Greenland surface melting in 2021

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Two near-record melt events occurred in the 2021 melt season for the Greenland Ice Sheet, in late July and in mid-August. During the second event, an unprecedented occurrence of rain at the National Science Foundation’s Summit Station took place, the first to be observed in the satellite era. Overall the melt season was unexceptional, owing to a modest start; however, the mid-August heat wave was both strikingly intense and late in the season by several weeks compared to similar events in the record.

Overview of conditions

Figure 1. Top left, cumulative melt days map of Greenland for the 2021 melt season. Top right, map of the difference in number of melt days for 2021 from the 1981-2010 average melt days for the same period. Bottom, daily melt area for Greenland from April 1st through October 31st, 2021 (blue line) 2020 (green line) and 2019 (orange line). In gray are the mean daily melt area for 1981-2010, the inter-quartile range, and the inter-decile range. Credit: National Snow and Ice Data Center/T. Mote, University of Georgia

Figure 1a. The top left map shows cumulative melt days for the Greenland Ice Sheet during the 2021 melt season. The top right map shows the difference in number of 2021 melt days from the 1981 to 2010 average melt days for the same period. The bottom graph shows the daily melt area for the Greenland Ice Sheet from April 1 through October 31, with 2021 shown in blue, 2020 in green line, and 2019 in orange. The grey areas show the average daily melt area for 1981 to 2010, the inter-quartile range, and the inter-decile range.


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

Figure 1b. The top plot shows air temperature as a difference from average, relative to 1981 to 2010, for the period of June 1 through August 31, 2021, in degrees Celsius. The bottom plot shows height difference from average in meters for the 700 millibar pressure level in the atmosphere for the same period. ||Credit: National Snow and Ice Data Center|High-resolution image

Figure 1b. The top plot shows air temperature as a difference from average, relative to 1981 to 2010, for the period of June 1 through August 31, 2021, in degrees Celsius. The bottom plot shows height difference from average in meters for the 700 millibar pressure level in the atmosphere for the same period.

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

1c. The top three maps show cumulative melt days from left to right from 1981, 2001, and 2021. The bottom graph shows bars for cumulative melt days from 1992 to 2021. Credit: National Snow and Ice Data Center, University of Colorado Boulder, T. Mote, University of Georgia|High-resolution image

Figure 1c. The top three maps show cumulative melt days from left to right from 1981, 2001, and 2021. The bottom graph shows bars for cumulative melt days from 1992 to 2021. Credit: National Snow and Ice Data Center, University of Colorado Boulder, T. Mote, University of Georgia
High-resolution image

Figure 1d. This graph shows air temperatures for the summer months of June, July, and August at Summit, Greenland, for 2008-2020 (all years, shown as grey lines) and the three recent years with above-freezing conditions, 2012, 2019, and 2021. Note, the logarithmic scale exaggerates near-freezing temperatures greater than -5 degrees Celsius (23 degrees Fahrenheit). ||Credit: C. Shuman and M. Schnaubelt, University of Maryland, Baltimore |High-resolution image

Figure 1d. This graph shows air temperatures for the summer months of June, July, and August at Summit, Greenland, for 2008-2020 (all years, shown as grey lines) and the three recent years with above-freezing conditions, 2012, 2019, and 2021. Note, the logarithmic scale exaggerates near-freezing temperatures greater than -5 degrees Celsius (23 degrees Fahrenheit).

Credit: C. Shuman and M. Schnaubelt, University of Maryland, Baltimore

High-resolution image

Surface melting of the Greenland Ice Sheet in 2021 was above the 1981 to 2010 average, and extended far higher in elevation than is typical even in recent years (Figure 1a). However this was largely a result of two short-lived heat waves in late July and mid-August, and total cumulative melt-day area is actually near the average for the past 20 years. There were very few melt events following the extreme event of August 14, with surface melting essentially ending by September 10, unlike some recent years. The number of days with melting was slightly higher than average throughout much of southern and western Greenland and slightly below average in the northeastern area. Small areas of the Scoresby Sund (Kangertittivaq) region had up to 30 days more melting than the average.

Averaged over the island, the past summer was approximately 1 degree Celsius (2 degrees Fahrenheit) warmer than average relative to the 1981 to 2010. Temperatures up to 2 degrees Celsius (4 degrees Fahrenheit) above average prevailed over the eastern coast. The west-central area was not as warm with temperatures only 0.6 degrees Celsius (1 degree Fahrenheit) above average. Higher than average air pressure to the east of Greenland, and lower air pressure to the west, resulted in a more southwest-to-northeasterly flow of air than average (Figure 1b).

Surface melt mapping over four decades of satellite data shows that melting has greatly expanded over the ice sheet, including much more of its northern reaches and far more intense melting along the western coast. While the cumulative total melt area has not changed much in the past 20 years, the level of melting is generally higher and more variable than in the 1990s (Figure 1c).

The air temperature record from Summit, Greenland, for the three warmest summers relative to the range for the entire continuous weather observations (2008 to 2020) shows the increased prevalence of daily record high temperatures in the three years, surpassing 0 degrees Celsius (32 degrees Fahrenheit) four times. Satellite data recorded only one other earlier melt event near the Summit, which took place in 1995. The data from 2021 also shows the unusual nature of the warm event of mid-August, usually a period of rapid cooling on the ice sheet (Figure 1d).

More on the rain event at Summit Station

Figure 2. These three photographs were taken from Summit, Greenland, on August 14, 2021. The rain on snow event caused liquid water raindrops on the surfaces of the structures, and the formation of an ice layer from refrozen rain on snow. || Credit: Alicia Bradley and Zoe Courville|High-resolution image

Figure 2. These three photographs were taken from Summit, Greenland, on August 14, 2021. The rain on snow event caused liquid water raindrops on the surfaces of the structures, and the formation of an ice layer.

Credit: Alicia Bradley and Zoe Courville
High-resolution image

The rain event at Summit on August 14, 2021, was the first occurrence since continuous field observations began at that station in 2008. The rain event prompted a search within the available historical literature for reports of rain high on the Greenland Ice Sheet. As noted in our August report, prior to 1995, when a significant melt event occurred, we infer that both melting and rain were absent at Summit for at least the twentieth century because of an absence of ice layers in the ice cores drilled at the site. The most useful report for early weather observations is Hogue (1964), who provides a comprehensive assessment of available weather records for the early to mid-twentieth century. On rain events over the ice cap, Hogue states:

most precipitation falls as snow, but occasionally rain occurs during the warmer months on the outer margin of the icecap….   Heavy rainfall seldom occurs above 6,000 feet [elevation]. However, Belknap reported a heavy rain at Watkins (a temporary camp) at an elevation of 8,840 feet, in July 1933….  At Dye2 on the west slope [of the ice sheet] near the Arctic Circle at an elevation of 7,650 feet, rain of moderate intensity fell on 1 November 1963….  In the Central Station – Eismitte area, rain and drizzle were each reported once on 20 June and 21 June, 1950, respectively, during a three-year period.

Eismitte is at 3,010 meters (9,875 feet) elevation. For comparison, Summit Station is at 3,216 meters (10,551 feet) elevation, and is 155 kilometers (96 miles) away. No later report of rain at elevations above 2,700 meters (8,800 feet) has been found in the available records. Additional information on climate for the Summit area is found in the references listed at the end of this report.

References

Belknap, 1935: Polar Record , Volume 2 , Issue 9 , January 1935, 32 – 35, doi:10.1017/S0032247400033362.

Bilello and Bates, Jan 1975 Summer climate at selected sites on the Ross Ice Shelf and the Greenland Ice Sheet, CRREL Report SR-216, 22p.

Hogue, D.W., 1964. Environment of the Greenland Ice Cap. U.S. Army Natick Laboratories, Natick, Massachusetts Tech. Rept. ES-14:

Ratziki Elizabeth Contribution to the climatology of Greenland. Expeditions polaires francais. Missions Paul Emile Victor Publications E.P. F. 2112 47 Marechal Fayolle Paris 1960.

 Acknowledgements

Greenland Ice Sheet Today is produced at the National Snow and Ice Data Center by Ted Scambos, Julienne Stroeve, and Lora Koenig with support from NASA. NSIDC thanks Jason Box and Robert Fausto of the Geological Survey of Denmark and Greenland (GEUS), Xavier Fettweis, Christopher Shuman, and Thomas Mote for data and collaboration.

 

Data for daily melt ends for one pole, begins for another

Daily melt extent mapping for the Antarctic Ice Sheet will be restarting soon, while mapping for the Greenland Ice Sheet is suspended for the winter. Calibration of yearly melt detection requires analysis of the springtime snow conditions by a separate program. See our March 18, 2013 post for more discussion of melt calibration. A full analysis for the 2021 melt season on the Greenland Ice Sheet will be coming soon.

Our interactive chart supports a retrospective look at past Greenland melt seasons. This will remain available for our users.

Daily image updates will resume for the Greenland Ice Sheet in April 2022.

