Greenland’s three melt surges rival 2012 record

Greenland’s 2016 melt season started fast. It maintained a brisk pace with three extreme spikes in areas of melt through June 19. On June 9, Nuuk, the capital, reached the warmest temperature ever recorded for the month of June anywhere on the island, 24 degrees Celsius (75 degrees Fahrenheit).

Overview of conditions

melt curve and area up to June 19

Figure 1a. These maps show the cumulative melt day for the Greenland Ice Sheet as of June 19, and melt day anomaly relative to the 1981 to 2010 average for 50 days leading up to June 19. Below, a chart shows the daily melt extent for the year; the 2012 melt area curve is shown for comparison.

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

2012, 2013, 2014, 2015 melt trends

Figure 1b. These maps show the melting trends for 2012, 2013, 2014, and 2015, with the same processing and reference period as the upper right map in Figure 1a. Each map shows the 50 days leading up to June 19.

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

Surface melting on Greenland’s Ice Sheet proceeded at a brisk pace, with three spikes in the melt extent in late spring. At this point, the pace rivals but is slightly behind the record surface melt and runoff year of 2012 (record since 1979), although ahead of the three preceding seasons. Melting in 2016 is especially severe in southwestern Greenland, and moving beyond the 1981 to 2010 rate everywhere except the northwestern coast (northern Melville Coast). This has led to the early formation of melt ponds along the southwestern flank of the ice sheet and early run-off from the ice sheet.

Conditions in context

Figure 2a. The plot shows sea level equivalent mean pressure departure from the average from May 1 through June 19. The reference period is 1981 to 2010. What is the plot showing? An analysis usually goes here. Figure 2b. The plot shows temperature departure from average at the 700 millibar level (about 10,000 feet above sea level) from May 1 through June 19. The reference period is 1981 to 2010. What is the plot showing? An analysis usually goes here. ||Credit: National Snow and Ice Data Center/NOAA ESRL Physical Sciences Division High-resolution image

Figure 2a. The plot shows sea level equivalent mean pressure departure from the average from May 1 through June 19. The reference period is 1981 to 2010.
Figure 2b. The plot shows temperature departure from average at the 700 millibar level (about 10,000 feet above sea level) from May 1 through June 19. The reference period is 1981 to 2010.
Warmer than average conditions (1.5 to 2 degrees Celsius, or 3 to 5 degrees Fahrenheit) were seen in the northern and southern areas of the ice sheet.

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

A pattern of higher pressure over central Greenland continued the trend of southerly wind influx along the southwestern coast, consistent for the spring period. This trend was also observed in the early April spike in ice surface melt area. Temperatures were mildly warmer than average (0.5 to 2 degrees Celsius or 1 to 3.6 degrees Fahrenheit) over most of coastal Greenland but slightly below average in the interior.

Air temperatures in Nuuk, the capital of Greenland, reached 75 degrees Fahrenheit on June 9, marking the highest temperature ever recorded on the island for June. When air flows downhill, air compresses and warms. The persistent high pressure pattern in northeastern Greenland forced downsloping winds, and with a low pressure center to the south of Greenland, temperatures rose. Such conditions are responsible for record or near-record warm temperatures along western Greenland.

Jet stream meanders led to 2015 melt pattern 

Figure 3. Top figure (a) shows the air pressure pattern over Greenland and surrounding regions for July 2015, based on the altitude of 500 hectopascal pressure level (high equals high pressure). Lower right map (b) shows the net runoff as it compares to the mean value of the run-off for that region (e.g., 2 means twice as much as average; -2 means one-half of average). Lower left charts (c) show the temperature, albedo, and runoff trends since 1950. The upward trend for these three regions is related to the tendency for a persistent high pressure ridge north of Greenland, or a cut-off high. || Credit: Tedesco et al., Nature Communications|| High-resolution image

Figure 3. Top (a) air pressure pattern over Greenland and surrounding regions for July 2015, based on the altitude of the 500 hPa pressure level (high = high pressure). Lower right (b), a map of net runoff scaled by the average variability (i.e., the standard deviation of run-off for the 1981 to 2010 period) of the run-off for that region (e.g., ‘2’ means two standard deviations above average ; -2 means two standard deviations below average). Lower left (c) a series of charts showing the trends since 1950 for temperature, albedo, and runoff, again scaled in units of standard deviation. The upward trend for these three regions is related to the tendency for a persistent high pressure ridge north of Greenland, a ‘cut-off high’.

