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Sea levels and Charleston: Expert says bring all players to the table

Posted on May 13, 2014 by in Place

Charleston among most cities at most risk, White House Climate Assessment, 2014

The “unstoppable” collapse of glaciers in Antarctica first reported on Monday has triggered a flurry of dire estimates about what the big melt will mean for higher sea levels, including in metro Charleston.  But there won’t be hard numbers until the actual report on the collapse is released.

Gary Mitchum, professor and associate dean at USF, 2014One of the leading researchers on sea levels in the Southeastern U.S., Prof. Gary Mitchum, a faculty member and associate dean at the College of Marine Science of the University of South Florida (photo at left), told Local America he is withholding comment until he sees the report produced by researchers at NASA and the University of California at Irvine. Mitchum, who grew up in Charleston, expects the study to be released by the end of the week.

How ice shelves are retreating in West AntarcticaMitchum is studying the abstract of the forthcoming report, which includes a map (image at right) showing the different rates of the “unstoppable retreat to the sea by ice shelves of melting glaciers in the West Antarctic. Shelves shown in red on the map are retreating most rapidly.

The abstract’s only reference to what the collapse of the glaciers would mean for future sea levels was this line, “This sector is of global significance since it contains enough ice to raise global sea level by 1.2 meters [4 feet].” The estimate, which is from a 2008 research paper reference, did not include any time frame.

Mitchum’s 2011 report projecting a 2.6-foot rise in regional Charleton sea levels by 2100 is one of the key documents cited by the National Climate Assessment — released by the White House late last week — which pinpointed Charleston as one of the coastal areas “most at risk” from rising sea levels.

Mitchum said the 2.6-foot number was significant by itself, regardless of how the West Antarctic melt is quantified and interpreted in coming days, weeks, months. Besides, he said, the 2.6-foot number would most likely keep increasing beyond 2100 unless there was major action to reduce man-made global warming. The National Assessment, backing up the recently updated United Nations report on climate change, said carbon pollution was the main factor behind global warming.

Mitchum said it was up to local and state government to be the lead actors in reducing global warming. “Every city, county and region should be sitting down with scientists, economists, policy makers, planners and developers so they can produce the best strategy,” he said.

From Local America’s earlier coverage about the collapse of the West Antarctic glaciers and the earlier released National Climate Assessment:

Melting glacier ice sheetsResearchers from NASA and the University of California at Irvine said on Monday that six glaciers in the West Antarctic (see NASA map above showing melting glacial ice sheets in red) are in an “unstoppable” retreat that is dumping the sheets in the water and setting in motion long-term rising sea levels worldwide. The retreat is irreversible, says lead report author and geologist Eric Rignot, primarily because there are no land masses under the glaciers to act as a barrier.

Rignot there’s enough frozen water in the retreating glaciers to raise sea levels by 4 feet. The big question is, What’s the time line for this 4-foot increase to happen? “This sector [the six melting glaciers] will be a major contributor to sea level rise in the decades and centuries to come,” Rignot says. “A conservative estimate is it could take several centuries for all of the ice to flow into the sea.”

Mitchum’s 2011 “Sea Level Changes in the Southeastern United States, Past, Present and Future,” one of the studies cited in the National Climate Assessment, says:

“[The] present best guess for our region is 80 centimeters [2.6 feet] of sea level increase by 2100. This estimate, however, is more likely to be too low than too high.”

Mitchum’ s baseline estimate of a 2.6-foot rise represents a 240% increase in what was recorded in a century of sea-level measurements in Charleston Harbor extending to current times.

This guide from Climate Central shows the estimated flooding impact on population and housing in the Charleston region from foot-by-foot increases in the sea level.

Thwaites ice shelf in West Africa calving in 2012, James Yungel, NASAMitchum says global warming is the main cause for the faster rise of sea levels. He and many other scientists says global warming is melting ice sheets in the Arctic and Antarctica.  One example is the breakup of the massive Thwaites Glacier in West Antarctica (photo above). The melting ice has only one place to go: the sea.

The White House Climate Assessment echoes the recently updated United Nations report on the threat of global warming. “Climate change is affecting us right now, and the carbon pollution that causes it is a threat to our health and the environment,” the White House said in a statement accompanying the report.

Mitchum’s study is based heavily on measurements of the melting of Greenland and Antarctic ice sheets, which has been accelerating in recent decades. The study says the accuracy of measurements has increased “dramatically” with the use of altimeters on satellites circling the Earth. Gages like the one long used in the Cooper River in Charleston are subject to tidal fluctuation and consequently aren’t considered as exact.

The National Climae Assessment cited a 2012 report that says 25,000-50,000 people in the Charleston region are “at risk” from flooding because of rising sea levels. The “lowcountry” has always been vulnerable because some of it is less than 1 meter above high tide.

Minor flooding from higher sea levels is already occurring in downtown areas of Charleston, particularly at Lockwood Drive-Wentworth Street. (The details are in this Local America Charleston article.) The flooding can increase when storm surges in the tidal Cooper and Ashley Rivers are intensified by higher sea levels.

Credit for map at top of page: National Climate Assessment, May 2014.

Photo credit for ice sheet of collapsing Thwaites Glacier in the West Antarctic: James Yungel, NASA.

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