A melt spike in September?

As most of the western United States baked under a prolonged, record-setting heatwave at the beginning of September, Greenland also underwent a very unusual late-season melt event. Summit Station in Greenland, at an elevation of more than 3,200 meters (10,500 feet), surpassed the melting point for the first time on record in September on the afternoon of September 3. A strong high air pressure region parked at the southeastern edge of Greenland and drew warmer air northward along the western coast of Greenland and Baffin Bay beginning on September 2, leading to the melt event.

Overview of conditions

Figure 1. The top map shows the cumulative melt days for the 2018 melt season through July 7 (upper left) and the difference from the average (upper right) for May and June combined, referenced to the 1981 to 2010 period. Below is a plot of daily melt area for the 2018 season through July 7, compared with melt extents for 2017, 2016, and the 1981 to 2010 period. Data courtesy of Thomas Mote, University of Georgia. About the data Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia High-resolution image

Figure 1a. The top map shows the cumulative melt days for the 2022 melt season through September 5 (upper left) and the difference from the average (upper right) as referenced to the 1981 to 2010 period for the same time period. Below is a plot of daily melt area for the 2022 season through September 5. Data courtesy of Thomas Mote, University of Georgia. About the data

Credit: National Snow and Ice Data Center/Thomas Mote, University of Georgia
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Melt extent for September 2, 3, 4 and 5 showing the progression of the melt event across Greenland from passive microwave satellite observations. Credit: National Snow and Ice Data Center/T. Mote, University of Georgia High-resolution image

Figure 1b. These maps show the melt extent for September 2, 3, 4, and 5, illustrating the progression of the melt event across Greenland from passive microwave satellite observations. Data courtesy of Thomas Mote, University of Georgia. About the data

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

Unprecedented in the 44 years of continuous satellite monitoring, a late season heat wave and melt event occurred in Greenland from September 2 to 5. At the peak on September 3, more than one-third (36 percent) of the ice sheet, or around 600,000 square kilometers (232,000 square miles) had surface melting (Figure 1a). The only comparable event so late in the season was in 2003, in late August (in terms of melt area) when temperatures at Summit reached only -2.5 degrees Celsius (27.5 degrees Fahrenheit). The melt event began along the southwestern coast on September 2, and moved rapidly inland and northward on September 3, accompanied by heavy rainfall that enhanced melt at lower elevations, and enhanced snowfall at higher elevations (Figure 1b).

To date this year, Greenland has had a near-average melt year overall, with the total melt-day area ranking twentieth in the 44-year record (Figure 1a). Melting is slightly above average in both northeastern and south-central Greenland, and slightly below average along the southeast coast and northwest.

Conditions in context

 Figure 2. The top plot illustrates average surface air pressure in millibars for the period September 1 to 3 for Greenland and the surrounding areas. The H indicates the center of the strong high air pressure cell that generated the northward winds along the western Greenland coast and Baffin Bay. The bottom plot shows wind direction (white streamlines) and surface temperature (color) for Greenland and the surrounding region on September 3 at mid-day.||Credit:National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research)|High-resolution image

Figure 2a. The top plot illustrates average surface air pressure in millibars for the period September 1 to 3 for Greenland and the surrounding areas. The H indicates the center of the strong high air pressure cell that generated the northward winds along the western Greenland coast and Baffin Bay. The bottom plot shows wind direction (white streamlines) and surface temperature (color) for Greenland and the surrounding region on September 3 at mid-day.

Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research
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Figure 4. Preliminary temperature, dew point, and air pressure record from NSF’s Summit Station in Greenland, posted by NOAA at www.xxx.xxx for September 2-5, 2022. Note that these data were not accessible for several hours early on September 4th. Data courtesy of the National Oceanic and Atmospheric Administration Global Monitoring Laboratory. Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research); and www.nullschool.net High-resolution image

Figure 2b. Preliminary temperature, dew point, and air pressure record from National Science Foundation’s Summit Station in Greenland, posted by the National Oceanic and Atmospheric Administration (NOAA) for September 2 to 5, 2022. Note that these data were not accessible for several hours early on September 4. Data courtesy of the National Oceanic and Atmospheric Administration Global Monitoring Laboratory.