Credit: Tedesco et al., Nature Communications
High-resolution image

Wind patterns and weather control the amount of melting on Greenland, and therefore the amount of ice that is added to the sea each year by meltwater runoff. Using sophisticated climate models and past weather data that can reproduce the past conditions over the Greenland, a new study has shown that in 2015 Greenland’s weather changed to favor more melting in the northern part of the island (see GT November 2015 post). In earlier years, high-pressure systems over Greenland promoted increased melting in its southwestern portion. In 2015, a persistent high-pressure ridge set up further north, over the Arctic Ocean and the northern half of the island, pulling warm air northeastward over the southern half of Greenland, and shifting the areas of frequent melting northward. Snowfall increased in the south. The high-pressure system in 2015 ‘detached’ from the jet stream (e.g., a ‘cut-off high’ or ‘blocking high’) and became disconnected from the jet stream flow. Disconnected high or low pressure areas are more common when the meanders of the jet stream are more pronounced, pushing long loops high into the Arctic or southward into temperate areas. The exceptional 2015 summer Arctic atmospheric conditions saw a record high latitude of the jet stream flow and strong north-south winds (rather than east-west winds) in the North Atlantic and Baffin Bay areas.

Tough time for research teams in Greenland

Top, melt ponds in southwestern greenland; bottom, an ice core shows an increased density of Greenland's snow

Figure 4. Top, melt ponds formed early in the 2016 season in southwestern Greenland; Bottom, a core of the upper snow layers allows MacFerrin and colleagues to observe past melt layers. Increased density of Greenland’s snow is due to increased melting and re-freezing. Credit: Mike MacFerrin, Cooperative Institute for Research in Environmental Sciences (CIRES)

Greenland’s variable melt affected science teams working high on the ice. “As we crossed Greenland’s interior this spring, melt hounded us most of the way,” said CU Boulder researcher Mike MacFerrin. “As temps soared near freezing, snow began melting on our drills, causing them to occasionally freeze solid in boreholes as we worked. One of our stuck drills required 30 gallons of boiling water, aircraft cable, and a snowmobile to finally retrieve,” he said. Toward the end of their trip, the team worked through slushy days with nighttime temperatures only dropping to -1 degrees Celsius. “We got our work done, but the early-season melt tossed us curve balls along the way,” he added.

MacFerrin and the rest of the NASA-funded “FirnCover” team are primarily tasked with measuring firn compaction—the rate snow slowly compresses into glacial ice—which is crucial to accurately map Greenland and Antarctica’s changing masses. “The increases in high-elevation melt complicate everything we’re trying to measure,” MacFerrin said. “It’s the biggest factor reshaping the interior of Greenland’s snow and firn. Enhanced melt over the past ten to fifteen years has affected every site we visit.” Computer models simulate compaction, but most of the models were not intended to capture the types of rapid changes currently observed across Greenland. “We’re doing what we can to account for it, but we feel like we’re barely keeping up,” he said.

Further reading

Arctic cut-off high drives the poleward shift of a new Greenland melting record
The 2016 Greenland ice sheet SMB
Polar Portal’s Greenland surface conditions for June 2016
PROMICE: Programme for Monitoring of the Greenland Ice Sheet

To read more about the FirnCover team and their work, please visit their blog “Under the Surface of the Greenland Ice Sheet.”

Early start to Greenland Ice Sheet melt season

For six days in early April, unusual weather patterns produced an early season melt event on the Greenland Ice Sheet, covering up to 10 percent of its surface area. Such an event is unusual but not unprecedented; the record surface melt season of 2012 began in a similar manner. Local meteorological records were set in southwestern Greenland towns and at several ice sheet weather stations.

Overview of conditions

Maps of melting and graph of melting extent

Figure 1a. The maps show the melt area pattern on April 11 (left) and cumulative days of surface melting through April 17 (right) on the Greenland Ice Sheet. 
Figure 1b. The graph above shows the daily extent of melt during 2016 through April 17, 2016 on the Greenland Ice Sheet surface, as a percentage (red line). 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 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

An early melt event occurred on April 10 through April 15, encompassing the central western and southeastern Greenland coastal areas. The event was a result of a large pulse of mid-Atlantic air moving northward, bringing record warm air to the entire ice sheet and rain along the western coast. Approximately 10 percent of the ice sheet surface melted on April 11, dropping to 5 percent on April 12 and less on later days. A melt event of similar magnitude occurred on April 6 to 9 of 2012, which became the current record surface melt and melt-runoff season for the satellite era (since 1978). (These values and dates are slightly different from those reported in other news releases, because they are based on different snowmelt mapping methods). Early melt events are important as they lower the surface albedo by increasing the snow grain size. A lower albedo allows for more absorption of the sun’s energy, fostering more ice melt.