Rain at the summit of Greenland

On August 14, 2021, rain was observed at the highest point on the Greenland Ice Sheet for several hours, and air temperatures remained above freezing for about nine hours. This was the third time in less than a decade, and the latest date in the year on record, that the National Science Foundation’s Summit Station had above-freezing temperatures and wet snow. There is no previous report of rainfall at this location (72.58°N 38.46°W), which reaches 3,216 meters (10,551 feet) in elevation. Earlier melt events in the instrumental record occurred in 1995, 2012, and 2019; prior to those events, melting is inferred from ice cores to have been absent since an event in the late 1800s. The cause of the melting event that took place from August 14 to 16, 2021, was similar to the events that occurred this late July, where a strong low pressure center over Baffin Island and high air pressure southeast of Greenland conspired to push warm air and moisture rapidly from the south.

Overview of conditions

Figure 1a. The top maps show daily melt extent for the Greenland Ice Sheet for August 14, 15, and 16, 2021. The lower left map shows cumulative melt days for 2021 through Aug 16. The lower right graph shows daily melt extent during mid-summer for all years in the satellite record with a maximum melt extent greater than 800,000 square kilometers (309,000 square miles). The graph areas depict the daily melt area for the 1981 to 2010 average, the interquartile range, and the interdecile range. All melt events observed by the NSIDC satellite record are circled in cyan; the rain (red circle) and melt event of 2021 is the only event of this type in the 43-year record. About the data ||Credit: National Snow and Ice Data Center/T. Mote, University of Georgia|High-resolution image

Figure 1a. The top maps show daily melt extent for the Greenland Ice Sheet for August 14, 15, and 16, 2021. The lower left map shows cumulative melt days for 2021 through Aug 16. The lower right graph shows daily melt extent during mid-summer for all years in the satellite record with a maximum melt extent greater than 800,000 square kilometers (309,000 square miles). The graph areas depict the daily melt area for the 1981 to 2010 average, the interquartile range, and the interdecile range. All melt events observed by the NSIDC satellite record are circled in cyan; the rain (red circle) and melt event of 2021 is the only event of this type in the 43-year record. 

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

Figure 1b. The top graph shows 2-meter air temperature and dew point for Summit Station, Greenland, on August 14 and 15. The bottom graph shows air pressure at Summit during the melt event. Credit: National Oceanic and Atmospheric Administration (NOAA) and Christopher Shuman, NASA Joint Center for Earth Systems Technology and NASA Goddard Space Flight Center|High-resolution image

Figure 1b. The top graph shows 2-meter air temperature and dew point for Summit Station, Greenland, on August 14 and 15. The bottom graph shows air pressure at Summit during the melt event.

Credit: National Oceanic and Atmospheric Administration (NOAA) and Christopher Shuman, University of Maryland, Baltimore, Joint Center for Earth Systems Technology at NASA Goddard Space Flight Center
High-resolution image

Widespread surface melting and an extensive rainfall event along the southeast coast extending up to the Summit region of Greenland occurred on August 14 and 15, with melt area returning to moderate levels on August 16 (Figure 1a). Melt extent peaked at 872,000 square kilometers (337,000 square miles)on August 14, dropping to 754,000 square kilometers on the 15 and 512,000 square kilometers (198,000 square miles) on August 16. Only 2012 and 2021 have had more than one melt event of 800,000 square kilometers (309,000 square miles) in extent, and the August 14 event was the latest date for this scale of melt extent in the satellite record.

Temperatures surpassed the freezing point at Summit Station around 0700 UTC (5:00 am local time) on August 14, and the rain event began at the same time (Figure 1b). For the next several hours, rain fell and water droplets were seen on surfaces near the camp as reported by on-station observers. At about 1400 UTC the snow surface began to form thin sheets of ice crystals as the rain froze into the snow. Winds were 9.8 meters per second (22 miles per hour) from the southwest with a mix of freezing and non-freezing rain. Temperatures peaked at 0.48 degrees Celsius (33 degrees Fahrenheit) around 10:40 UTC and dropped below freezing around 16:20 UTC. Temperatures fell steadily through the evening. As skies cleared late in the evening, a sharp cooling brought temperatures to -8.5 degrees Celsius (16.7 degrees Fahrenheit) early on August 15 (Figure 2). Temperatures at Summit did not reach the melting point on August 15 or 16.

The total aerial extent of surface melting (total melt-day extent) for 2021 through August 16 is 21.3 million square kilometers (8.2 million square miles), tied for the fourteenth highest total to date, and well above the 1981 to 2010 average of 18.6 million square kilometers (7.2 million square miles).

Conditions in context

Figure 2a. The top plot shows 2-meter air temperature for August 14, as a departure from the 1979-2000 reference period for the Arctic and surrounding regions. The plot indicates the warm conditions in southwestern Greenland extending to the Summit region. The bottom plot shows average sea level pressure for the same day. Air circulation between the low pressure center over Baffin Island and the high pressure center off the southern tip of Greenland drove air and moisture rapidly northward. The white star marks the location of Summit Station in both maps. ||Credit: ClimateReanalyzer.org, Climate Change Institute, University of Maine |High-resolution image

Figure 2a. The top plot shows 2-meter air temperature for August 14, as a departure from the 1979 to 2000 reference period for the Arctic and surrounding regions. The plot indicates the warm conditions in southwestern Greenland extending to the Summit region. The bottom plot shows average sea level pressure for the same day. Air circulation between the low pressure center over Baffin Island and the high pressure center off the southern tip of Greenland drove air and moisture rapidly northward. The white star marks the location of Summit Station in both maps.

Credit: ClimateReanalyzer.org, Climate Change Institute, University of Maine
High-resolution image

Figure 2b. The top graph shows estimated daily surface runoff and the bottom graph shows daily total melt water (no rain) for several recent warm-summer years for the Greenland Ice Sheet. The grey band and dark line show the average daily values for the 1981 to 2010 reference period; the blue dotted line shows the maximum runoff or melt mass within the 1981 to 2010 record. The data are from a regional climate model run using ERA-5 reanalysis as forcing, and forecast data for the period shown following Aug 14. ||Credit: MARv3.12, X. Fettweis, University of Liége/CLIMATO |High-resolution image

Figure 2b. The top graph shows estimated daily surface runoff and the bottom graph shows daily total melt water (no rain) for several recent warm-summer years for the Greenland Ice Sheet. The grey band and dark line show the average daily values for the 1981 to 2010 reference period; the blue dotted line shows the maximum runoff or melt mass within the 1981 to 2010 record. The data are from a regional climate model run using ERA-5 reanalysis as forcing, and forecast data for the period shown following Aug 14.

Credit: MARv3.12, X. Fettweis, University of Liége/Greenland-CLIMATO
High-resolution image

An air circulation pattern very similar to the extensive melt events of late July (see previous post) caused the extensive melt and rain event of mid-August 2021. A moderately strong low pressure center (center pressure 987 millibars) moved northeastward across Hudson Bay towards Baffin Island (Figure 2a). At the same time, high air pressure off the southern end of Greenland in the Denmark Strait created a strong pressure gradient in the southern Labrador Sea and Baffin Bay, forcing a strong wind event from the south-southwest to the northeast and onto the southwestern Greenland coast. This warm moist air then covered the island over the next few days. As clearing skies emerged on August 15, much of the north-central ice sheet cooled significantly.

Warm conditions and the late-season timing of the three-day melt event coupled with the rainfall led to both high melting and high runoff volumes to the ocean. Data from MARv3.12 suggests this was the largest rainfall event since 1950, the beginning of ERA-5 (Figure 2b). Melt volume does not, however, include the additional water from rainfall during the warm air intrusion, although rainfall in runoff areas (where the surface is icy and impermeable) is included. Over most of the ice sheet, meltwater (or rainfall in the upper reaches of the ice sheet) percolates into remaining snow and refreezes; however, in bare ice and water-saturated snow areas near the coast, meltwater (and rainfall) runoff occurs resulting in the ice sheet losing mass. On August 15 2021, the surface mass lost was seven times above the mid-August average according to MARv3.12. At this point in the season, large areas of bare ice exist along much of the southwestern and northern coastal areas, with no ability to absorb the melt or rainfall. Therefore, the accumulated water on the surface flows downhill and eventually into the ocean.

Rain check

Figure 3. The top panel shows air temperature in degrees Celsius from an automated weather station at South Dome, Greenland, for August 13, 14, and 15, showing the more extensive time above the freezing point for the southern area of the upper Greenland Ice Sheet. The bottom graph shows accumulated rainfall in millimeters at Crawford Point Weather Station, located above the area of meltwater ponds and runoff on the western ice sheet. Credit: Geological Survey of Denmark and Greenland (GEUS) Greenland Climate Net (GC-Net)|High-resolution image

Figure 3. The top panel shows air temperature in degrees Celsius from an automated weather station at South Dome, Greenland, for August 13, 14, and 15, showing the more extensive time above the freezing point for the southern area of the upper Greenland Ice Sheet. The bottom graph shows accumulated rainfall in millimeters at Crawford Point Weather Station, located above the area of meltwater ponds and runoff on the western ice sheet.

