Contributions to Sea Level Rise: Antarctic Ice Sheet

The Antarctic Ice Sheet is by far the largest body of ice in the world, and therefore has the potential to cause massive SLR. However during the 20^th Century its contribution to SLR has been fairly limited considering its massive volume. This is due to Antarctica having not experienced significant temperature rise due to its isolation by the massive and cold Southern Ocean.

The volume of ice in Antarctica is equivalent to 60 m of SLR

Map of Antarctica, including major bases and ice shelves. Source

Current Situation

Antarctica is separated into two major ice sheets by the Transantarctic Mountains; the East and West Antarctic Ice Sheets. Overall there has been negligible thinning over the majority of the Ice Sheet in recent years explaining the limited contribution to SLR. Recent suggestions are that in terms of SLR the West Antarctic (~7 m SL equivalent) is most likely to lead to a large contribution as there has been evidence of increased ice stream velocity and ice loss in recent years. This is most often seen on floating ice shelves in West Antarctica. This is also shown by the thinning in the West Antarctic Ice sheet as shown by Chen et al., (2009).

Accelerated thinning in West Antarctica. Source

In addition catastrophic events of ice shelf collapse have been seen on the Antarctic Peninsula. The Larsen B Ice Shelf (3,250 km2) collapsed in 2002 due to warming of the Peninsula and meltwater ponding. Following that there was significant glacier speed up and thinning (Rignot et al., 2004). This suggests a possible acceleration in SLR if large parts of the many Antarctic ice shelves collapse. 

Location of major ice shelves (left) Catastrophic collapse of Larsen B Ice Shelf (right). Source

The Pine Island Glacier in West Antarctica is second in speed to Jakobshavn in Greenland in terms of speed of retreat. It drains 20% of the West Antarctic Ice Sheet, and has been estimated to possibly contribute 10 mm of GMSL rise in the next 20 years (Favier et al., 2014). Similar to Jakobshavn the cause of this rapid retreat and ice loss by discharge is attributed to melting as a result of a warmer ocean. If this picture is repeated across a number of the major outlet glaciers then the contribution to SLR could rapidly increase.

Speed of Pine Island Glacier as it reaches the sea. Source

Future

GCMs project an increase in precipitation in the Antarctic region that could actually increase SMB across the region and therefore contribute negatively to GMSL rise. Surface melt in Antarctica is minimal due to the consistently cold temperatures and is likely to remain so for the foreseeable future as a massive rise in temperatures would be required to have any effect. The worrying areas are glaciers that are grounded in the ocean, warming ocean temperatures are the biggest threat to Antarctic Ice Sheet stability, particularly in the West. It is possible on longer timescales that the East Antarctic could contribute significantly to SLR because of marine ice melting however this is very unlikely to occur before 2100 (Mengel & Leverman, 2014).