Ice Sheet Analysis

A record melt event in mid-June

MONDAY, JULY 1, 2019

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: Melt maps and graph — 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. — Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia

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: Temperature and pressure maps — 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

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

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

Figure 3: Maps and satellite image — 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

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: Temperature graph — 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)

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: Mel graphs — 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

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).