Credit: Geological Survey of Denmark and Greenland (GEUS) Greenland Climate Net (GC-Net)
High-resolution image

Above freezing temperatures and rainfall were widespread to the south and west of Greenland during the three-day period, with exceptional readings from several remote weather stations in the area. Total rainfall on the ice sheet was 7 billion tons. At South Dome, the highest point on the southern lobe of the ice sheet at 2,850 meters (9,350 feet) elevation melt was recorded by satellite during all three days of the warm event, and the early part of this period (Figure 3) shows the rapid warming and persistent above-freezing conditions for August 14 and 15.

References

Fettweis, X., M. Tedesco, M. Broeke, J. and Ettema. 2011. Melting trends over the Greenland ice sheet (1958–2009) from spaceborne microwave data and regional climate models. The Cryosphere, 5(2), 359-375, doi:10.5194/tc-5-359-2011.

Nghiem, S. V., D. K. Hall, T. L. Mote, M. Tedesco, M. R.  Albert, K. Keegan, C. A. Shuman, N. E. DiGirolamo, and G. Neumann. 2012. The extreme melt across the Greenland ice sheet in 2012. Geophysical Research Letters, 39(20), doi:10.1029/2012GL053611.

The Geological Survey of Denmark and Greenland (GEUS) is carrying forward the Greenland Climate Network (GC-Net) initiated by Konrad Steffen of the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder in 1995.

Summit Station is owned and operated by the National Science Foundation Office of Polar Programs with permission from the Government of Greenland.

Acknowledgements

A special acknowledgement goes out to Alicia Bradley and Zoe Courville for reporting observations at Summit Station, Greenland.

Greenland Ice Sheet Today is produced at the National Snow and Ice Data Center by Ted Scambos, Julienne Stroeve, and Lora Koenig with support from NASA. NSIDC thanks Jason Box and Robert Fausto of the Geological Survey of Denmark and Greenland (GEUS), Xavier Fettweis, Christopher Shuman, and Thomas Mote for data and collaboration.

Large melt events change the story of 2021

The Greenland Ice Sheet had two extensive melt events in the second half of July. The second melt event had the seventh-largest melt area and fourth-highest runoff in the satellite record, which began in 1978. However, snow cover from earlier snowfall in early summer blunted the potential impact of the melting by limiting the exposure of bare ice and reducing runoff. The two events resulted in the 2021 season flipping from a net gain of ice to near-average net change; however, more melting is forecast.

Overview of conditions

Figure 1. The top left map of the Greenland Ice Sheet illustrates the total number of melt days through August 5, 2021. The top right map shows the difference between total 2021 melt days from January 1 to August 5 and the number of 1981 to 2010 average melt days for the same period. The lower graph shows daily area in square kilometers of surface melting from June 1 to August 15, 2021, for the four years with the six largest melt events (by area) in the satellite monitoring record. In gray are the average daily melt area for 1981 to 2010, the inter-quartile range, and the interdecile range. ||Credit: National Snow and Ice Data Center /T. Mote, University of Georgia | High-resolution image

Figure 1. The top left map of the Greenland Ice Sheet illustrates the total number of melt days through August 5, 2021. The top right map shows the difference between total 2021 melt days from January 1 to August 5 and the number of 1981 to 2010 average melt days for the same period. The lower graph shows daily area in square kilometers of surface melting from June 1 to August 15, 2021, for the four years with the six largest melt events (by area) in the satellite monitoring record. In gray are the average daily melt area for 1981 to 2010, the inter-quartile range, and the interdecile range.

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

The total aerial extent of surface melting (total melt-day extent) through August 5 is just under 17.8 million square kilometers (6.87 million square miles), slightly above the 1981 to 2010 average of 15.2 million square kilometers (5.87 million square miles). Melting remains slightly below average along the west-central area of the ice sheet but is now well above average in the east-central region near Scoresby Sund. Much of the high-elevation interior of the ice sheet is three to five days above the average number of melt days as a result of the two extensive melt events in July, peaking on July 19 and 28. However, melt days in low-elevation areas in the north and northwest, as well as the west-central part of the ice sheet, remain below average. These are the regions where bare ice is exposed and where melt runs off into the ocean. As a result, the 2021 net runoff is below average as of this post.

Conditions in context

Figure 2a. The top plot shows air temperature as a difference from average, relative to 1981 to 2010, for the period of May 1 through June 20, 2021, in degrees Celsius. The bottom plot shows height difference from average in meters for the 700 millibar pressure level in the atmosphere for the same period. ||Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research| High-resolution image

Figure 2a. The top plot shows air temperature as a difference from average, relative to 1981 to 2010, for the period of June 1 through August 5, 2021, in degrees Celsius. The bottom plot shows height difference from average in meters for the 700 millibar pressure level in the atmosphere for the same period.

Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research
High-resolution image

Figure 2b. This graph shows the estimates of surface mass balance (SMB) for the Greenland Ice Sheet for the 2020 autumn to 2021 winter and spring season (red line) through August 4, 2021 (based on forecast and re-analysis), relative to the 1981 to 2010 average. It also includes several recent years for comparison. SMB is the sum of snowfall and rainfall, minus any evaporation or runoff. The bottom graph shows SMB difference from average across the ice sheet through August 4. The estimates come from the MARv3.11 model based on daily weather measurements and projections. ||Credit: Amory et al. 2021, MARv3.11, Xavier Fettweis, Université de Liège, Belgium | High-resolution image

Figure 2b. This graph shows the estimates of surface mass balance (SMB) for the Greenland Ice Sheet for the 2020 autumn to 2021 winter and spring season (red line) through August 4, 2021 (based on forecast and re-analysis), relative to the 1981 to 2010 average. It also includes several recent years for comparison. SMB is the sum of snowfall and rainfall, minus any evaporation or runoff. The bottom graph shows SMB difference from average across the ice sheet through August 4. The estimates come from a regional climate model forced by the ECMWF Reanalysis 5th Generation (ERA5) reanalysis data and forecast based on daily weather measurements and projections.

Credit: Amory et al. 2021, MARv3.12, Xavier Fettweis, Université de Liège, Belgium
High-resolution image

Weather conditions through mid-summer can be summarized by looking at the average air temperature and air pressure at the 700 millibar level in the atmosphere at about 10,000 feet (Figure 2a). Air temperatures above Greenland from June through early August were slightly higher than average across the entire ice sheet, ranging from 0.2 degrees Celsius to 1 degree Celsius (0.4 degrees to 1.8 degrees Fahrenheit), with the warmest conditions in the far north, east-central coast, and southern tip of the island. Air pressure patterns, indicated by the height of the 700 millibar level (generally about 10,000 feet above the surface, but higher under high pressure conditions, and lower under low pressure conditions), are dominated by an area of low pressure over Baffin Island and the Canadian Arctic archipelago. This low pressure drove warm air across the southern tip of Greenland and up along the southeastern coast.

Note, we use the 700 millibar level for both air temperature and air pressure evaluation because of the effect of the large, high-elevation ice sheet. Sea-level or near-sea-level values for air temperature and pressure must be converted from the values at the ice sheet surface across the island to equivalent sea level values, often resulting in misleading patterns not actually observed at the level of the ice sheet surface.

The trends for this year and several recent years in net surface increase or decrease in ice and snow, or surface mass balance (SMB), are shown at the top of Figure 2b. This illustrates the large impact the intense melt events of late July have had, moving the net change in the ice sheet from an increase of 50 billion tons relative to the average to a near-zero change by the end of July. Although we are nearing the end of the melt season, further warm events, as forecasted by the Regional Atmosphere Model Global Forecast System (MAR-GFS) for mid-August, may push the trend further downward. Temperatures could reach more than 15 degrees Celsius (27 degrees Fahrenheit) above average on August 15.

Two heat waves

Figure 3. The top graph shows the Greenland ice sheet melt extents (in pink) for July 19 (left) and July 28, 2021, with high temperatures for several Programme for Monitoring of the Greenland Ice Sheet (PROMICE) weather stations shown. The bottom graph shows average air pressure shown as height above sea level for the 700 millibar pressure level for July 27 to 29, 2021. ||Credit: National Snow and Ice Data Center | High-resolution image

Figure 3. The top graph shows the extent of the Greenland Ice Sheet melt (in pink) for July 19 and July 28, 2021, with high temperatures at several weather stations from the Programme for Monitoring of the Greenland Ice Sheet (PROMICE). The bottom graph shows average air pressure shown as height above sea level for the 700 millibar pressure level for July 27 to 29, 2021.

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

The peak melt extents for the 2021 Greenland melt season occurred on July 19 and July 28. On the July 19 about 700,000 square kilometers (270,000 square miles) or 40 percent of the ice sheet experienced melt. On July 28, about 880,000 square kilometers (340,000 square miles) or 54 percent of the surface melted. Temperatures measured at several weather stations from the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) recorded above-freezing temperatures along the entire coastal ice edge region on both peak days, with the exception of the high-elevation East Greenland Ice-core Project station, which showed temperatures in the -2 to -3 degrees Celsius (28 to 27 degrees Fahrenheit) range at mid-day, approximately 10 degrees Celsius (18 degrees Fahrenheit) above average. At summit, the highest point on the ice sheet at 3,216 meters (10,551 feet) above sea level, air temperatures reached -1.6 degree Celsius (29 degrees Fahrenheit) on July 19 and -0.7 degrees Celsius (30.7 degrees Fahrenheit) on July 28. The summit area had no surface melting. These numbers are preliminary and were provided by the National Oceanic and Atmospheric Administration Global Monitoring Laboratory.

