2016 Ice Sheet Assessment


Aaron Letterly
14 July 2017

Greenland Surface Melt


In 2016, the large ice sheet that covers over 80% of Greenland’s surface experienced above-average melting. From June through September, warmer-than-average temperatures coupled with more than 20 hours of daily sunlight led to an ice mass balance by mid-August that was -3909 Gt (gigatons) relative to April 2002 (Wiese et al. 2017). Snow and ice melt in Greenland’s coastal regions were particularly strong, and when Greenland’s summer albedo in 2016 was compared to the average summer albedo from 1982-2010, anomalies as high as -40% were commonplace. In the summer of 2016, early-season melt events in April and May decreased snow cover (NSIDC, 2016), particularly in the Southwestern and Northern regions of Greenland (Figure 1). As the affected coastal regions continued warming throughout the summer, albedo values plummeted far below their average.

Figure 1
Figure 1: Broadband albedo (reflectivity) anomaly over Greenland from June 2016 to September 2016 using the AVHRR Polar Pathfinder-Extended (APP-x) albedo data. Large decreases in albedo that lessen towards the interior of the ice sheet represent more exposed ice in the coastal regions and more interior melting than usual. The anomaly is relative to the 1982-2016 mean.
Figure 2a
Figure 2b
Figure 2: Surface temperature (left) and geopotential height anomaly (right) over Greenland form June 2016 to September 2016. Anomaly values are compared to mean values from 1982-2015 over the same months. Data are from NOAA/ESRL, Boulder, CO.

Ice Mass Variation Since 2002


NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites have provided data over the last 15 years showing that the ice sheets in both Greenland and Antarctica have decreased in mass. GRACE data have also shown an acceleration of land ice decrease (in both Greenland and Antarctica) since 2009. Figure 3 shows the time series of ice mass anomalies compared to the 2002-2016 average. Extreme melting at the edges of the Greenland Ice Sheet has outpaced the accumulation of ice at its center, resulting in immense losses in its total mass. The Antarctic Ice Sheet, however, covers such a large geographic area that unique melting conditions may occur simultaneously over different regions. West Antarctica and the Antarctic Peninsula have generally lost mass over the last 15 years, while ice mass has increased in Eastern Antarctica. Opposite regional trends in ice mass balance have slowed the rate of decrease of Antarctic ice mass, losing 125 (±39) gigatons per year, compared to Greenland’s yearly loss of 287 (±21) gigatons per year.

Figure 3
Figure 3: Anomaly in gigatons relative to the 2002-2016 mean for the Greenland Ice Sheet (cyan) and Antarctic Ice Sheet (magenta). Data are from GRACE.

References


NSIDC, 2016: 2016 melt season in review, National Snow and Ice Data Center, http://nsidc.org/greenland-today/category/analysis/, October 26, 2016.

Watkins, MM, DN Wiese, D-N Yuan, C Boening, and FW Landerer (2015), Improved methods for observing Earth's time variable mass distribution with GRACE using spherical cap mascons. J. Geophys. Res. Solid Earth, 120, 2648_2671. doi: 10.1002/2014JB011547.

Wiese, D. N., D.-N. Yuan, C. Boening, F. W. Landerer, and M. M. Watkins (2017) Antarctica Mass Variability Time Series Version 1 from JPL GRACE Mascon CRI Filtered

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