The threat of ice melting from the West Antarctic ice sheet may be less than expected

A recent study said that, while all or part of the western Antarctic ice sheet melted as a result of global warming, it would not raise the sea level to some as predicted, the water level The seas in US coastal areas are 25% higher than the world average sea level, directly threatening cities such as New York, Washington, DC, and San Francisco.

In terms of sea level rise, people have long been liking Antarctica as a sleeping giant. According to calculations, the Antarctic ice sheet is nine times more abundant in Greenland. The Western Antarctic ice sheet, called WAIS, attracted the attention of many scientists because of its inherent instability. This instability is due to the majority of the ice mass below sea level.

Jonathan Bamber, lead author of the study published in the journal Science on May 15 last about the WAIS ribbon, said: 'A series of studies on the possibility of collapse and melting. of WAIS tapes allude to a dangerous disaster to the earth. All of these studies estimate that if the ice sheet melted, the sea level would rise from 5 to 6 meters. However, according to our calculations, those calculated numbers are too high even for a thousand years. '

Bamber, a professor at Bristol University in the UK, is currently studying at the University of Colorado at the Boulder Institute for Environmental Research Cooperation (Boulder's Cooperative Institute for Research in Environmental Sciences), abbreviated as CIRES and his colleagues calculate. that if the WAIS ice sheet collapses and melts, it will raise sea level to 3.3m or 11 feet.

The study authors used models based on glacial theory to study what this giant ice sheet would look like if icebergs collided with it and broke free. Currently, large bands are preventing WAIS from drifting down the Weddell and Ross seas, limiting losses to the ocean.

In theory, if the icebergs were moved, many relatively large areas of the WAIS would basically no longer be hindered as before. WAIS tapes will float to the sea and begin a process of rapid invasion through separators. The median strip is where the edge of the ice reaches the sea and begins to float.

Most of the unstable areas of the giant WAIS ice sheet are located in deep areas below sea level. If the ice in these low-lying areas is no longer held by the floating ice sheet, it quickly rises and forms a new floating ice sheet, separating itself, and causing many other collapses and faults.

Icebergs in Paradise Bay west of Antarctica (Photo: iStockphoto / Micheal O Fiachra)

The authors studied each assumption that only ice on the slope and inside of low-lying areas would likely collapse.They also assume that ice on reefs with a slope upward and on reefs above sea level is unlikely to fall.

Professor Bamber said: 'Unlike most other ice sheets in the world, West Antarctic ice sheets and Greenland - WAIS are the only cases with such unstable structure'.

However, how quickly the WAIS ribbon will collapse and melt, there is absolutely no answer. If the ice sheet melted within 500 years as suggested by previous studies, it would increase the sea level by 6.5 meters or ¼ inch a year. This number is double the annual sea level rise due to all factors combined.

Professor Bamber adds: 'An interesting thing is that the annual sea level rise model does not depend on how fast and how much WAIS ice melt. Even if the WAIS ice sheet contributes to an increase in sea level of 1 meter over many years, the sea level along the North American coast will still increase more than the world average of 25%.

According to the study, regional sea level changes will largely be influenced by the distribution of ice blocks from the Antarctic continent to the oceans. With little concentration of ice sheets on the South Pole, the gravity of the earth will weaken in the Southern hemisphere and be stronger in the Northern hemisphere. This will cause water to flow to the ocean in the north.

This redistribution will also affect the rotation of the earth, which will then cause water to rise along the North American continent and in the Indian Ocean.

The co-authors include Riccardo Riva and Bert Vermeersen from Delft University of Technology in the Netherlands and Anne LeBroq from the University of Durham in England. The study was conducted with the help of the Natural Environment Research Council.

References:
Jonathan L. Bamber, Riccardo EM Riva, Bert LA Vermeersen and Anne M. LeBroq.Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet.Science, 2009;324 (5929): 901 DOI: 10.1126 / science.1169335