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Sudden shift to southern heat

Late June ushered in a significant shift in weather and melting for Greenland, particularly for the southern portion of the ice sheet, known as South Dome, where melting is currently on a record pace. Melting along the northern rim of the ice sheet is also greater than average. These changes are a result of a shift in the air circulation, associated to negative North Atlantic Oscillation (NAO) index values. High air pressure now covers the island, bringing warm winds from the southwest and favoring sunnier condition enhancing the surface melt in the ablation zone, for which the extent is now close to the previous records in the summers of 2012 and 2019.

Overview of conditions

Beginning around June 23, the areal extent of Greenland’s surface melting and runoff increased significantly. Several widespread melting events covering about 800,000 square kilometers (302,000 square miles) or up to 50 percent of the ice sheet occurred on June 27, July 6 to 7, and July 11, as several pulses of warm air swept across the southern portion of the ice sheet and northward around the northern coast. The total number of days with melting are now well above average throughout the southern and southwestern portions of the ice sheet by up to 5 to 15 days, and along its northern flank by about 10 days. Total melt-day extent, the sum of daily melt extents for the season so far, is now sixth highest overall. Melt-day extent over the southern portion of the ice sheet is now at a record high for the 45-year satellite record. A significant increase in the estimated (modelled) run-off has occurred in the South Dome and Zachariæ Isstrøm Glacier regions, exacerbated by the below-average net accumulation in the southern and northeastern portions of the ice sheet at the end of spring. Moreover, at least some melting has now occurred over most of the ice sheet, even at high elevations, and this preconditions the snow for further melting by warming and darkening the upper layers. We have in part corrected the parameters for determining melt from the satellite data by adjusting the baseline reference period used to characterize the pre-melting springtime snowpack. However, somewhat unusual conditions in the upper Jakobshavn Gletscher region, inferred to be due to a heavy surface frost event sometime earlier in the spring, prevent a complete removal of the anomalous early-melt area. This remaining possible inaccuracy is now a small fraction of the total melt-day mapping for the year (less than 5 percent).

The top left map illustrates cumulative melt days on the Greenland Ice Sheet for the 2023 melt season through July 12. The top right map illustrates the difference from the 1981 to 2010 average melt days for the same period. The bottom graph shows the daily melt area for Greenland from April 1st through August 6th for 2023 and several of the near-record melt years in this century. The gray lines and bands depict the average daily melt area for 1981 to 2010, the interquartile range, and the interdecile range
Figure 1. The top left map illustrates cumulative melt days on the Greenland Ice Sheet for the 2023 melt season through July 12. The top right map illustrates the difference from the 1981 to 2010 average melt days for the same period. The bottom graph shows the daily melt area for Greenland from April 1st through August 6th for 2023 and several of the near-record melt years in this century. The gray lines and bands depict the average daily melt area for 1981 to 2010, the interquartile range, and the interdecile range. — Credit: National Snow and Ice Data Center/T. Mote, University of Georgia

Conditions in context

Air temperatures across Greenland have been above average over the past several weeks, by up to 1.5 to 2 degrees Celsius (3 to 4 degrees Fahrenheit) in the south and over 3 degrees Celsius (5 degrees Fahrenheit) in the north-central area. Air pressure patterns have changed markedly since the May-June period, with higher-than-average pressure both to the southwest and the northeast of the island. This pattern has brought a series of warm air pulses across the island from the southwest. Both melt volume and surface meltwater run-off have increased since the weather pattern change. Daily estimated totals of melt have been about 15 billion tons per day for the first half of July, and estimated melt run-off about 10 billion tons per day. These anomalies have been two standard deviations above average since the end of June. Negative NAO conditions are expected to continue through the end of July, and we expect the total July runoff at South Dome to exceed the previous record years of 2002, 2007, 2012, and 2019. Given the below-average snowfall in the southern and northeastern areas, and the frequent occurrence of rainfall this July, the surface is pre-conditioned for further melting, exposing more ice-covered ablation areas especially near the coast. Further melting in July and early August will be enhanced by sunnier conditions as a result of negative NAO condition and will lead to high melt run-off.