Credit: Christopher A. Shuman, University of Maryland Baltimore County at NASA Goddard Space Flight Center
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Warm air moved rapidly northward from the central North Atlantic Ocean. A strong and relatively slow-moving high-pressure region and an atmospheric river—a relatively narrow band of high-moisture air—brought a considerable volume of snow and rain in the early days of the event (Figure 2a). This pulse of warm air then flowed eastward over the top of the ice sheet and descended onto the eastern edge, extending melting to the northern and eastern coast on September 4 and 5.

Temperatures at Summit Station were low in the early morning hours of September 2, but rose rapidly during that day. Increasing air pressure, which often accompanies melt events at Summit, began on September 3 and continued high through much of September 4. On September 3, several hours of above-freezing temperatures were recorded, reaching a peak of 0.4 degrees Celsius (32.7 degrees Fahrenheit) around 15:00 Greenwich Mean Time (GMT) on the third (Figure 2b). High temperatures on September 4 were slightly above -2 degrees Celsius (28.4 degrees Fahrenheit) and similarly warm conditions continued across the island until September 6.

The big runoff

This graph shows Greenland’s melt runoff (top graph) and the total melt in billions of tons (bottom graph) for each day since June 1 to July 25, for several time-periods. Melt runoff is the amount of meltwater that reaches the ocean; total melt amount is larger, because for some of the higher-elevation melting, the meltwater soaks into the snow and re-freezes. Credit: MARv3.12, X. Fettweis, University of Liège, Belgium High-resolution image

Figure 3. This graph shows Greenland’s melt runoff and the total melt in billions of tons from Jun 1 to September 5, 2022. Melt runoff is the amount of meltwater that reaches the ocean.

Credit: MARv3.14, Xavier Fettweis, University of Liège, Belgium
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Meltwater runoff, or the amount of surface water entering the ocean, from the Greenland Ice Sheet began increasing on September 2 at 5.6 billion tons per day, and peaked at just under 12 billion tons per day on the September 3. Data are from the Regional Atmosphere Model (MAR), which is a reanalysis model that uses Global Forecast System data from the National Centers for Environmental Prediction (NCEP). On September 4 and 5, runoff continued at 7.7 and 6.6 billion tons, respectively. The runoff total for September 3 was the highest of this melting season and is one of the 10 highest runoff days since 1950. However, this was moderated partially by heavy rainfall and snowfall on September 2 and 3, totaling 15.6 billion tons of input.

Such an intense melt and runoff event at this time of the year is exceptional as the energy coming from solar radiation is already very low at the beginning of September. Most of the record high runoff events have occurred in July, such as in 2012 and 2019.

This event has been followed by colder conditions, which caused refreezing of the melt at the top of the snowpack. This will lead to widespread formation of ice lenses within the snowpack. These shallow and impermeable ice lenses will reduce the capacity of the snowpack to retain meltwater next summer, tending instead to promote more widespread runoff and less local refreezing (MacFerrin et al., 2021).

Being there

Figure 4. Figure 6. Top, a picture from southern Greenland (north of Qagssimiut near the southern tip of the ice sheet) on September 2. Ominous skies with newly-defined Asperitus clouds indicative of intense weather. Bare dirty ice was present everywhere, and run-off and rain-driven flooding resumed after a late August hiatus. Bottom, wavy structure in the lower cloud deck indicative of asperitus clouds. Photos by Mette Hansgaard

Figure 4. The top photograph was taken in southern Greenland (north of Qagssimiut near the southern tip of the ice sheet) on September 2. Skies with newly-defined asperitas clouds are indicative of intense weather. Bare dirty ice was present everywhere, and runoff and rain-driven flooding resumed after a late August hiatus. The bottom photograph shows a wavy structure in the lower cloud deck indicative of asperitas clouds.

Credit: Mette Hansgaard
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A group of researchers camped near the ice edge in southern Greenland when the melt event began on September 2. The group observed intermittent rain, warm winds, and unusual wave-like clouds indicative of unstable conditions.