An atmospheric river of warm air drove the second melt area peak on July 28. Weather conditions were guided by the strong pressure gradient between a high-pressure area that moved northwestward from the Denmark Strait (between Greenland and Iceland) and a persistent low-pressure area over the Canadian Arctic archipelago. The event started with snow and rain in the northwest coast, but associated warm conditions caused extensive melting over much of western and northern Greenland in the succeeding days.

Over most of the ice sheet, meltwater percolates into remaining snow and refreezes; however, in bare ice and water-saturated snow areas near the coast, meltwater runoff occurs. While the overall amount of runoff has been reduced by repeated snowfall events through June and July, the July 28 event (-12.5 billion tons) was the third-highest daily ablation (negative SMB) rate, after July 11, 2012 (-12.9 billion tons) and July 31, 2019 (-16.1 billion tons).

Between late-season snows

Figure 4. This map shows albedo, or reflectivity, derived from the European Space Agency (ESA) Sentinel-3 satellite Ocean and Land Colour Instrument (OLCI) for the Greenland ice sheet for the past five years. Note the relatively high trend for 2021 prior to the recent melt events. The bottom map shows the surface reflectivity at a weather station along the west-central coast of Greenland, showing how repeated snow events brighten the surface. A snow-covered surface reduces runoff by absorbing some of the meltwater and reflecting solar energy back to space. The latest event shown is between the two melt periods. ||Credit: Polar Portal| High-resolution image

Figure 4. This map shows albedo, a measure of reflectivity, derived from the European Space Agency (ESA) Sentinel-3 satellite Ocean and Land Colour Instrument (OLCI) for the Greenland Ice Sheet for the past five years. Note the relatively high trend for 2021 prior to the recent melt events. The bottom map shows the surface reflectivity at a weather station along the west-central coast of Greenland, showing how repeated snow events brighten the surface. A snow-covered surface reduces runoff by absorbing some of the meltwater and reflecting solar energy back to space. The latest event shown is between the two melt periods.

Credit: Jason Box, The Geological Survey of Denmark and Greenland (GEUS) and Polar Portal
High-resolution image

The Ocean and Land Color Instrument on the European Space Agency (ESA) Sentinel-3 satellite tracks Greenland’s snow and ice albedo, or net reflectivity, on a daily basis since 2017 at a spatial resolution of 300 meters (about 1000 feet). Trends for the Greenland Ice Sheet in summer are shown for the past five years in Figure 4, and indicate that overall, the ice sheet is far brighter this year than the previous four years in the month of July. However, overall reflectivity dropped sharply as the two melt events removed large areas of thin snow cover and exposed more bare ice. This set the stage for the meltwater runoff on July 28, despite low runoff amounts earlier in the month. The impact of small snow events on reflectivity, and therefore the amount of energy the ice sheet surface absorbs, can be seen in the lower part of Figure 4.

Greenland in the greenhouse

Figure 5. This plot shows the amount of human-caused carbon dioxide (CO2) emissions versus the daily maximum snowmelt extent for each year in the satellite monitoring period from 1979 to 2021. Symbol colors change with each decade (1979 is included in the 1980s blue color). Several years of high and low melt extents are identified. The point for 2021 assumes that July 28 will be the maximum daily melt extent for 2021. ||Credit: J. Stroeve and National Snow and Ice Data Center | High-resolution image

Figure 5. This plot shows the amount of human-caused carbon dioxide (CO2) emissions versus the daily maximum snowmelt extent for each year in the satellite monitoring period from 1979 to 2021. Symbol colors change with each decade (1979 is included in the 1980s blue color). Several years of high and low melt extents are identified. The point for 2021 assumes that July 28 will be the maximum daily melt extent for 2021.

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

Increased carbon dioxide (CO2) emissions linked to human activity correlate with the general increasing trend of maximum daily melt area in a summer melt season. Figure 5 provides an approximate guide to the impact of greenhouse gas emissions and underscores a similar relationship between minimum sea ice extent and emissions published in 2016.

References

Notz, D. and J. Stroeve. 2016. Observed Arctic sea-ice loss directly follows anthropogenic CO2 emission. Science. doi:10.1126/science.aag2345.

Erratum

On August 18, we changed the following statement from the sixth-largest melt area to seventh-largest melt area: The second melt event had the sixth-largest melt area and fourth-highest runoff in the satellite record, which began in 1978. Figure 1 has also been updated to match the text.

Greenland’s 2021 spring: more snow, less melt

Surface melt and total melt-day area for the Greenland Ice Sheet at the end of the 2021 spring season was below the 1981 to 2010 average. Snowfall and rain (minus runoff) added mass to the ice sheet. As of June 20, total mass gain for the ice sheet since September 2020 was slightly above average. The spike from June 25 to June 27 will be discussed in later a post.

Overview of conditions

Figure 1. The top left map of the Greenland Ice Sheet shows the total number of surface melt days from April 1 through June 20, 2020. The top right map shows the difference between total 2020 melt days and the number of 1981 to 2010 average melt days for the same period. The lower graph shows daily area in square kilometers of surface melting from April 1 to June 20, 2020, with daily melt extent trends for the preceding four years, including 2012, the record year for total melt area. Credit: National Snow and Ice Data Center/T. Mote, University of Georgia | High-resolution image

Figure 1. The top left map of the Greenland Ice Sheet illustrates the total number of melt days through June 20, this year. The top right map shows the difference between total 2021 melt days from January 1 to June 20 and the number of 1981 to 2010 average melt days for the same period. The lower graph shows daily area in square kilometers of surface melting from April 1 to June 20, 2021, with daily melt extent trends for the preceding five years.

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

The total aerial extent of surface melting (total melt-day extent) through June 20 was just over 2.49 million square kilometers (961,000 square miles), 1.5 times below the 1981 to 2010 average of 3.72 million square kilometers (1.44 million square miles). Melting was slightly below average along the west-central ice sheet, and well below average (10 to 12 days behind the average rate) along the southwestern edge of the ice sheet. Limited areas of the north and northwest had slightly above average melting, but the total extent of these areas was low.

Conditions in context

Figure 2. The top plot shows air temperature as a difference from average, relative to 1981 to 2010, for the period of April 1 through June 20, 2020, in degrees Celsius. The bottom plot shows air pressure difference from average, relative to 1981 to 2010. This is shown as the height difference from average of the 700 mb pressure level (about 10,000 feet), in meters. ||Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research | High-resolution image

Figure 2. The top plot shows air temperature as a difference from average, relative to 1981 to 2010, for the period of May 1 through June 20, 2021, in degrees Celsius. The bottom plot shows height difference from average in meters for the 700 millibar pressure level in the atmosphere for the same period.

Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research
High-resolution image

Average air temperature at 700 millibar (about 10,000 feet) and the average height of the 700 millibar level (a measure of air pressure) summarize springtime weather conditions. Air temperatures above Greenland varied across the ice sheet, with warm conditions in the northwest and cool conditions across the southeast. The region near Thule in the northwest was more than 2 degrees Celsius (4 degrees Fahrenheit) above the 1981 to 2010 average, with conditions near the major Helheim Glacier in the southeast were about 2 degrees Celsius (4 degrees Fahrenheit) below average.

Air pressure patterns, indicated by the height above average of the 700 millibar level (about 10,000 feet above ground, but higher under high pressure conditions, and lower when low air pressure is present) show an area of moderate high pressure in the northwest of the island and low pressure over the Irminger Sea between Greenland and Iceland.

Greenland is snowy

Figure 3. This graph shows the surface mass balance (SMB) for the Greenland Ice Sheet for the 2019 autumn to 2020 spring season (red line) through June 20, 2020, relative to the 1981 to 2010 average. ||Credit: X. Fettweis, Université de Liège, Belgium |High-resolution image

Figure 3a. This graph shows the estimates of surface mass balance (SMB) for the Greenland Ice Sheet for the 2020 autumn to 2021 spring season (red line) through June 30, 2021 (based on forecast and re-analysis), relative to the 1981 to 2010 average. It also includes several recent years for comparison. SMB is the sum of snowfall and rainfall, minus any evaporation or runoff. The estimates come from the MARv3.11 model based on daily weather measurements and projections.