Conditions in context

temperature and wind anomaly plots for April

Figure 2a. The plot shows average monthly air temperature anomaly for April 11 to 12 at the 700 millibar level (about 10,000 feet altitude). Anomalies are compared to the 1981 to 2010 average conditions for the month. Higher than average temperatures were present inland as well as around the southeastern coast.
Figure 2b. The plot shows average monthly wind anomaly for April 9 to 15, 2016 over Greenland. Anomalies are compared to the 1981 to 2010 average. The plot shows the strong northward wind along the west coast. 

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

temperature map of northern hemisphere

Figure 3: The map shows average temperatures for the Northern Hemisphere between January and March 2016 at the 925 millibar level (approximately 2,500 feet altitude).

Data are from ESRL NCEP weather reanalysis. Credit: Brian Brettschneider
High-resolution image

A surge of warm, moist air caused the early melt event. The air mass moved almost due north from the mid-Atlantic region along the western coast of Greenland, and then eastward across the ice sheet. On April 10, melting was confined to a narrow region of the southwestern coast, which spread on April 11 inland along the west side of the ice sheet and to the southeastern coast. During the last days of the melt event, melting was confined to the far southern coasts of the island. Conditions were warm throughout Greenland. Near-record April temperatures in Kangerlugssuaq reached 17.8 degrees Celsius (64 degrees Fahrenheit) and -6.6 degrees Celsius (20.1 degrees Fahrenheit) at the Summit research station. Data from NCEP/NCAR atmospheric reanalysis show that during the first three weeks of April near-surface air temperatures were 4 to 8 degrees Celsius (7 to 14 degrees Fahrenheit) above average over the entire ice sheet, with the largest departures over northwest Greenland. During the melt event, temperatures rose up to 16 degrees Celsius (29 degrees Fahrenheit) above average for this time of year.

These warm April conditions follow on the warmest winter (January 1 to March 31, 2016) recorded for the Arctic. Large areas of the Arctic reported the warmest conditions in 67 years of weather model data, including the northern half of the Greenland Ice Sheet, much of the central Arctic, southern Alaska and the Canadian Rockies, and parts of central Siberia. The north-central Pacific and northern Atlantic saw temperatures among the lowest on record for that period.

How’s the snow this year in Greenland?

Figure 4: This map of Greenland shows the total precipitation (in mm of water equivalent) from September 1, 2015 to April 16, 2016. The hatched area indicates regions with near-average snowfall levels. Anomalies are compared to the 1981 to 2010 average. ||Credit, MAR3.5.2 and X. Fettweis. |High-resolution image

Figure 4: This map of Greenland shows the total precipitation (in millimeters of water equivalent) from September 1, 2015 to April 16, 2016. The hatched area indicates regions with near-average snowfall levels. Anomalies are compared to the 1981 to 2010 average.

Credit: MAR3.5.2 and X. Fettweis, University of Liège 
High-resolution image

Fall, winter, and early spring snowfall in Greenland is near-average, except in South Greenland where anomalies are higher than the interannual variability. Above average snow totals occurred in the southeast while snowfall was below average along the southern western coast where the early melt event occurred. Last season’s snow can absorb much of this early meltwater. However, a lower than normal winter snowpack combined with this early melt event favor higher summer melt in this area because bare ice below the winter snow cover should appear sooner. Snowfall also plays an important role in the albedo of the ice sheet. New snow has an albedo between 0.85 and 0.90, absorbing only 10 to 15 percent of the incoming solar energy, but as warm conditions and surface melting continue, the surface darkens as the snow becomes coarse and wet.

Further reading

The 2016 Greenland Ice Sheet SMB simulated by MARv3.5.2 in real time
Polar Portal: Unusually Early Greenland Melt
Polar Portal: Monitoring ice and climate in the Arctic (GEUS, DMI, DTU) c/o
Dr. Jason Box, Geological Survey of Denmark and Greenland (GEUS) Greenland Melting
PROMICE: Programme for Monitoring of the Greenland Ice Sheet

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.

Bringing the high heat to the upper inside corner

Surface melting was significantly more frequent and more extensive than average on the Greenland Ice Sheet in July, especially around the northwestern coast. July also saw high air pressure over the entire island and warmer-than-average temperatures in the northwest. This warmer summertime pattern, combined with lower winter snowfall patterns, resulted in a large mass loss from the ice sheet for the summer to date.

