Europe’s warm air spikes Greenland melting to record levels

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Warm air from Europe’s heat wave reached Greenland on July 29 and 30, setting temperature records at Summit Station and melting about 90 percent of the ice sheet surface from July 30 to August 3. Melt runoff was estimated at 55 billion tons during the interval, or about 40 billion tons more than the 1981 to 2010 average for the same time period. Overall, melting this July was much higher than average, leading to more extensive bare ice and flooded snow areas.

Overview of conditions

Figure 1a. The top left map shows melt extent for Greenland on July 31, the peak of the recent warm event. The map includes temperatures at local noon for that day from several Programme for Monitoring of the Greenland Ice Sheet (PROMICE) weather stations. The top right map shows the total number of melt days for January 1 to August 3, 2019. The bottom panel shows the melt area day-by-day for 2019 (blue) and several other high-melt years.

Credit: National Snow and Ice Data Center
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Figure 1b. This graph shows the cumulative surface melting area for 2019 and several of the most recent years.

Credit: National Snow and Ice Data Center
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A rapid increase in surface melting on the Greenland ice sheet began on July 30 and continued through August 3, covering primarily the central and northern areas of the ice sheet on both the east and west ice sheet slopes. On July 30 and 31, melting reached the Summit Camp area of the ice sheet, corroborated by both air temperature from the National Oceanic and Atmospheric Administration (NOAA) weather station at Summit and the passive-microwave melt analysis. Peak melt area occurred on July 31, with just over 60 percent of the ice sheet surface experiencing melt (Figure 1a). Over the course of the five-day event approximately 90 percent of the surface of Greenland reached the melting point at least once.

The daily sum of melt area in July was 397,560 square kilometers (154,500 square miles), well above the 1988 to 2017 average of 337,945 square kilometers (130,481 square miles). The 1988 to 2017 range is a 30-year record of daily melt mapping for Greenland in summer. Melt area mapping from 1979 to 1987, on the other hand, recorded every other day, using a earlier passive microwave satellite.

Cumulatively, the 2019 season sum of melt area for every day is tracking well behind 2012, the satellite-era record for total melt-day area, and slightly behind 2016 (Figure 1b). However, total ice mass loss for 2019 is nearly equal to 2012 because of low winter snowfall. Early melting of the surface in 2019 quickly removed the snow accumulation from winter, and deeper melting this month has eroded older snow and ice over large areas of the western side of Greenland.

Conditions in context

Figure 2a. Top, Average air temperature difference from the 1981-2010 average at the 700 hPa level, or about 10,000 feet above sea level, for 30 July – 03 August, 2019. Bottom, average sea level pressure (estimated over land areas) for the same period. (NCEP Reanalysis data, National Center for Atmospheric Research)

Figure 2a. The top plot shows air temperature as a difference from average for the 1981 to 2010 reference period at the 700 hPa level (about 10,000 feet above sea level) for July 30 to August 3, 2019. The bottom plot shows the average sea level pressure (estimated over land areas) for the same period.

Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research
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Evolution of heat wave from Europe to Arctic

Figure 2b. This series of images from the atmospheric circulation model shows the evolution of a weather pattern from July 25 to July 31, 2019.

Credit: Global Forecast System (GFS)/National Centers for Environmental Prediction (NCEP)/US National Weather Service
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Surface air temperatures during the warm event over Greenland peaked to 12 degrees Celsius (22 degrees Fahrenheit) above the 1981 to 2010 reference period, and averaged 3 to 9 degrees Celsius (5 to 16 degrees Fahrenheit) above the reference period over nearly the entire ice sheet for the five-day period. High pressure was centered over the ice sheet during the event.

