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Wednesday, January 14, 2015

John Abraham: The Antarctic ice sheet is a sleeping giant, beginning to stir

Infrastructure must adapt to shrinking southern ice sheets and sea level rise

This undated photo courtesy of NASA shows Thwaites Glacier in Western Antarctica.

This undated photo courtesy of NASA shows Thwaites Glacier in Western Antarctica. Photograph: AFP/Getty Images

by John Abraham, "Climate Consensus - The 97%," The Guardian, January 14, 2015

In a paper I just published with colleague Dr Ted Scambos from the National Snow and Ice Data Center, we highlight the impact of southern ice sheet loss, particularly the West Antarctic Ice Sheet, on sea-level rise around the world.
We know that human emissions of greenhouse gases are causing the Earth’s temperature to rise and are creating other changes across the Earth’s climate system. One change that gets a great deal of attention is the current and future rates of sea-level rise. A rising sea level affects coastal communities around the world; approximately 150 million people live within 1 meter of current sea level.
The waters are rising because of a number of factors. First, water expands as it warms. In the past, this “thermal expansion” was the largest source of sea-level rise. But as the Earth’s temperatures continued to increase, another factor (melting ice, particularly from large ice sheets in Greenland and Antarctica) has played an ever increasing role.
In the Southern Hemisphere, the largest player is the Western Antarctic ice sheet (WAIS). It is less stable than Eastern Antarctica and is particularly vulnerable to melting from below by warmed ocean waters. Scientists are closely watching the ice near the edges of the WAIS because they buttress large volumes of ice that are more inland. When these buttressing ice shelves melt, the ice upstream will slide more rapidly toward the ocean waters. 
As reported in our paper, according to some studies, “no further acceleration of climate change and only modest extrapolations of the current increasing mass loss rate are necessary for the system to eventually collapse ... resulting in 1-3 metres of sea-level rise.” And this is from just one component of the great southern sheets.
What we also discuss is that sea-level rise will not be uniform. Antarctica (and Greenland) are currently losing gigatons of ice each year. That ice is heavy, and we know from first-year physics courses that mass (particularly heavy items) expresses a gravitational attraction. So, all that ice sitting atop Antarctica is pulling ocean waters toward it. 
As the ice melts, the gravitational force will lessen, and the waters will “slosh” away from Antarctica. In our paper, we report that sea level rise in the Northern Hemisphere will be greater than the world-wide average, whereas sea levels in the region next to Antarctica may actually fall. This means that infrastructure planning on the east and west coasts of North America, as well as in Europe, must be prepared for a greater than average sea-level rise.
This is an exciting and rapidly evolving field of study that has tremendous implications for coastal communities and infrastructure. My colleague, Dr Ted Scambos, summarized the current knowledge by saying,
Antarctica’s ice sheet has been called the ‘sleeping giant’ of sea level, but it’s beginning to stir. Everything we’ve seen about this change points to human influences on climate – and now we’re at the point where human actions will be needed to stop it. 
We will be eagerly awaiting more results on this subject over the next few months and years.

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