Overview of conditions

melt extent images and chart

Figure 1a. The maps show the cumulative days of surface melting (left) and anomalies in the number of melt days (right) for July 2015 (31 days) on the Greenland Ice Sheet. Anomalies are compared to the period 1981 to 2010.

Figure 1b. The graph above shows the daily extent of melt during 2015 through July 31, 2015 on the Greenland Ice Sheet surface, as a percentage (red line). 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 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

The surge in surface melt extent for the Greenland Ice Sheet that began in late June continued through much of July, with melt extent through mid-month not far from two standard deviations above the average for the 1981 to 2010 reference period, and peaking above two standard deviations during the first few days of July. By the last week of the month, overall melt extent had fallen below average.

Broad areas of the far northern ice sheet and the northwestern Melville Coast experienced frequent surface melting. A somewhat unusual pattern occurred in the south, with more melt days than average near the ice sheet ridge crest (center) and coastline, and below-average melting in mid-elevation areas. The pattern could be explained by calm winds near the ridge crest, permitting surface melt, and stronger winds along the flanks, or by differences in cloud conditions. A similar pattern is seen in a model of surface melting based on weather conditions (see Dr. Xavier Fettweis’ Web page).

Conditions in context

temperature and pressure plots

Figure 2a. The plot shows average monthly air temperature anomaly for July 2015 at the 700 millibar level (about 10,000 feet altitude). Anomalies are compared to the 1981 to 2010 average conditions for the month. While the northwestern corner of the island was warmer than average, the southeastern coast was slightly cool.

Figure 2b. The plot shows average monthly sea level pressure anomaly for July 2015 over Greenland. Anomalies are compared to the 1981 to 2010 average. High pressure (on average) covered the entire island, and sunny conditions were reported by researchers in the field on the coasts.

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

Greenland’s temperature pattern is almost always a bull’s-eye pattern, warmer around the coast and significantly colder near the center of the ice sheet. This pattern is driven by the high elevation difference between coast and summit. For this reason, we look at anomaly, or the deviation from the average pattern, to help see the weather characteristics of the month. In July, the anomaly showed a strong gradient from northwest to southeast, with conditions up to 3.5 degrees Celsius (6 degrees Fahrenheit) above average near Qaanaaq (Thule) in northwest Greenland, and about 1.5 degrees Celsius (3 degrees Fahrenheit) below average near Helheim Glacier in the southeast. The temperature pattern is consistent with a pressure pattern that has higher-than-average air pressure centered over the island for the month. A tendency toward clear skies and southerly winds along the northwestern coast is associated with high pressure over central Greenland.

The NAO (North Atlantic Oscillation) and AO (Arctic Oscillation) remained in a mildly negative index pattern throughout July.

Running a deficit

surface mass balance images and graphs

Figure 3. The top images show where Greenland has lost ice due to low snow input and melting runoff combined, shown as change in the net amount of ice thickness (a), and how the pattern of loss from autumn 2014 through July 2015 compares with the typical range, and with the recent record loss year of 2012 (b). The difference, or balance, between snow input and melt run-off for glaciers and ice sheets is called the surface mass balance (SMB). For the entire island, the net surplus or deficit is measured in gigatons (Gt) or gigatons per day (Gt/day). The bottom maps show the total snowfall mass in kilograms per meter squared (c), and the anomaly of snowfall for the past winter season in the same units (d). Divide the values in c and d by ~5 to get pounds per square foot.

Credit: NSIDC courtesy J. Box/X. Fettweis
High-resolution image

The sharp increase in surface melt extent (and estimated melt runoff) in July resulted in large ice mass loss rates. Although 2015 is not at satellite-era record levels (set in 2012), there was a large rate of loss overall. A combination of low snowfall in the past winter season and warm temperatures with extensive melting resulted in a large loss of ice from the ice sheet in the northwest. Some areas in the southern one-third of the ice sheet have less loss than average. Greenland typically loses mass due to melt runoff through the summer, although in recent years both low snow and runoff, and an increase in glacier outflow (not shown here) have combined to significantly shrink the thickness of the ice sheet, contributing to sea level rise.

Water-soaked: continued from June 15th

Figure 4.

Figure 4. Left, map of Greenland showing areas mapped by Operation IceBridge as firn aquifer. The blue star is the location of the field expedition study area. Right, NSIDC scientist Dr. Lora Koenig holding a section of ice core, containing both ice and water, used to determine the volume of water in the aquifer.