The above plot illustrates average surface air temperature as a difference from the 1991 to 2020 mean for the period of June 21 to July 12, 2023, for Greenland and the surrounding areas. Warmer-than-average conditions are now present across nearly all of the ice sheet.
Figure 2a. The above plot illustrates average surface air temperature as a difference from the 1991 to 2020 mean for the period of June 21 to July 12, 2023, for Greenland and the surrounding areas. Warmer-than-average conditions are now present across nearly all of the ice sheet. — Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data
Figure 2b. This plot shows the difference from average of the height of the 700-millibar level (about 3 kilometers or 10,000 feet above sea level), an indication of the mean air pressure, for Greenland and the surrounding areas for June 21 to July 12. High pressure to the southwest of Greenland drove warm air along the western coast and across the ice sheet.
Figure 2b. This plot shows the difference from average of the height of the 700-millibar level (about 3 kilometers or 10,000 feet above sea level), an indication of the mean air pressure, for Greenland and the surrounding areas for June 21 to July 12. High pressure to the southwest of Greenland drove warm air along the western coast and across the ice sheet. — Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data
The top graph shows melt run-off and the bottom graph shows daily surface melt total from the Modèle Atmosphérique Régional (MAR) model for May 1 through July 18. The last few days are based on a forecast.
Figure 3. The top graph shows melt run-off and the bottom graph shows daily surface melt total from the Modèle Atmosphérique Régional (MAR) model for May 1 through July 18. The last few days are based on a forecast. — Credit: X. Fettweis, University of Liège and MAR3.12

Record pace of melting at South Dome

Warm conditions in both the northern and southern sections of the island have led to a record high melt-degree-day index for weather stations in those areas for the periods when they have operated. For all days in a season where the maximum temperature is above freezing, the melting degree day index sums the total number of degrees above freezing for each day. At both the Northeast Eemian automatic weather station (NEM) and the South Dome automatic weather station (SDM), the total melting degree day index is ahead of the past record melt season, 2012 (Figure 4). At South Dome, an extended period of above-freezing temperatures occurred from July 6 to 12, pushing its total melting degree-days index rapidly higher (Figure 5). However, both 2019 and 2012 had very intense melting in the second half of July and in early August. At Summit Station, we have been monitoring the reported air temperature, and on several occasions in June and into July the air temperatures have been very close to or slightly exceeding the melting point. The above freezing temperatures on June 26 (Figure 6) represents a record warm air temperature for June at Summit.

Figure 4. At top left, melting degree days total for 2023 up to July 14 for 2006 through 2023 for the Northeast Eemian (NEM) automatic weather station (AWS) site; at top left melting degree days up to July 14 for 1996 through 2023 for South Dome (SDM) AWS. Melting degree days are the sum of the number of degrees above melting at the peak daily temperature for days with melt in a summer season. The bottom graph is a plot of hourly air temperature for the SDM AWS for 2023 showing the persistent period of melt
Figure 4. At top left, melting degree days total for 2023 up to July 14 for 2006 through 2023 for the Northeast Eemian (NEM) automatic weather station (AWS) site; at top left melting degree days up to July 14 for 1996 through 2023 for South Dome (SDM) AWS. Melting degree days are the sum of the number of degrees above melting at the peak daily temperature for days with melt in a summer season. The bottom graph is a plot of hourly air temperature for the SDM AWS for 2023 showing the persistent period of melting during July 6 to 12. — Credit: J. Box and the Geological Survey of Denmark and Greenland (GEUS), PromIce GC-Net
This graph shows surface mass balance, the sum of snow and rainfall minus evaporation and run-off, difference from the 1981 to 2010 average for the South Dome area for the 2022 to 2023 hydrological year and several recent years through mid-July.
Figure 5. This graph shows surface mass balance, the sum of snow and rainfall minus evaporation and run-off, difference from the 1981 to 2010 average for the South Dome area for the 2022 to 2023 hydrological year and several recent years through mid-July. — Credit: J. Box and the Geological Survey of Denmark and Greenland (GEUS), PromIce GC-Net
Figure 6. National Oceanic and Atmospheric Administration Global Monitoring Laboratory temperature data from the Summit Observatory, initially transmitted at 1-minute average resolution, are plotted here at 10-minute averages for the month of June (late June 2008 through 2023). The previous record high temperature for June was on June 12, 2019, briefly at 0.1 degrees Celsius (32 degrees Fahrenheit). On June 26, 2023, a temperature of 0.4 degrees Celsius (33 degrees Fahrenheit) was seen during a several-hour
Figure 6. National Oceanic and Atmospheric Administration Global Monitoring Laboratory temperature data from the Summit Observatory, initially transmitted at 1-minute average resolution, are plotted here at 10-minute averages for the month of June (late June 2008 through 2023). The previous record high temperature for June was on June 12, 2019, briefly at 0.1 degrees Celsius (32 degrees Fahrenheit). On June 26, 2023, a temperature of 0.4 degrees Celsius (33 degrees Fahrenheit) was seen during a several-hour stretch of near or above freezing conditions at the Summit weather station. — Credit: Christopher A. Shuman, University of Maryland, Baltimore County at NASA Goddard Space Flight Center and Michael Schnaubelt, Johns Hopkins University, using data from NOAA’s Global Monitoring Laboratory