References

MacFerrin, M., H. Machguth, D. v. As et al. 2019. Rapid expansion of Greenland’s low-permeability ice slabs. Nature 573, 403–407. doi:10.1038/s41586-019-1550-3

Heat ripple

A moderate melt surge swept across northern Greenland and then encompassed much of the ice sheet perimeter in mid-July. Overall, the 2022 summer season in Greenland continues at a modest pace relative to the past few years (notably 2021 and 2019) as a result of neutral North Atlantic Oscillation (NAO) index conditions promoting frequent northern winds over Greenland but exceptional melt and southerly winds over Svalbard, the Norwegian-owned islands northeast of Greenland.

Overview of conditions

Figure 1. The top left map shows cumulative melt days on the Greenland Ice Sheet for the spring 2022 melt season. The top right map shows the difference from the 1981 to 2010 average melt days for the same period. The bottom graph shows daily melt area for Greenland from May 25 through August 6, 2022, with daily melt area for the preceding three years. The grey lines and bands depict 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 shows cumulative melt days on the Greenland Ice Sheet for the spring 2022 melt season. The top right map shows the difference from the 1981 to 2010 average melt days for the same period. The bottom graph illustrates daily melt area for Greenland from May 25 through August 6, 2022, with daily melt area for the preceding three years. The grey lines and bands depict 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

As of July 25, 2022, the Greenland Ice Sheet seasonal melting cumulative extent (the sum of each day’s melt area since April 1) was 14.00 million square kilometers (5.41 million square miles), ranking it nineteenth highest in the 44-year satellite record. A slow start in April, May, and June preceded slightly above-average melt extents in July, culminating in a moderately extensive surge in melt across northern Greenland on July 15 to 18, and more widespread coastal melting in the days following through July 25. The events led to a brief period of relatively high meltwater run off, bringing the net snowfall and surface melt mass change to near the 1981 to 2010 average.

Melting from April 1 to July 25 has been slightly above the 1981 to 2010 mean along the southwestern coast, often the area with the greatest number of melt days, and above average across the northern ice sheet, the site of the first part of the recent surge in melt area. Areas of below-average melting along the southeast coast and parts of the northwest offset this. Overall, the melt day count is near-average for this date.

Conditions in context

Figure 2. The top plot shows average air temperature as a difference from the 1991 to 2020 average at the 700 millibar level, at about 3,000 meters (10,000 feet) above sea level, from June 20 to July 25, 2022. The bottom plot shows height of the 700-millibar pressure level as a difference from its average height over the same period.||Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research). |High-resolution image

Figure 2. The top plot shows average air temperature as a difference from the 1991 to 2020 average at the 700 millibar level, at about 3,000 meters (10,000 feet) above sea level, from June 20 to July 25, 2022. The bottom plot shows height of the 700-millibar pressure level as a difference from its average height over the same period.

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

Air temperatures at the 700 millibar level (about 3,000 meters or 10,000 feet of elevation) for June 20 to July 25 were generally near-average, with somewhat warmer-than-average conditions along the northern and southern ends of the islands. Average temperatures were 2 degrees Celsius (4 degrees Fahrenheit) above average near Thule in northwest Greenland, and about 1 degree Celsius (2 degrees Fahrenheit) above average near Nuuk, the capital of Kalaalit Nunaat (the nation of Greenland). Near the National Science Foundation’s Summit Station, temperatures were near average through this period, although the station experienced several above average days during the more extensive melt events in the third week of July.

The pressure pattern (indicated by the height of the 700 millibar pressure level) shows a stronger-than-average low pressure area off the eastern coast of the island, and high pressure along the southern tip, which tended to drive warm winds across the southern tip and northward along Baffin Bay’s eastern coast. However, the pattern in the north favors more frequent, cooler, northerly or northeasterly winds, pushing this 2022 melt season towards average or below-average intensity.

Heat ripple

Figure 3a. This graph shows Greenland’s melt runoff (top graph) and the total melt in billions of tons (bottom graph) for each day since June 1 to July 25, for several time-periods. Melt runoff is the amount of meltwater that reaches the ocean; total melt amount is larger, because for some of the higher-elevation melting, the meltwater soaks into the snow and re-freezes. ||Credit: MARv3.12, X. Fettweis, University of Liège, Belgium |High-resolution image

Figure 3a. This graph shows Greenland’s melt runoff (top graph) and the total melt in billions of tons (bottom graph) for each day since June 1 to July 25, for several time-periods. Melt runoff is the amount of meltwater that reaches the ocean; total melt amount is larger, because for some of the higher-elevation melting, the meltwater soaks into the snow and re-freezes.