Map credit: L. Koenig, NSIDC. Photo credit: Clément Miège.
High-resolution image

The high pressure over Greenland for much of July led to very good conditions for field work, bringing sunny skies to southeast Greenland. While melt area dropped below average overall for Greenland late in the month, melting was still frequent along the coastal southeast. The Greenland aquifer field team (a joint NSF/NASA research project) conducted a field measurement program to determine how the firn aquifer level and volume fluctuates through time (see our post for June 15, 2015, and the Earth Observatory Greenland Aquifer Expedition site).

As warming conditions continue over the Greenland Ice Sheet, melt is extending further inland, increasing the extent of water-soaked snow at depth (called the firn aquifer). The aquifer level is also rising towards the surface in the interior of the ice sheet. Some drainage, locally lowering the aquifer level, has been observed toward the coast. To date there are just two ice cores that can be used to determine the volume of water in the aquifer. These suggest that the total volume of water in the aquifer has not changed significantly between 2013 and 2015. Airborne radar from Operation IceBridge from 2011 to 2013 suggests that the volume of the aquifer is likely increasing inland and perhaps decreasing towards the coast.

Fly-over tour of the Greenland melt lake region

melt lakes image

Figure 5. Imagery from the NASA/USGS Landsat 8 satellite on July 12, 2014 shows melt lakes on the surface of the ice sheet in southwest Greenland. Click on the image to watch a narrated animation of the melt lakes image.

Credit: Allen Pope, NSIDC/NASA Goddard Space Flight Center
View the animation

A mock aerial tour video, created by NASA’s Goddard Data Visualization group, highlights the importance of surface meltwater lakes in western Greenland and describes the goals of mapping lake depths from space. NSIDC’s Dr. Allen Pope narrates.

Meltwater on the surface of the ice sheet can drain through the ice and accelerate the flow of ice by partially lifting the ice sheet off the bedrock and gravel base (see Zwally et al. study for further reading). Landsat 8 satellite imagery from last July helps show the many melt lakes that typically pock the surface of the ice sheet in summer.

References

Zwally et al., Surface melt-induced acceleration of Greenland Ice Flow, Science, doi: 10.1126/science.1072708.

Summer heat hits cold ice sheet

Warm conditions arrived on the Greenland Ice Sheet in late June, causing a sudden spike in melting that increased in early July and led to a sharp reduction in surface albedo (brightness of the snow). However, as of mid-July surface melt remained less extensive than during 2012, the record melt summer.

Overview of conditions

surface melt extent

Figure 1a. The maps show the cumulative days of surface melting (left) and anomalies in the number of melt days (right) for June 2015 (30 days) on the Greenland Ice Sheet. Anomalies are compared to the period 1981 to 2010. 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 area graph

Figure 1b. The graph above shows the daily extent of melt during 2015 through July 11, 2015 on the Greenland Ice Sheet surface as a percentage (red line). The blue line shows the melt extent percentage for the record-setting 2012 summer, for comparison. 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 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

Despite getting off to a slow start this summer, after an unusually cold period (3 degrees Celsius, or 5 degrees Fahrenheit below the 1981 to 2010 average for west Greenland), sunny and sharply warmer conditions during the second half of June favored extensive melting along the western coast of Greenland, pushing the melt day count well above the 1981 to 2010 average by the end of the month. As of the end of June, both the north and southeast ice sheet areas still had significant areas where the number of melt days was below average; however, these areas saw intense melt for several days during the first half of July.

Conditions in context

air temperature anomaly plot

Figure 2a. The plot shows average monthly air temperature anomaly over Greenland for June 2015 at the 700 millibar level (about 10,000 feet altitude). Anomalies are compared to the 1981 to 2010 average. Temperatures were near average over many areas of Greenland for the month of June, but below average in the high Summit area.

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

sea level pressure anomaly plot

Figure 2b. The plot shows sea level pressure anomaly over Greenland for June 10, 2015, during the period of rapid increase in surface melt extent. Anomalies are compared to the 1981 to 2010 average.

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

Temperatures at the 700 hPa level (about 10,000 feet altitude) for the month of June overall were near average over much of coastal Greenland, and below average at the summit area (2 degrees Celsius, or 4 degrees Fahrenheit, below the 1981 to 2010 average). However, for the latter part of the month, and extending into mid-July, temperatures were everywhere markedly higher than average. Along the central western Greenland coast, temperatures rose to 2.5 degrees Celsius (5 degrees Fahrenheit) above the average, and 1.5 degrees Celsius (3 degrees Fahrenheit) above average along the northern and northeastern coasts. These warm conditions are linked to above average sea level pressures over Greenland from mid-June to mid-July.