Credit: Amory et al. 2021MARv3.11, Xavier Fettweis, Université de Liège, Belgium
High-resolution image

Figure 3b. The top left map shows the total surface mass balance (SMB) over Greenland since September 1, 2020 up to June 20, 2021. The top right map shows the difference from the 1981 to 2010 average, in centimeters of water equivalent. At the bottom is a picture of the west-central area of the Greenland Ice Sheet taken on June 21, 2021, showing persistent snow cover over the fractured ice of the ice sheet. || Credit: Amory et al, 2021| Photo credit: Jason Box, Geological Survey of Denmark and Greenland (GEUS) |High-resolution image

Figure 3b. The top left map shows the total surface mass balance (SMB) over Greenland since September 1, 2020 up to June 20, 2021. The top right map shows the difference from the 1981 to 2010 average, in centimeters of water equivalent. At the bottom is a picture of the west-central area of the Greenland Ice Sheet taken on June 21, 2021, showing persistent snow cover over the fractured ice of the ice sheet.

Credit: Amory et al, 2021

Photo credit: Jason Box, Geological Survey of Denmark and Greenland (GEUS)
High-resolution image

As of June 20, total surface mass balance for the ice sheet was slightly above average total input of snow and rain since September 2020, at about 550 billion tons, 41 billion tons more than average (Figure 3a).

Total snowfall was slightly above average for the ice sheet. Areas that received extra snow this year were across the southeast, where some areas saw 50 to 70 centimeters (20 to 28 inches) more snow water equivalent than average, and to a lesser degree along the western coast (Figure 3b). Large areas of the central and northeastern ice sheet were near-average for the year so far.

Surface mass balance over the ice sheet from September 1, 2020, to June 20, 2021, was about 8 percent above the 1981 to 2010 average, with 7 percent above average snowfall and 10 percent below average melt runoff.

Greenland is bright

Figure 5. The map shows albedo, or reflectivity, for the Greenland Ice Sheet on June 20, 2021, compared to the 2017 to 2020 average.

Figure 4. The map shows albedo, or reflectivity, derived from the European Space Agency (ESA) Sentinel-3 satellite Ocean and Land Colour Instrument (OLCI) for the Greenland Ice Sheet on June 20, 2021, compared to the 2017 to 2020 average. Red areas in the northwest and portion of the northeast indicate darker surfaces compared to the 2017 to 2020 average. The plot on the bottom shows total bare ice exposure for the Greenland Ice Sheet for the past four years and for 2021 through June 20.

Credit: Polar Portal
High-resolution image

Using the European Space Agency (ESA) Sentinel-3 satellite Ocean and Land Colour Instrument (OLCI), Greenland’s snow and ice albedo, or net reflectivity, tracked on a daily basis at a resolution of 300 meters (about 1,000 feet). This product is now available from the Danish Greenland Geological Survey (GEUS). The map for June 20 shows a slightly darker surface over a broad region of the northwestern ice sheet, with narrow areas of much darker surface near the coast where above average melting and runoff has occurred. Most of the central western ice edge and southwest ice edge, where ablation areas or exposed ice occur, was considerably brighter than average (blue areas). This region is usually much wider at this point in the season but is still covered by some snow from the past winter, as shown in the Figure 3b photograph. The extent of bare ice exposure is tracking near the lowest levels for the last five years except 2018, which was an especially snowy and low-melt year.

Further reading

Amory, C., C. Kittel, L. Le Toumelin, C. Agosta, A. Delhasse, V. Favier, X. and Fettweis. 2021. Performance of MAR (v3.11) in simulating the drifting-snow climate and surface mass balance of Adélie Land, East Antarctica, Geoscientific Model Development, 14, 3487–3510, doi:10.5194/gmd-14-3487-2021.

The Antarctic 2020 to 2021 melt season in review

With the exception of the northern and southern Antarctic Peninsula, the Antarctic melt season for 2020 to 2021 was unremarkable and below the 1990 to 2020 average. While the Peninsula melt season began with several strong melt events in early November, both that region and several others had little melt in January, which is usually the peak of the season. In mid-December, strong winds from the north brought warm conditions as far as the South Pole, resulting in a large but brief event in the northern Filchner Ice Shelf.

Overview of conditions

Melt days for Antarctica for 2020 to 2021 year

Figure 1a. The top left map shows the total melt days for the Antarctic Ice Sheet for the 2020 to 2021 melt year. The top right map shows the difference from average relative to the 1990 to 2020 reference period. The bottom graph shows daily melt extent as a percent of the ice cap for the 2020-2021 season through April 1, and the average values and ranges for the reference period.

Credit: M. MacFerrin, CIRES and T. Mote, University of Georgia
High-resolution image

Melt extents for different regions of Antarctica

Figure 1b. These graphs show episodes of significant melt extent in different regions of Antarctica, as depicted in the map on the top left, during the 2020 to 2021 melt year.

Credit: M. MacFerrin, CIRES and T. Mote, University of Georgia
High-resolution image

Since mid-February, melting on the Antarctic continent dropped to almost nil, capping a season that started with a few intense melt events in the Peninsula, the Amery Ice Shelf, and the Filchner Ice Shelf (see map). In the Peninsula, over the northern Larsen C and Larsen B remnant ice shelves, there were 30 days more melt days than during the 1990 to 2020 reference period. The mid-peninsula regions, including the George VI Ice Shelf and the Wilkins Ice Shelf, had near-average to below-average melt seasons. By contrast, the southern area of the Peninsula had an above average number of melt days, notably in the area of Stange Ice Shelf. Elsewhere, it is the absence of melt that is most notable: the Amery Ice Shelf had 5 to 10 days below average melt days; the Roi Baudoin Ice Shelf had about 10 days below average; and in the northeastern Ross Ice Shelf there was essentially zero extensive surface melting recorded. However, in the Filchner Ice Shelf and Brunt ice shelf, a brief but extensive melt event occurred in mid-December that reached far to the south on the ice shelf surface, covering the entire length of the shelf.

Conditions in context

Temperature and Sea Level Pressure over Antarctica Jan through March 2021

Figure 2. The top plot shows the departure from average air temperature in the Antarctic at the 925 hPa level, in degrees Celsius, from January 1 to March 31, 2021. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures. The bottom plot shows the departure from average sea level pressure in millibars for the same time period. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Antarctic climate for the last part of the melt season, from January 1 to March 31, exhibited near-average to cool conditions near the coast, where the majority of surface melting tends to occur. However, conditions were above average near the South Pole and Weddell Sea (Figure 2, top). An atypical and intense Amundsen Sea low-pressure drove strong winds from the east along the coast of the West Antarctic Ice Sheet and kept the eastern Ross Ice Shelf cooler than average (Figure 2, bottom). Warm conditions in eastern Wilkes Land triggered a few significant melt events, and slightly above-average melting.

Warm event on the Filchner Ice Shelf

Weather conditions for Antarctica for mid-December.

Figure 3. These two plots show weather conditions for Antarctica during mid-December 2020. shows the departure from average air temperature in the Antarctic at the 925 hPa level, in degrees Celsius, from December 3 to December 17, 2020, the peak of the melt event. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures. The bottom plot shows the departure from average sea level pressure in millibars from December 10 to December 20, 2020. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

An unusually large area of melting occurred on the Filchner Ice Shelf in mid-December, induced by strong winds from the north (see map). The Filchner Ice Shelf is a relatively narrow ice shelf region on the eastern side of Berkner Island and the large Ronne Ice Shelf. High air pressure in Queen Maud Land and a large low-pressure area stretching across the Ronne Ice Shelf drove the wind pattern, bringing warm conditions all along Coats Land and as far as the South Pole (Figure 3). The South Pole remained well below freezing, but temperatures were still above average during this period. Temperatures from December 13 to December 17 averaged more than 3.5 degrees Celsius (6.3 degrees Fahrenheit) above the 1981 to 2010 reference period for the area. Surface melting was indicated as far south as Support Force Glacier at 83 degrees South. This pattern where low pressure over the eastern Amundsen Sea, Antarctic Peninsula, and western Weddell brings warm winds inland is an example of a climate trend as noted by our colleagues Kyle Clem and Ryan Fogt and others in a 2020 paper.

Further reading

Clem, K. R., R. L. Fogt, J. Turner, B. R. Lintner, G. J. Marshall, J. R. Miller and J. A. Renwick. 2020. Record warming at the South Pole during the past three decades. Nature Climate Change, 10(8), 762-770, doi:10.1038/s41558-020-0815-z.

Antarctica Today: improved processing; low melt so far

The melt mapping tool for Antarctica Today has been improved after a revision was made to the data processing used for Greenland Today. The adjustment accounts for more widespread occurrences of unusual firn structure in Antarctica. Firn is older subsurface snow that can produce false indications of melt under certain conditions. With the correction applied, a first look at the 2020 to 2021 season points to an intense melt season in the northernmost and southernmost Antarctic Peninsula, but generally below-average melting elsewhere on the continent.

Current conditions

Figure 1. The top left map shows the total melt days for the Antarctic Ice Sheet between November 1, 2020 to February 16, 2021. The top right map shows the difference from average relative to the 1989 to 2010 reference period; bottom, daily melt extent as a percent of the ice cap for the 2020-2021 season through 16 February, and the average values and ranges for the reference period. Credit: M. MacFerrin, CIRES and T. Mote, University of Georgia |High-resolution image

Figure 1a. The top left map shows the total melt days for the Antarctic Ice Sheet from November 1, 2020 to February 16, 2021. The top right map shows the difference from average relative to the 1990 to 2020 reference period. The  bottom graph shows daily melt extent as a percent of the ice cap for the 2020-2021 season through February 16, and the average values and ranges for the reference period.