Credit: MARv3.12, X. Fettweis, University of Liège, Belgium
High-resolution image

Figure 3b. This plot shows preliminary air temperature, dew point, and air pressure readings from Summit, Greenland, for late July 21 through early July 24. ||Credit: XX |High-resolution image

Figure 3b. This plot shows preliminary air temperature, dew point, and air pressure readings from Summit, Greenland, for late July 21 through early July 24. Data courtesy of the National Oceanic and Atmospheric Administration Global Monitoring Laboratory.

Credit: Christopher A. Shuman, University of Maryland Baltimore County at NASA Goddard Space Flight Center
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Figure 3c. This animation shows temperature difference from average (in color, scale is in degrees Celsius) and winds (arrows on the plot) at the 700 mbar level, spanning July 10 to July 25, 2022. The animation shows the progression of two warm pulses of air: one coming up and over Scandinavia, leading to the melting seen on July 16 through 18 in far northern Greenland, and one moving up through Baffin Bay, initiating the second pulse of melting seen on July 20 through 24, with warm conditions reaching the Summit Station. Note the warm conditions over Svalbard on July 17th.||Credit: Xavier Fettweis, University of Liege, Belgium, and NOAA|High-resolution image

Figure 3c. This animation shows temperature difference from average (in color, scale is in degrees Celsius) and winds (arrows on the plot) at the 700 mbar level, spanning July 10 to July 25, 2022. The animation shows the progression of two warm pulses of air: one coming up and over Scandinavia, leading to the melting seen on July 16 through 18 in far northern Greenland, and one moving up through Baffin Bay, initiating the second pulse of melting seen on July 20 through 24, with warm conditions reaching the Summit Station. Note the warm conditions over Svalbard on July 17.

Credit: Xavier Fettweis, University of Liege, Belgium, and National Oceanic and Atmospheric Administration
High-resolution image

Beginning on July 15, a strong ridge of high pressure began to develop over Greenland, and warm air moving in from both the Canadian Arctic along West Greenland and from Svalbard to the east initiated an extensive melt event across northern Greenland after having generated the highest recorded melt volume over Svalbard on July 17.  Models of the initial event, spanning July 16 to 18, showed that meltwater runoff amounts increased to about 6 billion tons per day, or about 35 percent more than average at this time of summer (Figure 3a). As noted in media coverage, temperatures were near 15 degrees Celsius (about 60 degrees Fahrenheit) in the Thule area. Then in the following days, a pulse of warm air moved northward along the western coast, extending the melt area and intensity further, with melt runoff reaching 10 billion tons per day on July 22. During this second modest warm event, temperatures reached within 3 degrees Celsius (5 degrees Fahrenheit) of the melting point at Summit Station, about 8 degrees Celsius (14 degrees Fahrenheit) above average (Figure 3b). Melt extent and melt runoff returned to near-average levels after July 25.

An animation of air temperature differences from average and wind patterns (Figure 3c; click to animate) shows the progression of two warm pulses of air from July 10 to July 25: one northward over Scandinavia, promoting melting across northern Greenland seen on July 16 to 18, and one moving northward through Baffin Bay, initiating the second pulse of melting on July 20 to 24, with warm conditions reaching  Summit Station, central Greenland. Note the extremely warm conditions over Svalbard on July 17.

Greenland’s reflectivity

Figure 4a. This map shows the difference from average reflectivity, or average albedo, for the Greenland Ice Sheet from July 16 to 24, relative to the same period for the 2017 to 2021 average. Red areas in the north and northwest of the island indicate the extensive snow darkening or exposure of bare ice during the strong melt events of July. Areas along the southwestern coast in dark blue along the western coast indicate brighter than average snow conditions due to below-average melt. ||Credit: Jason Box, Geological Survey of Denmark and Greenland (GEUS) and Adrien Wehrlé, University of Zurich |High-resolution image

Figure 4a. This map shows the difference from average reflectivity, or average albedo, for the Greenland Ice Sheet from July 16 to 24, relative to the same period for the 2017 to 2021 average. Red areas in the north and northwest of the island indicate the extensive snow darkening or exposure of bare ice during the strong melt events of July. Areas along the southwestern coast in dark blue along the western coast indicate brighter than average snow conditions due to below-average melt.