The major circulation patterns governing climate variability, the NAO (North Atlantic Oscillation) and AO (Arctic Oscillation) shifted during the month of June and into July to a negative index pattern, meaning that circulation in the North Atlantic and Arctic are described by a more sinuous, weaker polar jet stream, and generally more mixing of air between polar and arctic latitudes.

View a plot of air temperature anomalies for June 10 to July 10

View a plot of sea level pressure anomalies for June 10 to July 10

View an illustration of North Atlantic Oscillation positive and negative modes

View an illustration of Arctic Oscillation positive and negative modes

Lower, upon reflection

albedo graph

Figure 3. The graph shows albedo variations over the annual cycle for the Greenland Ice Sheet. The black line shows the 2015 trend, which briefly surpassed the record-setting 2012 season. Data are from the MODIS/Terra Snow Cover Daily L3 Global 500m Grid albedo product.

Credit: Jason Box/GEUS
High-resolution image

Reflectivity of the ice sheet, as measured by the climate variable albedo, dropped sharply during the second half of June as the ice sheet surface melt extent rapidly increased. By early July, the albedo was the lowest in the 16-year MODIS record used for comparison, including the summer of 2012, which set a record for high melt extent in the modern satellite era. The trend toward lower albedo over the period of satellite observations is due to a combination of warming, greater melting on the ice and possibly an increase in soot and dust deposited on the ice sheet. Warm conditions, near the melting point but still below it, can cause a snowpack to evolve more rapidly toward rounder snow grains. The net effect of this rounding is that the snow absorbs slightly more light, that is, it becomes a bit darker. For the regions of melting, wet snow absorbs much more light than dry snow, reducing albedo.

Clear and sunny

MODIS image of the Arctic

Figure 4. This Moderate Resolution Imaging Spectroradiometer (MODIS) true-color Arctic mosaic image for July 7, 2015 shows surface melting on the northwest coast of Greenland as well as areas of surface melt on Arctic sea ice.

Credit: Land Atmosphere Near-Real Time Capability for EOS (LANCE) System, NASA/GSFC
High-resolution image

A MODIS daily mosaic image of the Arctic for July 7, 2015 shows clear skies over Greenland, associated with a strong high pressure pattern, and areas of extensive surface melting along parts of the the western (upper left) and northern coastal areas of the ice sheet (grey-blue regions around the perimeter of the ice sheet). The image also shows areas of smoke haze above the sea ice in northern Siberia. Farther afield, note the much darker surface of the Arctic sea ice cover relative to the higher central areas of Greenland. Being at sea level, the entire sea ice surface melts, usually by late June. Areas of significant surface melt ponding on the sea ice have a more bluish cast.

Long-term circulation trends favor increased melt

sea level pressure plots

Figure 5. These plots show seasonal trends in sea level pressure for the Northern Hemisphere from 1979 to 2014. Data are from the NCEP/NCAR Reanalysis. Areas outlined in dark green are statistically significant.

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

Sea level pressure has increased over Greenland and the central Arctic Ocean north of the Canadian Arctic Archipelago during summer in recent decades. This trend favors warmer air temperatures and enhanced melting over the Greenland Ice Sheet. In addition, this pattern, when it occurs together with below normal sea level pressure over Eurasia, favors increased sea ice melt as well as increased ice transport through Fram Strait. The combination has been implicated in the accelerated rate of sea ice loss in recent years. A recent study suggests that earlier spring snowmelt may be contributing to the predominance of this summer atmospheric circulation pattern (see our July 8 Arctic Sea Ice News and Analysis report). However, another study suggests a link between tropical sea surface temperatures. Regardless of the mechanisms driving the trend towards a more negative NAO pattern in summer, this pattern appears to be related to increased temperatures that promote more summer melt.

References

Matsumura, S. et al. 2014. Summer Arctic atmospheric circulation response to spring Eurasian snow cover and its possible linkage to accelerated sea ice decline, J. Climate, doi:10.1175/JCLI-D-13-00549.1.

Ding, Q. et al. 2014. Tropical forcing of the recent rapid Arctic warming in northeastern Canada and Greenland, Nature 509, doi:10.1038/nature13260.

Cold and snowy spring slows start of Greenland melt

The Greenland Ice Sheet began 2015 (January 1 to May 31) with cooler-than-average conditions and higher-than-average snowfall accumulation, related to a near-continuous positive North Atlantic Oscillation (NAO) index pattern through the period. Surface melting was limited to just a few of the southern coastal fjord areas. The reduced melting and high snowfall has led to higher surface albedo (a whiter surface) near the coast than is typical for May. However, as June has unfolded, surface melt extent has increased to near-average levels. Most of this new melt extent is in the central western section near Jacobshavn. The albedo trend along the coastal ice has reversed, consistent with melt onset. However, below average temperatures persist into early June.