Credit: M. MacFerrin, CIRES and T. Mote, University of Georgia
High-resolution image

Figure 2, top, total melt days for the Peninsula region for 01 November 2020 to 16 February 2021. Note scale change from Figure 1. Bottom, daily total melt as a percent of the total ice area of the region for the 2020-2021 season through 16 February, and the average values and ranges for the reference period (1989-2010).

Figure 1b. The top map of the Antarctic Peninsula shows total melt days from November 1, 2020 to February 16, 2021. The bottom graph shows the daily total melt as a percent of the total ice area of the region for the 2020 to 2021 season through February 16, and the average values and ranges for the 1990 to 2020 reference period.

Credit: M. MacFerrin, CIRES and T. Mote, University of Georgia
High-resolution image

Antarctic surface snow melt extent through February 16, 2021, has been above average in the northernmost and southernmost sections of the Antarctic Peninsula, but below average in nearly all other areas so far this season (Figure 1a). In early December, much of the Filchner Ice Shelf briefly experienced surface melt, a region that rarely has surface melting (Figure 1a, top right). However, much of coastal East Antarctica had significantly below average melting. This late in the melt season the ice surfaces of the Amery and Roi Baudouin Ice Shelves are usually flooded with extensive meltwater in the form of flooded snow, lakes, and even rivers. However, such features are absent this year.

On the Antarctic Peninsula, a strong melt event in the first week of November was limited to the northeastern sector. Strong foehn, or chinook, winds warmed the northern Larsen C and remnant Larsen B Ice Shelves (Figure 1b). This early surge in surface melting did not persist as it had in some record-setting past years like 1992-1993 and 2001-2002. Surface melting resumed in December and January, leading to significant melt ponding on the northern Larsen C Ice Shelf and decade-old land fast sea ice in the Larsen B embayment. Also of note is the very low number of melt days on the Wilkins and George VI Ice Shelves, usually the regions with the highest number of melt days on the continent.

Conditions in context

weather conditions over Antarctica

Figure 2. The top plot shows surface temperatures as a difference from average for the core of Antarctica’s summer melt season, December 15, 2020 to February 15, 2021. The bottom plot shows average surface winds speed and direction for the same time period.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

The period of December 15, 2020 to February 15, 2021 spans the core of the Antarctic summer melt season. During this time, below average surface air temperatures and a very strong Amundsen Sea Low (ASL) prevailed (Figure 2). The ASL has produced strong southward blowing winds, which are warm, along the Bellingshausen coastline and increased the winds from the east along the Amundsen Sea coast. Surface air temperatures along the extensive coast of East Antarctica and a broad region of the adjacent Southern Ocean have been 1 to 1.5 degrees Celsius (2 to 3 degrees Fahrenheit) below average for the core period, relative to the 1981 to 2010 average (Figure 3, top). This is consistent with the near absence of surface melting in the region. Temperatures of about 1 degree Celsius (2 degrees Fahrenheit) above average characterized the southern end of the Peninsula and Siple Coast regions, but temperatures were near average for most of West Antarctica. Wind patterns for the continent show moderate to strong offshore air flow over East Antarctica (Figure 3, bottom).

Trends in Antarctic surface melting

Figure 4. Theses graphs show the melt index area for the Antarctic Ice Sheet and its various regions. Two regions have statistically significant trends, the Antarctic Peninsula and the Amery and Shackleton areas, as well as the Antarctic Ice Sheet as a whole. ||Credit: M. MacFerrin, CIRES and T. Mote, University of Georgia | High-resolution image

Figure 3. Theses graphs show the melt index area for the Antarctic Ice Sheet and its various regions (outlined in Figure 1). Two regions have statistically significant trends, the Antarctic Peninsula and the Amery and Shackleton areas, as well as the Antarctic Ice Sheet as a whole.

Credit: M. MacFerrin, CIRES and T. Mote, University of Georgia
High-resolution image

The melt index is a method of assessing the total surface melt over the entire melt season or the sum of melt area for all days in a season (Figure 3). Melt index values have been generally decreasing over the 1979 to 2020 period. (The 2020 to 2021 melt season has yet to be calculated.) The Antarctic Peninsula value significantly influences the melt index for the continent as a whole. This region is also where the melt index has been declining despite a warming trend in the annual average temperature for much of the past century. The annual average warming trend in turn has been dominated by increases in winter temperature. Surface melting on the Peninsula is strongly controlled by winds from the northwest during the austral summer, which bring warm moist air to the eastern side and produce strong downslope (foehn) winds, which induce extensive surface melting and ponding. Climate factors such as the Southern Annular Mode and the El Niño Southern Oscillation modulate the occurrence and intensity of these northeasterly winds. Other regions of the ice sheet show no clear trend but highlight the erratic extent of melt year to year.

More than one way to break up—for icebergs

Figure 5. Images from a UK Royal Air Force overflight on 05 December 2020 of several of the large fragments of iceberg A68. Image credit, Corporal Philip Dye, RAF Photographer, British Forces South Atlantic Islands. |High-resolution image

Figure 4a. This series of photographs from a UK Royal Air Force overflight on December 5, 2020 shows several  large fragments from iceberg A68. 

Credit: Corporal P. Dye, Royal Air Force Photographer, British Forces South Atlantic Islands
High-resolution image

Figure 6. Image series showing hydrofracture disintegration of iceberg A68E. The berg was located about 100 km northwest of South Georgia Island. Break-up progressed rapidly on 15 February, and the iceberg was rendered into small fragments by 18 February. Credit: NASA | High-resolution image

Figure 4b. These image series show hydrofracture disintegration of iceberg A68E. The iceberg was located about 100 kilometers (62 miles) northwest of South Georgia Island, in the southern Atlantic Ocean. Break up progressed rapidly on February 15, 2021, and the iceberg was rendered into small fragments by February 18. The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on the Terra and Aqua satellites produced these images.

Credit: NASA
High-resolution image

The giant A68 iceberg, roughly the size of Delaware, broke away from the Larsen C Ice Shelf in 2017. Since then, it has slowly drifted northeast. In December, it approached the vicinity of South Georgia Island, in the southern Atlantic Ocean, where atmospheric and ocean conditions are much warmer than around Antarctica. In late December, the iceberg drifted over strong and warm ocean currents, causing the iceberg to break apart and thin.

This is a well-known process that is typical for large icebergs entering warm waters. The large fragments tend to break off along pre-existing lines of weakness that were present in the ice shelf prior to calving. They then begin to shed pieces along their edges as the icebergs drift into warm surface water, 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) above freezing (Figure 4a). This process, known as edge wasting or footloose calving, occurs when warm ocean water melts the iceberg at the waterline. The section of the iceberg above the waterline, or freeboard area, begins to collapse as a result of this undercutting. As it collapses, its weight is lifted off the ice beneath the waterline. This allows the smooth subsurface bench to float upward. Eventually, the bench of ice exerts enough upward force to break away from the edge of the large fragment, creating sliver icebergs. A new paper by colleagues Mark England, Till Wagner, and Ian Eisenmann models this process.

Under continued warm conditions, intense surface melting occurs, and meltwater accumulates in the upper snowpack or as melt ponds. Eventually, the snow layer saturates with water. At this point, fractures in the upper surface of the iceberg can fill with water and rapidly fracture the iceberg, a process called hydrofracture. This process occurs on a very fine spatial scale, and the calved icebergs generally topple, appearing as a blue mush in satellite images (Figure 4b). This process is thought to be responsible for the rapid disintegration of the following ice shelves: Larsen A in 1995, Larsen B in 2002, and Wilkins in 2008.

Adjustment to processing for Antarctica Today

Figure 7. Error analysis of the revised Greenland Today melt detection processing for Antarctica Today. Top graphic, error rate as percentage of comparison weather stations for a given day of the year spanning 2002-2020. Bottom, errors at individual stations for the summer months only showing relationship with elevation. Credit: M. MacFerrin, CIRES and T. Mote, University of Georgia |High-resolution image

Figure 5. The top graph shows the error analysis of the revised Greenland Today melt detection processing applied to Antarctica Today. The error rate is a percentage of weather station comparisons for a given day spanning 2002 to 2020. The bottom graph shows errors at individual stations for the summer months, showing their relationship to elevation.