Greenland catches the wave

Air circulation in the Arctic is dominated by westerly winds that encircle the Pole, driven at a fundamental level by the difference in temperature between the tropics and the high latitudes. The boundary of these eastward-flowing winds is marked by the polar jet stream. As Arctic and Greenland air temperatures have warmed, with strongly decreased sea ice and springtime snow cover and increased surface melting, the notion has been forwarded that the jet stream could become more sinuous, or ‘wavier’, leading to weather extremes of persistent warmer or cooler than average conditions. This is one of the more debated potential aspects of Arctic Amplification, that is, the processes that seem to amplify the pace of warming in the high northern latitudes. A new study supports this hypothesis based on the observed summertime waviness of the airflow over northern Canada, Greenland, and the North Atlantic for 1979 through 2022. During the months of June, July, and August there has been a small but statistically significant increase in the waviness of air circulation in the region of Greenland. Since the mid-2000s, waviness of the airflow has increased in concert with a strong decrease in the June snow cover for North America and Europe. Moreover, this is associated with high pressure over Greenland, creating a ‘blocking high’ that can remain fixed for extended periods (weeks to months). High pressure conditions in Greenland are associated with increased warmth and melting and increased solar energy input to the ice sheet. Given the low June snow cover for 2023, and the emergence of above average pressure over Greenland in June and the first half of July, there is a strong possibility that this pattern will persist through this year as well.
 

Figure 7. This figure shows example days of the mapping of air-flow waviness over the study area used in the Preece et al., 2023 study. The top map shows airflow contours with low sinuosity (waviness) on August 16, 2001. The bottom map shows a strong waviness pattern on July 11, 2012.
Figure 7. This figure shows example days of the mapping of air-flow waviness over the study area used in the Preece et al., 2023 study. The top map shows airflow contours with low sinuosity (waviness) on August 16, 2001. The bottom map shows a strong waviness pattern on July 11, 2012. — Credit: Modified from Preece et al., 2023, Nature Communications

Ice Art

On June 26, photographer and explorer Sebastian Copeland captured this image of an ice cliff during the widespread melting event at that time.

Melting ice and ice mélange near Qaanaaq, Greenland.
Melting ice and ice mélange near Qaanaaq, Greenland. — Credit: Sebastian Copeland

Further reading

Preece, J. R., T. L. Mote, J. Cohen, L. J. Wachowicz, J. A. Knox, M. Tedesco and G. J. Kooperman. 2023. Summer atmospheric circulation over Greenland in response to Arctic amplification and diminished spring snow cover. Nature Communications, 14(1), 3759. doi:10.1038/s41467-023-39466-6