Overview of conditions

melt days and melt day anomalies images

Figure 1. The maps show the cumulative days of surface melting (left) and anomalies in the number of melt days (right) for May 2015 (31 days) on the Greenland Ice Sheet. Anomalies are compared to the period 1981 to 2010. 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

The number of surface melt days along the Greenland coast was well behind the levels typical of this time of year (relative to 1981 to 2010) for the entire southern rim of the ice sheet. Surface melting in May typically extends inland by 100 to 150 kilometers (60 to 90 miles) along the southern ice sheet perimeter, and along the northwestern Greenland coast (Mellville Coast) for 20 to 30 kilometers (14 to 20 miles) inland.

An examination of the ice sheet masking used for the Greenland Today daily melt and cumulative melt determination has revealed some areas of northern Peary Land and Kronprince Christian Land that are treated as ice sheet when in fact they are seasonal snow and patchy ice areas less than 25 kilometers across (the size of our measurement grid and sensor data samplings). These areas are indicating ice sheet surface melting incorrectly. The data set has been uniformly processed with the current (inaccurate) mask, and so comparisons such as our anomaly plots and cumulative melt extent are generally consistent. Extents and anomalies outside of these two northern peninsula areas are accurate. A new mask and full reprocessing are scheduled for late in 2015.

Conditions in context

Figure 2. The plot at top shows Greenland air temperature anomalies at the 700 millibar level (about 10,000 feet altitude) in degrees Celsius for May 2015. Blues and purples indicate lower than average temperatures. The plot at bottom shows average global monthly air temperature anomaly for November to April 2015, relative to a baseline period of 1951 to 1980, the reference period used by the NASA Goddard Institute of Space Sciences (NASA GISS).||Credit: NASA GISS|  High-resolution image

Figure 2. The plot at top shows Greenland air temperature anomalies at the 700 millibar level (about 10,000 feet altitude) in degrees Celsius for May 2015. Blues and purples indicate lower than average temperatures. The plot at bottom shows average global monthly air temperature anomaly for November to April 2015, relative to a baseline period of 1951 to 1980, the reference period used by the NASA Goddard Institute of Space Sciences (NASA GISS).

Credit: NASA GISS
High-resolution image

Figure 3. The plot shows snowfall anomaly for Greenland (in millimeters of water equivalent) for the winter season of 2014 to 2015. The majority of the eastern coast saw considerably more snowfall than the 1981 to 2010 average. Data are from the NCEP-NCARv1 reanalysis forced model (climate model run using measured weather values as forcing).||Credit: Credit: X. Fettweis, University of Liège|  High-resolution image

Figure 3. The plot shows snowfall anomaly for Greenland (in millimeters of water equivalent) for the winter season of 2014 to 2015. The majority of the eastern coast saw considerably more snowfall than the 1981 to 2010 average. Data are from the NCEP-NCARv1 reanalysis forced model (climate model run using measured weather values as forcing).

Credit: Credit: X. Fettweis, University of Liège
High-resolution image

The low early numbers for surface melt extent are consistent with a very cool month of May, with mid-troposphere temperatures 0.5 degrees Celsius (1 degree Fahrenheit) or more below average everywhere on the island, reaching 3 degrees Celsius (5 degrees Fahrenheit) below the 1981 to 2010 average along the western coast. Cooler-than-average conditions were the rule for the entire winter and early spring, particularly for the western and southwestern sections of the ice sheet. Notable is that this region, extending southwestward to the northeast United States and eastern Canada, is one of the few large regions of the globe with significantly below-average temperatures during this period. The warmest 12 months on record for the globe occurred during May 2014 to April 2015.

The major circulation pattern governing climate trends, the NAO (North Atlantic Oscillation), has been predominantly positive (typical index values of +0.5 to +1.5) through the early part of the year. This tends to produce easterly winds and cool conditions for much of Greenland, and this is reflected in higher snow accumulation for the island, with 1 to 4 feet of excess snowfall (equivalent to 10 to 40 centimeters, or 4 to 12 inches, of excess water accumulation in the form of snow) along the eastern coast. On the Melville Coast (northwest) and far southeastern coast, snowfall was below average by about 5 to 20 centimeters water equivalent, or 6 to 24 inches of snow.