Credit: M. MacFerrin, CIRES and T. Mote, University of Georgia
High-resolution image

After posting a preliminary map of the 2019-to-2020 melt days in the opening post for Antarctica Today on January 11, several readers noted differences between our assessment and other approaches to estimating surface melt conditions. The initial map of the previous summer’s melt season was based on an identical approach that has been used successfully for Greenland Today. The discrepancy for Antarctica prompted a closer evaluation of several regions, particularly high-elevation areas where melt is extremely rare, such as above the Mertz and Ninnis glacier outlets, and above the West Ice Shelf. These regions were found to have unusual passive microwave emission signatures, notably large annual cycles in the 37 GHz brightness temperature (TB) and lower TB at 18 or 19 GHz than at 37 GHz. The Greenland Today algorithm uses dynamic threshold of the 37 GHz, horizontally polarized TBs. The threshold TB is simulated by a simple microwave emission model for each grid cell, re-evaluated each season, associated with 1 percent liquid water content of the firn (see Mote and Anderson 1995; Mote 2007). With a large annual cycle, false indications of melt can occur. To reduce the false positives, the new processing eliminates grid cells that have an unusual TB variation with frequency unless they exceed the melt threshold by 10 Kelvin or more. A survey of Greenland’s snow characteristics showed few such anomalous grid cells, and these were sparsely distributed. No change is planned to the Greenland processing at this time.

We conducted an error analysis over the years 2002 to 2020 by comparing the satellite-derived melt to observed air temperatures at 131 ground weather stations (74 automated weather stations managed by the University of Wisconsin and 57 UNAVCO meteorology sensors mounted at GPS or seismic stations) (Figure 5). Overall, errors in melt detection by our algorithm were 1.5 percent for the summer months of December, January, and February, when nearly all the melt occurs. These were nearly evenly split by errors of commission (false positive; that is, detecting melt in a grid cell when the local weather sensor does not record temperatures ≥ 0 degrees Celsius for the day; 0.72 percent overall) and errors of omission (false negative; not detecting melt when a surface station indicated a temperature ≥ 0 degrees Celsius that day: 0.78 percent). Errors are dominated by a few locations, often those where nearby stations record persistent warm, near-freezing temperatures, or where stations are located on or near dark rock outcrops. It is likely that a substantial fraction of the errors of omission are due to the specific satellite overpass times versus the daily temperature cycle. Errors of commission may be due to remaining problems associated with unusual firn characteristics at some sites. Another issue can be the difference in temperature measurement between air temperature a few meters above the surface and the snow, particularly on bright sunny days.

Further Reading

Banwell, A. F., R. T. Datta, R. L. Dell, M. Moussavi, L. Brucker, G. Picard, C. A. Shuman and L. A. Stevens. 2021. The 32-year record-high surface melt in 2019/2020 on the northern George VI Ice Shelf, Antarctic Peninsula. The Cryosphere, 15, 909–925. doi:10.5194/tc-15-909-2021.

Barrand, N. E., D. G. Vaughan, N. Steiner, M. Tedesco, P. Kuipers Munneke, M. R. Van den Broeke, and J. S. Hosking. 2013. Trends in Antarctic Peninsula surface melting conditions from observations and regional climate modeling. Journal of Geophysical Research: Earth Surface, 118(1), pp. 315-330. doi:10.1029/2012JF002559.

England, M. R., T. J. Wagner and I. Eisenman. 2020. Modeling the breakup of tabular icebergs. Science Advances, 6(51), p.eabd1273. doi:10.1126/sciadv.abd1273.

Mote, T. L. 2007. Greenland surface melt trends 1973–2007: Evidence of a large increase in 2007. Geophysical Research Letters, 34(22), L22507. doi:10.1029/2007GL031976.

Mote, T. L. 2014. MEaSUREs Greenland Surface Melt Daily 25km EASE-Grid 2.0, Version 1. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi:10.5067/MEASURES/ CRYOSPHERE/nsidc-0533.001.

Mote, T. L. and M. R. Anderson. 1995. Variations in snowpack melt on the Greenland ice sheet based on passive microwave measurements. Journal of Glaciology, 41, 51-60. doi:10.3189/S0022143000017755.

Scambos, T., H. A. Fricker, C. C. Liu, J. Bohlander, J. Fastook, A. Sargent, R. Massom and A. M. Wu. 2009. Ice shelf disintegration by plate bending and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf break-ups. Earth and Planetary Science Letters, 280(1-4), 51-60. doi.org:10.1016/j.epsl.2008.12.027.

Scambos, T., Sergienko, O., Sargent, A., MacAyeal, D. and Fastook, J., 2005. ICESat profiles of tabular iceberg margins and iceberg breakup at low latitudes. Geophysical Research Letters, 32(23). doi:10.1029/2005GL023802.

Wagner, T. J., P. Wadhams, R. Bates, P. Elosegui, A. Stern, D. Vella, E. P. Abrahamsen, A. Crawford and K. W. Nicholls. 2014. The “footloose” mechanism: Iceberg decay from hydrostatic stresses. Geophysical Research Letters, 41(15), 5522-5529. doi:10.1002/2014GL060832.

Announcing Antarctica Today

Greenland Today expands to cover the Antarctic melt season

Antarctic Cumulative Melt Days, 2019 to 2020 Melt Season

Figure 1. This sample map of the Antarctic Ice Sheet shows the total number of surface melt days for the 2019 to 2020 melt season. The new Antarctic Today will show daily images of the melt season.

Credit: M. MacFerrin, Cooperative Institute for Research in Environmental Sciences (CIRES) and T. Mote, University of Georgia
High-resolution image

Antarctic and Peninsula melt extent

Figure 2. These sample graphs show daily area in square kilometers of surface melting for the Antarctic Ice Sheet (above) and the Antarctic Peninsula (below) during the 2019 t0 2020 melt season. The new Antarctic Today will update these daily data to compliment the National Snow and Ice Data Center Greenland Today analysis.

Credit: M. MacFerrin, Cooperative Institute for Research in Environmental Sciences (CIRES) and T. Mote, University of Georgia
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Regions of Analysis for Antarctica Today

Figure 3. The left map shows the analysis regions used for the Antarctic Ice Sheet Today reports. The regions are based on drainage basins as defined in Shepherd et al. 2012, but clustered in multi-basin regions based on the climate patterns driving surface melt. Grid cells with mountain areas (shown as black patches) are not included in the mapping. The lines enclosing the ice sheet are the current outer ice edge and grounding line, or the line where the ice begins to float on the ocean. The right map shows the average annual number of melt days for the November to March melt season for 1989 to 2020 (30 seasons).

Credit: M. MacFerrin and T. Scambos, Cooperative Institute for Research In Environmental Sciences
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As the Southern Hemisphere enters into the full of swing of summer, parts of the Antarctic Ice Sheet are experiencing surface melting. Until now, NSIDC’s Greenland Today near-real-time analysis has only covered the melt season for the Greenland Ice Sheet. At the other end of the world, the Antarctic Ice Sheet will also have a voice, with frequent posts regarding its climate and surface melt events. Greenland Today will be releasing a beta test for Antarctica Today, covering surface melting using a modified version of the passive-microwave algorithm used for Greenland Today. As a counterpart to the Northern Hemisphere’s Ice Sheet, Antarctica Today will show near-real-time analysis of summer surface melting, and important weather and climate events.

Data visualization and graphics similar to the Greenland Today graphics (Figures 1 and 2) will be presented but with some variations as the Antarctica Today beta versions are produced using external research processing code.

We plan to report on the 2020 to 2021 Antarctic melt season in late January and mid-March, and other times if events warrant, including regional assessments and some comparisons of this year’s melt with past years. Antarctica’s far larger extent makes it necessary to consider regional trends and melt progress separately. We have based the regional maps on ice sheet drainage basins centered on regions where some surface melting occurs each year (Figure 3). Antarctica Today uses the same processing methods as Greenland Today, modified for Antarctic snow conditions and tuned by comparison to several surface weather stations.

Further reading

Shepherd, A., E. R. Ivins, A. Geruo, V. R. Barletta, M. J. Bentley, S. Bettadpur, K. H. Briggs, D. H. Bromwich, R. Forsberg, N. Galin, and M. Horwath. 2012. A reconciled estimate of ice-sheet mass balance. Science338 (6111), 1183-1189, doi:10.1126/science.1228102.

Acknowledgements

Antarctica Today is produced by the National Snow and Ice Data Center (NSIDC), which is part of the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder. The sea ice data are from the NASA Snow and Ice Distributed Active Archive Center (DAAC).

Antarctica Today (beta) was developed by Mike MacFerrin¹, Thomas Mote², and Ted Scambos¹.

1: Earth Science and Observation Center/Cooperative Institute for Research in Environmental Sciences (ESOC/CIRES)
2: University of Georgia

Greenland’s 2020 melt season in review

The 2020 melt season in Greenland is over, finishing thirteenth for cumulative melt-day extent in the 42-year satellite record. Melt extent was greater than any year prior to 2002, with about 70 percent of the ice sheet experiencing some melting. Melting was moderately intense in the northeastern region but less so in the southwest, where in recent high-melt years the ice sheet has been losing mass and exposing bare ice. Much of the upper elevation areas of the ice sheet saw no melting this year. The balance between snow and rain input and melt runoff indicates a small net loss of ice this year. This does not include the imbalance caused by ice flow.

Overview of conditions

Greenland Melt for Summer 2020

Figure 1. The top left map of the Greenland Ice Sheet shows the total number of surface melt days from January 1 through October 31, 2020. The top right map shows the difference between total 2020 melt days and the number of 1981 to 2010 average melt days from April 1 through October 31. The lower graph shows daily area in square kilometers of surface melting from April 1 to October 31, 2020, with daily melt extent trends for the preceding four years.