Extreme warm air conditions were present over western Europe in late July, as desert air from the Sahara moved northward. Following the record high temperatures in France, the Netherlands, and Germany, counterclockwise airflow around a low pressure in the North Atlantic brought the warm air mass from Scandinavia to Iceland and then to Greenland. As warm air arrived at Summit Station, Greenland, a prolonged period of near-freezing to above-freezing temperatures occurred on July 30 and 31. In a place where the sun sits low on the horizon at night, these temperatures are unprecedented in the period of observations for this site, which began in 1987. Temperatures dropped further on the night of July 31, but came close to melting again on August 1. With air incoming from the east and some cloudiness in the south of Greenland, melting was amplified on the western side by heating from air compression in downslope winds, increasing the surface melting and runoff. The westward movement of the warm air mass is unusual. Most recent warm events, such as the widespread melting earlier this year, and in July and August of 2012, were a result of air masses coming from the southwest and up along the western Greenland coast.

Losing billions of tons of ice per day

Figure 3. Top graph, estimated snow and ice gain or loss for the Greenland Ice Sheet for several recent years, in billions of tons, relative to the average of the reference period, 1981-2010; lower two graphs show estimated melt runoff (upper graph) and total amount of melt (lower graph), in billions of tons per day for several recent years. Dashed lines indicate forecast values for early August. Model results from the MAR 3.9 model provided by Xavier Fettweis.

Figure 3a. The top graph shows estimated snow and ice gains or losses for the Greenland ice sheet for several recent years, in billions of tons, relative to average for the 1981 to 2010 reference period.

Credit: X. Fettweis, Université of Liège, Belgium/MAR regional climate model
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Figure 3b. lower two graphs show estimated melt runoff (upper graph) and total amount of melt (lower graph), in billions of tons per day for several recent years. Dashed lines indicate forecast values for early August. Model results from the MAR 3.9 model provided by Xavier Fettweis.

Figure 3b. These two graphs show estimated melt runoff, for the upper graph, and total amount of melt, for the lower graph, in billions of tons per day for several recent years. Dashed lines indicate forecast values for early August. Total melt amount over the ice sheet is higher than melt runoff because in many areas high up on the ice sheet, small amounts of melt seep into the snow and re-freeze, leaving the mass of the ice sheet unchanged.

Credit: X. Fettweis, Université of Liège, Belgium/MAR regional climate model
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Our colleague, Xavier Fettweis at the Université of Liège, Belgium, developed a Greenland ice and climate model that provides estimates of mass gained or lost by snowfall and melt (not including ice lost from the outflow of glaciers) (Figure 3a). To date, 2019 is tracking the record high melt volume and ice loss of 2012 almost exactly, with about 40 days left in the melt season. At present, Greenland has lost a total of over 250 billion tons from melt runoff (and low total snowfall earlier in the season). Daily melt amounts were 12 to 24 billion tons through the five-day event, about 6 to 18 billion tons above the rates typical of the 1981 to 2010 reference period for these days. Total runoff for the five-day period was 10 to 12 billion tons per day, or 5 to 7 billion tons per day above average rates (Figure 3b). The ice sheet lost approximately 55 billion tons through melt runoff during the event.

At summit: The highest temperatures in the past 12 years

Air temperatures at Summit Station, Greenland

Figure 4. This graph shows temperatures at 2 meters (6.5 feet) above the snow surface from Summit Station, Greenland, for the past 12 years (2008 to 2019, inclusive) for June 1 to August 15. Above-freezing temperatures over a ten-minute period have only been reached at Summit Station on three days during this period: July 11, 2012, and July 30 and 31, 2019. Data provided by NOAA’s Earth System Research Laboratory, Global Monitoring Division.

Plot prepared by Christopher Shuman and Michael Schnaubelt, University of Maryland Baltimore County
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The NOAA 2-meter air temperature data from Summit Station on the July 30, 2019 was at or above freezing for more than 11 hours, a record in the last 12 years, which has seen a period of increased temperatures overall. Furthermore, this melting event on July 30 also sets the record for the preceding century. Prior to 2012, melt layers at summit have been absent since 1889, and only appear again 680 years earlier.

