Greenland Climate
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The margin of the Greenland ice sheet moves back and forth depending on the climate. During cold times, like the ice ages, the ice margin advances and covers the land and may even form ice shelves extending into the ocean. In a warming climate, the ice margin retreats, revealing freshly exposed land.

The most sensitive part of the ice sheet margin is the outlet glaciers extending into the deep fjords. These may respond on an annual basis to changes in ocean temperature and circulation. When warm ocean water reaches the fjords and get in direct connection with the outlet glacier tongue, rapid changes may occur as has been seen for a large number of outlet glaciers in Greenland over the last decade.

The ice margin terminating on land responds more slowly to climate change, but is an area of considerable interest to the Greenland society. This part of the ice margin is utilized for generating hydro-electric power and also covers mineral deposits or poses challenges to neighbouring natural resource exploration. For these activities, local glaciers and ice caps separated from the ice sheet proper are just as relevant.

Monitoring the retreat of the ice margin requires knowledge of where the ice margin is in the first place. This was not well-defined at the onset of PROMICE and consequently, an effort was initiated to produce a map of all the Greenland ice masses, including both the ice sheet and the localized ice masses surrounding it, based on aerophotogrammetic surveys conducted 1978-1987 (see Figure 1). Airborne surveys are more detailed than satellite images and given the necessary attention, the error in determining the margin position is less than 10 metres.

The PROMICE map was recently published and the result can be seen in Figure 2. The total glacierized area including the ice sheet and all local glaciers and ice caps was calculated to be 1,804,638 ± 2,178 km2 (Citterio & Ahlstrøm, 2013). Of this area, 1,716,555 ± 947 km2 was the Greenland ice sheet and 88,083 ± 1,240 km2 consisted of local glaciers and ice caps.

As each major region in Greenland was surveyed in different years, the resulting map is only strictly synchronous within each large sub-region as shown in Figure 1. Yet, the PROMICE map has already been used for area change assessment yielding a loss of 2560 ± 260 km2 between the mid 1980s and 2011 (Kargel et al., 2012).

This number was obtained by updating the PROMICE map to summer 2011 using NASA LANCE Rapid Response MODIS imagery at 128 sites, while excluding known glacier surges. The observed area shrinkage from this analysis was c. 92 km2 per year from the 1980s to 2011.

This estimate is lower than recent estimates focused on outlet glacier fluctuations over the last decade, partly because outlet glaciers changed more slowly prior to the last decade and partly because land-terminating parts of the ice margin reacts more slowly to climate change.

An ice mask based on the PROMICE map is available here

Figure 1. Overview showing the margins of all ice masses in the PROMICE map, colour coded according to the data sources used to produce it (see Citterio & Ahlstrøm, 2013, for details). The actual year and geographic coverage of each flight campaign is shown.

Figure 2. Small-scale overview of the PROMICE aerophotogrammetric map of Greenland ice masses, colour coded according to our classification of ‘disconnected ice mass’, ‘local ice mass’ and ‘ice sheet’ (Citterio & Ahlstrøm, 2013).