Credit: National Snow and Ice Data Center/T. Mote, University of Georgia
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cumulative melt days area for 2020

Figure 2. This graph shows the cumulative melt day area for Greenland for 2020, 2019, 2018, and 2012, as well as the 1981 to 2010 average and typical ranges of cumulative melt day area.

Credit: National Snow and Ice Data Center
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The total aerial extent of surface melting (total melt-day extent) through October 31 is slightly above the 1981 to 2010 average at 23.10 million square kilometers (8.92 million square miles) for 2020 versus 22.00 million square kilometers (8.49 million square miles) for the 1981 to 2010 average. Melting was intense in the northeastern section of the ice sheet, with 20 to 25 additional melt days than average, and moderately intense in the southwestern section of the ice sheet with 10 to 20 additional melt days (Figure 1). The peak melt day for 2020 was on July 10, when 551,000 square kilometers (213,000 square miles), or 34 percent of the ice sheet surface, melted. There were two later melt events of note, on August 20 when extensive areas in northwestern Greenland melted totaling just over 20 percent of the ice sheet, and a late event on October 17, limited to the southwestern ice sheet totaling under 3 percent of the ice. Overall the pace of melt during the 2020 season was close to average until late June when a moderately prolonged period of above-average melt added to the cumulative total, bringing it to the upper part of the interquartile range (Figure 2). Thus, the 2020 total melt extent tracked at a level larger than about 75 percent of past years in the satellite record after late June.

Conditions in context

GrnToday_Nov20_Fig3wx

Figure 3. The top plot shows average air temperature as a difference from the 1981 to 2010 average at the 700 mb level, or about 10,000 feet above sea level, from June 1 through August 31, 2020. The bottom plot shows height difference from average for the 700 mb pressure level in the atmosphere for the same period.

Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research
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Figure 4. Cumulative degree days (the sum of the difference between the freezing point, 0 degrees Celsius, and the maximum temperature each day for the spring-summer melt season for two automatic weather stations in Greenland, at Nuuk (NUK_L) and Thule (THU_L). ||Credit: Programme for Monitoring of the Greenland Ice Sheet (PROMICE) | High-resolution image

Figure 4. Cumulative degree days (the sum of the difference between the freezing point, 0 degrees Celsius, and the maximum temperature each day for the spring-summer melt season for two automatic weather stations in Greenland, at Nuuk (NUK_L) and Thule (THU_L).

Credit: Programme for Monitoring of the Greenland Ice Sheet (PROMICE)
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Air temperatures above Greenland were generally near average over the summer months this year (Figure 3). Higher-than-average temperatures, with up to 3 degrees Celsius (5 degrees Fahrenheit) were limited to the far northern flank of the ice sheet, and significantly lower-than-average temperatures of 1.5 to 2 degrees Celsius (3 to 4 degrees Fahrenheit) near the Scoresby Sund in east-central Greenland. Though local surface winds can be quite high under certain conditions, air pressure patterns over the ice sheet indicated generally light regional winds that favored a westward to southwestward flow. Air off the far northern Atlantic Ocean in the Norwegian Sea swept in across the ice sheet. This pattern of temperature and pressure was remarkably consistent through all the individual months of June, July, and August.

A look at weather station data along Greenland’s west coast reflects the regional temperature trends (Figure 4). Nuuk, the capital of Greenland on the central southwestern coast, had summer temperatures very close to average for that region. Thule, near a large US military base in northwestern Greenland, had a much warmer than average summer, but was still cooler than Nuuk, which is nearly 1,500 kilometers (580 miles) to its south.

Greenland still on a diet

Surface mass balance for Greenland 2019-2020 relative to a 1981-2010 reference period

Figure 5a. This graph shows surface mass balance (SMB) for Greenland’s 2019 to 2020 autumn-winter-spring season (red line) relative to a 1981 to 2010 reference period. SMB is the sum of snowfall and rainfall minus any evaporation or runoff. Several recent high-melt years are shown for comparison. The estimates come from a model based on daily weather measurements.

Credit: X. Fettweis, Université of Liège, Belgium/MARv3.11 regional climate model
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Input and output for SMB 1978-2020

Figure 5b. This bar graph show net surface balance as a result of input vs output into the ice sheet for the 1978 to 2020 period based on reanalysis of weather data and snow-atmosphere model of process from MARv3.11. Net snow and rain input are shown in yellow, melt and evaporation loss in orange, and net surface balance in green. The 2020 season, which runs from September 1, 2019 to August 31, 2020 in this analysis, shows a net loss smaller than many recent years, but larger than most years in the previous century. The 10-year average line includes estimates from before 1978 on the left edge of the graph.

Credit: X. Fettweis, Université of Liège, Belgium/MARv3.11 regional climate model
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Net surface mass balance (SMB), which is the snow and rain input minus evaporation and melt runoff, was only slightly less than average at 314 billion tons, or 56 billion tons below the 1981 to 2010 average, according to the MARv3.11 climate model (Figure 5a). This can be compared to the major melt and ice loss years of 2012, 2019, and others in the last decade with values between 225 and 325 billion tons below average (Figure 5b). The 2020 regional pattern had low SMB all along the western side of the ice sheet but near average to slightly above average along most of the eastern coastal areas.

Greenland’s glaciers: more to their change than just faster flow

Figure 6. (a) White and colored areas show the extent of the region where early ice flow maps (1985-1990) can be compared with images acquired up to 30 years later. Observations around the ice sheet margin (b-d) show new details about how the ice sheet is responding (faster flow in red, slower in blue). Responses include narrowing of fast flow regions, rerouting of ice flow, and abandonment of some glacier outlets. ||Credit: Moon, T. A., et al., 2020, Journal of Geophysical Research: Earth Surface| High-resolution image

Figure 6. (a) White and colored areas show the extent of the region where early ice flow maps (1985-1990) can be compared with images acquired up to 30 years later. Observations around the ice sheet margin (b-d) show new details about how the ice sheet is responding (faster flow in red, slower in blue). Responses include narrowing of fast flow regions, rerouting of ice flow, and abandonment of some glacier outlets.

Credit: Moon, T. A., et al., 2020, Journal of Geophysical Research: Earth Surface
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With a growing record of satellite imagery and advances in image processing, scientists are now able to better explore the changes to Greenland’s coastal area in the last three decades. A new paper by our colleagues Twila Moon, Alex Gardner, Bea Csatho, Ivan Parmuzin, and Mark Fahnestock analyzes how ice outflow speed and surface melting have increased. Every year since 1998, the ice sheet has overall lost ice. Satellite sensor improvements, such as on Landsat 7 and 8, and improvements in image processing for ice flow mapping (see ITS_LIVE) have created an improved set of maps for documenting changes in Greenland’s ice outflow. These maps reveal substantial reconfigurations of several major glaciers (Figure 6). For many fast-flowing glaciers, the research team found that the central channel of fast flow has sped up, but the edges of the channel have slowed, effectively narrowing the width of the fast flow area. Researchers also see evidence for ice flow rerouting and even abandonment of some glacier outlets. While thinning ice and retreats from the ice edge change the ice sheet, the shape of the land beneath the ice remains mostly unchanged. In some areas the ice cannot flow over the landscape via the historical pathways. This reconfiguration of the ice sheet has important implications for other elements of the Greenland system, such as the flow of water beneath the ice sheet, and the movement of sediment and nutrients into the fjords. The new data collected by ITS_LIVE are allowing researchers to characterize and understand what rapid deglaciation looks like on scales that matter for wildlife, fisheries, infrastructure, and communities.

Further reading

Moon, T. A., A. S. Gardner, B. Csatho, I. Parmuzin, and M. A. Fahnestock. 2020. Rapid reconfiguration of the Greenland Ice Sheet coastal margin. Journal of Geophysical Research: Earth Surface, 125, doi:10.1029/2020JF005585.

Tedesco, M. and X. Fettweis. 2020. Unprecedented atmospheric conditions (1948–2019) drive the 2019 exceptional melting season over the Greenland ice sheet. The Cryosphere, 14, 1209–1223, doi:10.5194/tc-14-1209-2020.

The 2020 Greenland Ice Sheet SMB simulated by MARv3.5.2 in real time

Polar Portal’s Greenland surface conditions

Programme for Monitoring of the Greenland Ice Sheet (PROMICE)

Acknowledgements

Jason Box, Geological Survey of Denmark and Greenland (GEUS) in Copenhagen, Denmark

Xavier Fettweis, Université of Liège in Belgium, providing the MARv3.11 model results

Twila Moon, National Snow and Ice Data Center

Thomas Mote, University of Georgia

Daily updates are suspended for winter

Daily melt extent mapping is suspended for the winter. Calibration of yearly melt detection requires analysis of the springtime snow conditions by a separate program. See our March 18, 2013 post for more discussion of melt calibration.

Our interactive chart supports a retrospective look at past Greenland melt seasons. This will remain available for our users.

We will resume the daily image updates in April 2021.