Only two other melt events occurred here in the last 12 years, both shorter: On July 11, 2012 melting lasted for about 6.5 hours and on July 31, 2019 for more than five hours. The highest 1-hour average of above-freezing temperatures were set in 2012 at 0.79 degrees Celsius (33.4 degrees Fahrenheit) and in 2019 at 0.92 degrees Celsius (33.7 degrees Fahrenheit). Cooling on the evening of July 30 to 31 was minimal, to approximately -2.5 degrees Celsius (27.5 degrees Fahrenheit), and an unprecedented second day of above-freezing maximum temperatures occurred on July 31, 2019, when temperatures were above freezing for more than five hours and reached a maximum of 1.1 degrees Celsius (34.0 degrees Fahrenheit).

Deep blue ice and darker snow

Figure 5a. These maps of Greenland show albedo, or the brightness and reflectivity, of the ice sheet surface (blue-white areas) on July 29 and August 1, 2019, using Sentinel-3 Ocean and Land Color Instrument (OLCI).

Credit: Jason Box, Geological Survey of Denmark and Greenland (GEUS)
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Figure 6. Landsat 8 of an area of the western Greenland Ice Sheet on August 2nd in the Jakobshavn area near the upper edge of the bare ice region, showing dark exposed ice, melt ponds, some residual winter snow, and tundra near the coast. Enhanced true color image from Path 009, Row 011, 180 km (112 miles) on a side; north is marked.

Figure 5b. This enhanced true-color Landsat 8 image shows an area of the western Greenland ice sheet on August 2 in the Jakobshavn area near the upper edge of the bare ice region. Dark exposed ice, melt ponds, some residual winter snow, and tundra are visible near the coast. The image is of Path 009, Row 011, 180 kilometers (112 miles) on a side; north is marked.

Credit: US Geological Survey and NASA
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As the melt event progressed, a wider area of dark bare ice was exposed (Figure 5a). However, a brief snow event just prior to the major melt period left some areas slightly brighter and more reflective, reducing the total area that melted relative to the 2012 event (60 percent in 2019 versus 70 percent of the ice sheet in 2012). Jason Box of the Geological Survey of Denmark and Greenland (GEUS) provided the new albedo, or solar reflectance, mapping product.

A Landsat image of the western flank of Greenland acquired on August 2 shows dark blue exposing older bare ice, with a darker band of dust-laden ice—formed during the last ice age—and wet snow and melt ponds at higher elevations along the right side of the image. 

July run-off: whitewater

Figure 7. Top, runoff from the ice sheet near the Greenland capital of Nuuk. The bottom image shows the location of the monitoring station.

Figure 6. The top photograph shows runoff from the Greenland ice sheet near the Greenland capital of Nuuk. The bottom image shows the location of the monitoring station.

Credit: Irina Overeem
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Water from the Greenland ice sheet contains rock flour, or very finely ground mineral dust, from bedrock erosion by the flowing ice. In the Naajatkuat River, a meltwater river in the Nuuk fjord region, a measurement station above the rapids monitors river levels (Figure 6). The image of runoff was taken during an earlier warm week, July 12 to 14, in southwest Greenland when daytime high temperatures at this low coastal elevation were 19 degrees Celsius (66 degrees Fahrenheit).

Irina Overeem has been monitoring river levels at the flood station at this location since 2011. At the time the picture was taken, the river level was 5.3 meters (17 feet) below the sensor. At the highest level during the exceptional melt in 2012, the water reached to 2.5 meters (8.2 feet) below the sensor. As of this post, water levels for the peak of the July to August 2019 event had not been recovered from the station. 

Further reading

Hanna, E., X. Fettweis, S. H. Mernild, J. Cappelen, M. H. Ribergaard, C. A. Shuman, K. Steffen, L. Wood, and T. L. Mote. 2013. Atmospheric and oceanic climate forcing of the exceptional Greenland ice sheet surface melt in summer 2012. International Journal of Climatology, 34, 4, 1022–1037. doi:10.1002/joc.3743.

