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The 2024 melt season for the Greenland Ice Sheet is above the 1991 to 2020 average, but the total number of melt days and peak melt area for Greenland are within the midrange of the last 24 years. While snowfall in June and July covered dark bare ice areas on the ice sheet's margins, a heat wave in early July exposed this ice in western Greenland, increasing melt in that region. Temperatures so far this summer have been near the 1991 to 2021 average.
Overview of conditions
The ice sheet's melt through July was a tale of two coasts. The western ice sheet, where melting is often most intense, had below-average melt as of the end of July (Figure 1a). Along the entire eastern ice sheet, above average melt days were observed, although bare ice and melt runoff have not been common there. Since the end of July there has been an increase in melting along the western ice sheet margin and in far northeastern Greenland, with some melting reaching elevations above 1,700 meters (5,600 feet) in the southwest side (Figure 1b).
Figure 1a. The left map illustrates the cumulative melt days on the Greenland Ice Sheet for the 2024 melt season through July 31. The map on the right illustrates the difference from the 1981 to 2010 average melt days for the same period. The graph shows daily melt area from April 1 to July 31, 2024, with daily melt area for other high melt years, plus the record high year of 2012. The thick gray line depicts the average daily melt area for 1981 to 2010.— Credit:National Snow and Ice Data Center/T. Mote, University of Georgia
Figure 1b. The plot shows air temperatures from an automated weather station (known as KAN_U) operating in west-central Greenland, reporting multiple days of above-freezing conditions in early August. The map on the right shows the location of the weather station, which sits at 1,839 meters (6,033 feet).— Credit:J. Box, Geological Survey of Denmark and Greenland (GEUS)
Conditions in context
Air temperatures have been within 1 degree Celsius (2 degrees Fahrenheit) above and below the long-term average over most of Greenland in July (Figure 2a). Cooler conditions occurred across the south, while a small region in the north experienced warmer conditions. West of Greenland, a large area, covering western Baffin Bay and Baffin Island, had temperatures as low as 4 degrees Celsius (7 degrees Fahrenheit) below average.
The surface mass balance (SMB), or the total amount of snow and rain minus evaporation and run-off, was slightly above average for the season so far, a result of numerous late spring and summer snowfalls and modest melting (Figure 2b). Since the most active part of the melt season has passed, this year Greenland will likely have a net positive accumulation of snowfall. However, ice flow off the ice sheet continues to move at a fast rate, resulting in a net loss of its mass balance, as it has done since the early 2000s.
Figure 2a. These plots show weather conditions for the Greenland Ice Sheet for July 2024. The left panel shows air temperature as a difference from the 1991 to 2020 average in degrees Celsius. The right panel shows the height of the 700 millibar level at roughly 3,000 meters (10,000 feet) above sea level as difference from the 1991 to 2020 average.— Credit:National Centers for Environmental Prediction (NCEP) Reanalysis data
Figure 2b. The left map shows cumulative total surface mass balance, essentially snowfall minus meltwater run-off, for the Greenland Ice Sheet between September 1, 2023, and August 11, 2024, shown as millimeters of water equivalent on the surface. The map on the right shows the difference from average of the surface mass balance for the 1981 to 2010 reference period. Ten millimeters is about 0.4 inches.— Credit:X. Fettweis, University of Liège, MARv3.14
July warmth clears the snow, lets the water flow
As noted in the June posting, frequent spring snowfall added plenty of reflective snow cover on the west-central ice sheet, inhibiting melt and meltwater run-off (Figure 3a). Late snowfall delayed exposure of this bare ice. Two heatwaves in July increased snowmelt that uncovered the darker glacial ice, increasing melt and run-off locally as depicted in two Landsat satellite images (Figure 3b).
Figure 3a. The map on the left shows the albedo or reflectivity of the Greenland Ice Sheet as a difference from the 2017 to 2023 average on August 4, 2024. Blue areas are brighter than the long-term average, red areas are darker. The graph on the right shows the reflectivity of the spring and summer seasons for 2018 in purple, 2019 in red, and 2024 in blue, along with the long-term average as a black line and the typical range of values for each date as a gray band.— Credit:J. Box, Geological Survey of Denmark and Greenland (GEUS)
Figure 3b. These Landsat satellite images show the western edge of the Greenland Ice Sheet on June 28 (left) and July 22 (right). As summer melting progresses, the loss of white snow cover exposes the dark dust-laden ice. Ice front changes are also visible in the lower Sermeq Kujalleq, also known as Jakobshavn Glacier. These two views cover an area of about 99 x 96 kilometers (62 x 60 miles).— Credit:C. Shuman, University of Maryland, Baltimore County (UMBC) at NASA Goddard Space Flight Center (GSFC); data are from US Geological Survey (USGS)