A silver lining

albedo anomaly map

Figure 4. The map shows albedo anomaly for May 2015, relative to the average for May for the 2000 to 2009 period. Red areas near the coast indicate regions where snow has persisted due to cool conditions. In the interior, the general reduction in albedo of Greenland snow observed for the past several years is evident. This is thought to be due to increased soot and dust in Arctic snow cover. However, the trend towards greater decrease in albedo in the northern half, and northwestern areas of Greenland are due in part to sensor degradation in the MODIS sensors over time. Data are from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS), MOD10A1 collection 5.

Credit: J. Box, Geological Survey of Denmark and Greenland (GEUS)
High-resolution image

Albedo (or surface brightness, reflectivity) for the ice sheet has been decreasing significantly for several years, due to the effects of snow grain coarsening due to warmer conditions and possibly from soot from both fires and industrial sources. We have discussed this in earlier posts. However, for May 2015, the cold conditions, late onset of melting and heavy snowfall in the east have created conditions where albedo is higher around much of the perimeter of the ice sheet than has been typical of this century so far. While interior albedo levels are 1 to 4% below the 2000 to 2009 average, a band of the western ice sheet, and much of the eastern near-coastal areas are 3 to 6% brighter than normal. Along the eastern side, much of the brightening is likely due to snow remaining on land and on darker bare ice longer into the spring season than has been typical. A pattern of darkening in the far northwestern areas of the island is in part due to a declining sensitivity of some MODIS channels that is hoped to be corrected in the forthcoming, updated albedo product using MODIS Collection 6 data.

Water-soaked      

firm aquifers map

Figure 5. The map at top shows areas of suspected firn aquifer on the Greenland Ice Sheet, based on analysis of airborne radar data from NASA Operation IceBridge. Thin lines indicate the overall flight lines for the 2011, 2012, and 2013 field programs, and colored areas indicate regions where radar data suggest a buried water layer in the firn. The plot at bottom is an example of a radar profile of the upper part of the ice sheet showing a water layer that has been confirmed by drilling into the ice. Variations in the depth of the aquifer are due to variations in the local amount of melting and to surface topography.

Credit: Clément Miège
High-resolution image

In a melt year that is starting more slowly than average and with more snow accumulation, especially in the east of Greenland, scientists are particularly interested in how and when the meltwater will reach the ocean. It is well known that surface melt extent over the Greenland Ice Sheet is expanding, and as a result the ice sheet is losing mass and contributing to sea level rise. When the surface snow or ice melts, it flows into a complex surface and sub-surface hydrologic system that transports the water from the ice sheet to the ocean. The routing of the water, however, is not simple. The Greenland hydrologic system consists of many features common to hydrologic systems on land, such as streams and lakes visible on the surface of the ice sheet, as well as features unique to the ice sheet, such as moulins and subglacial lakes.

A 2011 discovery in southeastern Greenland has added a new component to the Greenland Ice Sheet hydrologic system: a large firn aquifer. A firn aquifer is similar to an aquifer on land where water is stored in a porous stone or earthen layer, such as sandstone or gravel, in the space between the mineral grains. A firn aquifer is a similar kind of storage in coarse porous snow, called firn. Firn is snow that has persisted through a summer melt season. A firn aquifer resembles the cold, slushy drinks sold in stores during summer. Firn aquifers are formed in areas of both strong summer melting and heavy winter snowfall. Meltwater in the summer soaks down into the snow beneath it, warming the snow to the melting point. Heavy winter snows act like a thick blanket, keeping the layer at the freezing point throughout the winter and into the next summer period, when new melting and warmth recharges the soaked layer. Just like an aquifer on land, it is possible to drill into the firn aquifer and pump water out onto the frozen surface.

Why are firn aquifers important? The behavior of the aquifer will determine how much melt water from Greenland reaches the ocean and how quickly, and may have an effect on ice flow speeds. It is currently estimated that the southeastern Greenland firn aquifer stores 140 billion tons of water, equal to approximately 0.4 millimeter (0.016 inches) of sea level rise. The aquifer may be a temporary feature, delaying delivery of meltwater to the ocean until a sudden outflow, or it may be in equilibrium where meltwater recharges the aquifer each summer by the same amount that leaks each year. Another potential effect is that leaking meltwater from the aquifer can reach the base of the ice sheet, and act to partially lift glaciers off the bedrock. This process is well-known in areas where surface lakes and melt streams occur. Each year brings new data and new discoveries for the firn aquifer.

Further reading

Meltfactor: The ice and climate blog of Dr. Jason Box

Jason Box Web site

Xavier Fettweis Web site

Enormous Aquifer Discovered Under Greenland Ice Sheet

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.

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.