Edward Hanna at the University of Sheffield and colleagues recently published a study of Greenland temperatures based on weather station data. They found warming to be much stronger on the west side of Greenland than on the east since 1991. The data from 1991 to 2012 show that some locations in western Greenland have warmed 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) during summer, while some locations along the west and northwest coasts of Greenland warmed as much as 10 degrees Celsius (18 degrees Fahrenheit) during winter.

At present, the Greenland Ice Sheet is in its winter mode. As the daily images show, it is currently exhibiting little or no melt as would be expected for this time of year. NSIDC will continue to post daily image updates throughout the 2013 melt season, and provide periodic analysis as conditions warrant.

References

Benson, C. S. 1996. Stratigraphic studies in the snow and firn of the Greenland ice sheet. U.S. Army Corps of Engineers: Snow, Ice, and Permafrost Research Establishment Res. Rep. 70.

Hanna, E., S. H. Mernild, J. Cappelen, and K. Steffen. 2012. Recent warming in Greenland in a long-term instrumental (1881–2012) climatic context: I. Evaluation of surface air temperature records. Environmental Research Letters 7, no. 4, doi:10.1088/1748-9326/7/4/045404.

Tedesco, M.,  X. Fettweis, T. Mote, J. Wahr, P. Alexander, J. Box, and B. Wouters. 2012. Evidence and analysis of 2012 Greenland records from spaceborne observations, a regional climate model and reanalysis data. The Cryosphere Discuss., 6, 4939–4976, doi:10.5194/tcd-6-4939-2012.