Shuman, C. A., K. Steffen, J. E. Box, and C. R. Stearns. 2001. A dozen years of temperature observations at the summit: Central Greenland automatic weather stations 1987–99. American Meteorological Society, 741-752. doi:10.1175/1520-0450(2001)040<0741:ADYOTO>2.0.CO;2.

Trusel, L. D., Das, S. B., Osman, M. B., Evans, M. J., Smith, B. E., Fettweis, X., McConnell, J. R., Noël, B. P. and van den Broeke, M. R. 2018. Nonlinear rise in Greenland runoff in response to post-industrial Arctic warming. Nature, 564(7734), 104. doi:10.1038/s41586-018-0752-4.

Acknowledgements

Xavier Fettweis, Université of Liège in Belgium, for providing the MAR 3.9 model results.

Christopher A. Shuman (University of Maryland Baltimore County (UMBC) Joint Center for Earth Systems Technology at NASA Goddard Space Flight Center (GSFC)) and Mike Schnaublet (UMBC Physics) for producing the “Air Temperatures at Summit, Greenland” graph from data provided by NOAA’s Earth System Research Laboratory, Global Monitoring Division.

Jason Box, Geological Survey of Denmark and Greenland (GEUS) in Copenhagen, Denmark, for producing albedo measurements from a variety of sources for the Greenland ice sheet.

Irina Ovreem and Jasmine Hansen,The Institute of Arctic and Alpine Research (INSTAAR) and the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder (CU). The Research and Innovation Office (RIO), INSTAAR, and CU Boulder funded this field season.

A record melt event in mid-June

Between June 11 and 20, an extensive area of the Greenland ice sheet surface melted. At its peak on June 12, thawing climbed from the western and eastern coasts to elevations above 3,000 meters (9,800 feet). High air pressure and clockwise circulation around the island brought warm air from the south and sunny conditions. While several recent years have had similar early widespread melt events, the event of June 11 to 20 reached a peak of just over 700,000 square kilometers (270,000 square miles), setting a record for this early in the melt season. Models estimate the amount of melted ice at approximately 80 billion tons for that period.

Overview of conditions

Figure 1. The top left map shows the melt extent on June 12, the peak of the recent warm event. The top right map shows the difference between the average number of melt days for January 1 to June 20, relative to the 1981 to 2010 average, and the amount of melting that has occurred this year. The lower panel shows the melt area day-by-day for 2019 and several other years with mid-June excursions in melting, showing that the event of 2019 was a record surface melt area for June 12. 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
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Following a relatively dry winter and warm spring for Greenland, a major surface melt episode occurred between June 11 and 20. The maximum area of melt occurred on June 12, at 712,000 square kilometers (275,000 square miles). Melting was detected around the entire coast except the far southern tip of the ice sheet, and extended well inland in both the west central and east central regions, nearly to the summit. The eastern and northeastern coastal areas also melted extensively.

Melting in Greenland through the end of spring has been significantly higher than the 1981 to 2010 average, with several areas exceeding 10 days of additional melt above the average, and a few regions with more than 20 days. Only the southernmost tip of the island and a region along the southwestern side of the ice sheet are below the average to date.

Conditions in context

Figure 2a. The top plot shows differences in air temperature relative to the 1981 to 2010 average at the 700 hPa level, or about 10,000 feet above sea level, for June 11 to 20. The bottom plot shows the average sea level pressure (estimated over land areas) for the same period.

Credit: NCEP Reanalysis data, National Center for Atmospheric Research
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Figure 5.

Figure 2b. These true-color images from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) sensor show sunny conditions over Greenland on June 11 to 13, left to right. The band of greyish-white along the western coast is the ablation area, or exposed bare ice area where the ice sheet is losing mass, as seen in the NASA WorldView MODIS corrected reflectance true-color images.