Credit: Jason Box, Geological Survey of Denmark and Greenland (GEUS) and Adrien Wehrlé, University of Zurich
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Figure 4b. This chart illustrates the variation in reflectivity, not the difference from average, for northern Greenland as it varies with elevation for the periods before (July 5 to 9) and after the strong melt event in northern Greenland (July 15 to 19). ||Credit: Jason Box, Geological Survey of Denmark and Greenland (GEUS) and Adrien Wehrlé, University of Zurich. |High-resolution image

Figure 4b. This chart illustrates the variation in reflectivity, not the difference from average, for northern Greenland as it varies with elevation for the periods before (July 5 to 9) and after the strong melt event in northern Greenland (July 15 to 19).

Credit: Jason Box, Geological Survey of Denmark and Greenland (GEUS) and Adrien Wehrlé, University of Zurich
High-resolution image

Greenland’s snow and ice reflectivity, known as albedo, responds to warming events in several ways that all tend to make the surface darker, and therefore more absorbing of solar energy, which is abundant across northern Greenland at this time of year. During the mid-July melt event in northern Greenland the northern portion of the ice sheet reflected 5 to 10 percent less sunlight as a result of coarsening snow grains, wet conditions in the snow, or greater exposure of darker bare ice (Figure 4a). These factors mean that ice sheets under warming climate conditions undergo an amplification of absorbing energy as the snow warms and melts because of high amounts of sunlight, darkening snow and ice surfaces, and meltwater running off the ice sheet.

Greenland’s reflectivity can now be tracked on a daily basis (if clouds permit) at a resolution of 300 meters (about 1,000 feet) using the European Space Agency’s Sentinel-3 satellite’s Ocean and Land Color Instrument (Figure 4b). This product is now available from the Geological Survey of Denmark and Greenland (GEUS). Albedo controls the amount of solar energy that the snow and ice surface absorbs during daylight hours, and is strongly influenced by the buildup of dust, soot, and ice algae on the surface.

Severe summer in Svalbard

Figure 7. The top plot shows net gain or loss of ice for the glaciers and ice caps of Svalbard (also known as Spitzbergen) for the current hydrologic year through July 25. The bottom figure shows surface air temperature difference from average for May 1 to July 25, 2022, for the far northern Atlantic and the Svalbard region. ||Credit: X. Fettweis and MAR 3.12, University of Liege, Belgium; and NOAA NCEP |High-resolution image

Figure 5. The top plot shows net gain or loss of ice for the glaciers and ice caps of Svalbard (also known as Spitzbergen) for the current hydrologic year through July 25. The bottom figure shows surface air temperature difference from average for May 1 to July 25, 2022, for the far northern Atlantic and the Svalbard region.

Credit: X. Fettweis and MAR 3.12, University of Liege, Belgium; and the National Oceanic and Atmospheric Administration National Centers for Environmental Prediction
High-resolution image

The current cumulated melt over Svalbard, from June 1 to July 31, is 1.5 times larger than the previous record from 2018, an event having a 1 in 3.5 million chance (a ‘5 sigma deviation from the mean’) if climate were completely random. However, under the current global warming trend driven by heat-trapping gases, these astronomical odds are much lower. The causes of the extreme summer are linked to several recent events. Winter snowfall was low, allowing older, darker snow or old, bare ice to make an earlier appearance during the melt season. The sea ice moved north of the archipelago at the end of spring, something that does not always happen even by late summer. This exposed the ocean during the peak sunshine period, and allowed warm air to reach the islands without flowing over a frozen ocean surface first. Ocean conditions are also very warm near Svalbard as a result. Lastly, the wind and air pressure patterns have been very persistent for the region this summer, setting up persistent southerly warm winds reaching the archipelago but bringing northern winds to Greenland frequently, explaining why melt is close to average over Greenland and exceptional over Svalbard.