Credit: NASA WorldView
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During the June 11 to 20 melt event, warm conditions extended over the entire island and particularly along the eastern coast with temperatures up to 9 degrees Celsius (16 degrees Fahrenheit) above the 1981 to 2010 average. High air pressure across the island drew warm air from northeastern Canada across the island. Along the eastern coast, warm winds from the west flowed downhill. Sunny conditions across nearly the entire island were seen on June 11, 12, and 13 (Figure 2b), increasing melt.

Rapid drop in albedo along the western flank

GT_JuneMeltSpike_CSfig3

Figure 3. Surface brightness in the top two images, derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), shows the rapid darkening of the western edge of the ice sheet. The left image shows May 15, while the right June 17. The recent extensive melt event exacerbated early melting in the ablation area, where bare ice becomes exposed by early warming. Shortwave ‘white sky’ albedo, or the fraction of light reflected upward from the surface, for the wavelength range is 0.3 to 5.0 micrometers. Credit: C. Schaaf and A. Elmes, University of Massachusetts Boston.

The bottom photograph shows dark exposed ice, melt ponds, and residual winter snow on June 12 near the upper edge of the bare ice region on the Greenland ice sheet.

Credit: K. Atkinson
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In our previous post, we noted that low snowfall over western Greenland and early spring warming led to an early beginning to the 2019 melt season. Loss of this thin snow cover has rapidly darkened the surface of the western coast by exposing the bare ice of the ablation area of the ice sheet earlier than usual (Figure 3). The ablation area is the area of a glacier where more glacier mass is lost than gained, and where old snow has eroded leaving bare ice. Fresh powdery snow reflects about 80 percent of solar energy, while bare clean ice reflects between 40 to 50 percent, depending on the dust content, which can darken its surface. This early exposure of bare ice increases the pace of meltwater production by allowing the darker ice surface to absorb more solar radiation. An image acquired by one of our readers from a commercial jet crossing southern Greenland shows the edge of the bare ice zone, with darkened snow and bare ice, along with some remaining snow from the previous winter.

A very warm spring

Figure 4. The graph shows air temperature for spring 2019 from the EastGRIP Automated Weather Station compared to the average of the preceding three years. Although the EastGRIP station was not in the area of surface melting in June melt event, the trend shows the unusually warm conditions for this spring.

Credit: J. Box, Programme for Monitoring of the Greenland Ice Sheet (PROMICE)
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A warm spring has heated the Greenland snowpack, preconditioning it for early melting. Although early-season melting (prior to the June 12 event) was not record breaking, the upper snow layers are more likely to thaw as summer proceeds.

Estimated total melt and meltwater runoff from a climate model

Figure 5. The upper plot estimates meltwater runoff from the Greenland ice sheet for several warm years and the 1981 to 2010 reference period average and maximum, in billions of tons per day. Model estimate for 2019 is plotted through 28 June. The lower plot estimates the total melt for the same years and reference period. Total melt is greater because a large fraction of the melt over snow-covered areas drains into the snow and refreezes.

Credit: X. Fettweis, Université of Liège, Belgium/MAR regional climate model
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A model of Greenland climate, using inputs of weather data and forecasts as well as the physical properties of the ice sheet, has estimated the total amount of melt during the extensive melt event. The model also estimated the total amount of melt that flowed off the ice sheet and into the ocean (Figure 5). Both total melt and meltwater runoff set new records for several of the melt event dates. Total melt from June 11 to 20 was about 80 billion tons, of which approximately 30 billion tons ran off the ice into the ocean (or was stored temporarily in lakes).

Further reading

The 2017 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)

April and May: Above average, but nothing to write Nome about

Surface melting on the Northern Hemisphere’s largest mass of ice began during the second week of April, with several significant melting episodes at the end of the month and into early May. Warm conditions over the ice sheet and winds from the east were prevalent for the two-month period. While significant, and above average for the 1981 to 2010 reference period, the melting extent has been comparable to previous years spanning 2010 to 2018.

Overview of conditions

Figure 1. The number of melt days in 201X on the Greenland Ice Sheet exceeded XXX for low elevation areas along the southwestern coast, and values above XXXdays were seen in the far north and southeastern coastal areas. 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

Figure 1. This map shows the cumulative melt days for the 2019 melt season through May 31, 2019. 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
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Figure 2. The graph above shows the daily extent of melt during 2013 on the Greenland Ice Sheet surface as a percentage. The 1981 to 2010 average is shown by a blue dashed line. The gray area around this average line shows the two standard deviation range of the data. Data are from the 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

Figure 2. The top plot shows Greenland’s daily melt extent with the percentage of the ice sheet experiencing melt for each day in 2019. The red line depicts April 1 to May 31, the dashed blue line the 1981 to 2010 average, and the grey areas show the range of 90 percent (pale grey) and 50 percent (dark grey) of all years during that period. The bottom plot shows daily melt areas in square kilometers from April 1 to May 31 for 2010 (black), 2011 (light green), 2012 (light orange), 2013 (lavender), 2014 (red), 2015 (purple), 2016 (brown), 2017 (dark orange), 2018 (dark green), and 2019 (blue). 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
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Fig3_ClimateReanalzer_12Apr

Figure 3. This map shows precipitation on April 12, spanning the North Atlantic, Arctic Ocean, and adjacent continental areas. This basic pattern recurred several times in late April and May.

Credit: NOAA, Climate Analyzer
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The number of surface melting days was well above the 1981 to 2010 average for the beginning of the 2019 Greenland melt season, particularly along the southeastern coast. Surface melting was detected up to 26 out of the 61 days between April 1 to May 31. A narrow band of melting was also present along the western coast, from the southern tip of Greenland to the region around Thule in the northwest, exceeding 20 days in some locations. This represents an early onset, but not an unprecedented extent or intensity relative to recent years.

On May 6, melt extent was the highest observed for that day in the 40-year satellite record by a small margin. However, greater melt events—both earlier and later than May 6—have been observed in the past. The May 6 event extended over the southeastern flank of the ice sheet.

More extensive melt periods were seen from mid- to late April and again in early May when clouds bringing warm air and moisture blanketed the southeastern coast. This was attributed to low pressure in the Irminger Sea, between Iceland and Greenland, driving air from the east and south onto the steeply sloping ice sheet, resulting in snowfall and sometimes rain.

 

Conditions in context

Figure 4. The top plot shows the departure from average air temperature over Greenland at the 700 hPa level, or about 10,000 feet above sea level, for April and May 2019 as compared to the 1981 to 2010 average. The bottom plot shows average sea level pressure (estimated over land areas) for the same period.

Credit: NCEP Reanalysis data, National Center for Atmospheric Research
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Figure 5. These maps are the result of a climate model simulating surface mass balance (SMB) departure from average for Greenland up to June 2, 2019. SMB is the net sum of snowfall and rainfall, minus any evaporation or runoff. The reference period is 1981 to 2010.

Credit: Xavier Fettweis, Université of Liège, Belgium/MAR regional climate model
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It was unusually warm over nearly the entire ice sheet relative to the 1981 to 2010 reference, notably over the northern half of the island, where temperatures were more than 4 degrees Celsius (7 degrees Fahrenheit) above average. Over most of the island, this still means conditions were well below freezing, but along the western coast and southeastern coast, temperatures rose to the melting point frequently. Sea level pressure was higher than average along the northeastern coast, with low pressure centered (on average for the two months) off the southeastern tip of the island, and southwest of Iceland. This set up a pattern of winds blowing from the east, off the ocean, and supported significant water vapor transport and large snow accumulations. Winds from the east are not unusual for this region, and tend to bring warm and snowy conditions, and sometimes rain.

Snowfall and surface mass balance, or the combination of snow and rain, minus any evaporation or runoff, are near average, recovering from a relatively dry winter. This recovery is related to a strong influx of moisture-carrying air from the south and east of Greenland to its southeastern coast. However, the recovery is limited to that area, and the rest of Greenland to the north and west are well behind their typical snowfall totals for this time of year. Notably, some net runoff (ice loss for the ice sheet) has already begun along the central western coast resulting from the early onset of the melt season and the low winter snowfall.

Slowing of Greenland’s largest glacier

Figure 6. Ice flow speed for a point near the front of Jakobshavn Isbrae, the largest glacier in Greenland, derived from a number of satellite data sets; and ocean temperatures from 250 m depth (about 825 feet below the surface) measured in Disko Bay, located just in front of the glacier fjord. Jakobshavn Isbrae is near the center of the western coast of Greenland.

Figure 6. The top graph shows ice flow speed for a point near the front of Jakobshavn Isbrae, the largest glacier in Greenland, derived from a number of satellite data sets. The bottom graph shows ocean temperatures from 250 meters depth (about 825 feet below the surface) measured in Disko Bay, located just in front of the glacier fjord. Jakobshavn Isbrae is near the center of the western coast of Greenland.

Credit: Khazendar et al., 2019 Nature Geoscience
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A recent paper documents that Greenland’s largest glacier, Jakobshavn Isbrae, has slowed dramatically in recent years in response to cooling of ocean temperatures in the waters near the coast. The study uses ice flows determined from satellite spanning 19 years (2000 to 2018) and ocean temperature from a number of measurements over that time. Ice flow speeds in the selected location peaked at 7 kilometers per year (4.3 miles per year) in late 2013, and slowed thereafter to a summertime peak of just 5 kilometers per year (3.1 miles per year) in 2017. At the same time, ocean temperatures in a deep bay near the glacier fjord entrance dropped dramatically, from 3.5 degrees Celsius (38.3 degrees Fahrenheit) to 1.5 degrees Celsius (34.7 degrees Fahrenheit) as a cool pulse of water displaced warmer water that had previously persisted in the area. The authors of the study pointed out that, while it may appear that ice loss from the ice sheet is slowing, their results merely show how critical the interaction is between deep glacier ice and warm ocean water, and that it is inevitable, given a generally warming ocean, that rapid ice loss will again occur. However, the slowdown of ice flow at Jakobshavn Isbrae (and for other glaciers) for the past two years may imply slowing of mass loss, which may persist for several more years.

Early warmth, early melting, and early darkening in western Greenland

Fig7_NUUK_PromiceData

Figure 7. The top graph shows weather and snow measurements for a site on the Greenland Ice Sheet east of the coastal city of Nuuk (NUUK_U, 72.39 degrees North, 27.26 degrees West, 988 meters or 3,240 feet elevation). The top graph illustrates how a drop in snow reflectance (albedo) coincided with early melting in May 2019, as air temperatures surged above freezing. Both graphs show the average conditions for albedo and air temperature for the preceding 11 years.

Credit: Jason Box, Programme for Monitoring of the Greenland Ice Sheet (POMICE)
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Low snowfall over western Greenland, combined with the early warming, has resulted in an early onset of the melt season at several automated weather stations (AWS) managed by Programme for Monitoring of the Greenland Ice Sheet (PROMICE), a Danish ice and climate research site. The stations have been maintained for the past 12 years, providing a record that permits comparison of 2019 to the recent past. Colleague Jason Box of the Danish Geological Survey produced these graphics and has also compiled a video on current conditions in Greenland and the likelihood of an extensive melt year in 2019.

Further reading

Khazendar, A., Fenty, I. G., Carroll, D., Gardner, A., Lee, C. M., Fukumori, I., … & Noël, B. P. 2019. Interruption of two decades of Jakobshavn Isbrae acceleration and thinning as regional ocean cools. Nature Geoscience,12; 277-283, doi:10.1038/s41561-019-0329-3.

The 2019 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