In 1978, John Mercer of the Institute of Polar studies stated, “One of the warning signs that a dangerous warming trend is underway in Antarctica will be the breakup of ice shelves on both coasts of the Antarctic Peninsula.” The warning signs are now flashing red!
The West Antarctic Peninsula is a string of ice covered, bedrock islands stretching over 800 miles northward from Antarctica toward the southern tip of South America. For thousands of years, the peninsula’s land based glaciers flowed slowly into the ocean, held back by the grounded ice shelves along the peninsula’s coastlines. But these ice shelves are disintegrating.
John Abraham wrote in The Guardian on June 12, “When an ice shelf melts or collapses, it can unpin other ice that is sitting on land, which allows it to flow more quickly into the ocean. It is this secondary effect — the loss of ice resting on land — that changes the rate of sea level rise.”
On the eastern Peninsula coast, the northernmost section of the Larsen Ice Self Complex, Larsen A, lost about 580 square miles of ice in an abrupt event in January, 1995. Just to the south, during the Southern Hemisphere summer of 2002, the Larsen B Ice Shelf collapsed in just over one month. Scientists had never seen such a large area, 1,250 square miles, disintegrate so rapidly. Following the Larsen B collapse, NASA scientists reported the Larsen A and B land based glaciers experienced an abrupt acceleration, about 300 percent on average, and their mass loss went from 2-4 gigatones per year in 1996 and 2000 (a gigaton equals one billion metric tons), to between 22 and 40 gigatons per year in 2006. Beginning in February 2008, the Peninsula’s Wilkins Ice Shelf, on the western side of the Peninsula, disintegrated in a series of breakup events. The last remnant of the northern part of the Wilkins Ice Shelf collapsed in early April 2009. It was the tenth major ice shelf to collapse in recent times.
Recently, a piece of the Peninsula’s Larsen C Ice Shelf, the fourth largest ice shelf in Antarctica, has broken off. The Larsen C Ice Shelf had developed a 120-mile-long crack with only 8 miles to go before it became one of the largest icebergs ever recorded. The “calving” of this 2,300 square mile, 1,150 foot thick piece of ice — the size of Delaware — is the most recent Peninsula ice shelf disintegration event.
In a National Geographic article from November 3, Brenda Ekwurzel, Senior Climate Scientist with the Union of Concerned Scientists, wrote: “Losing all the ice shelves of Antarctica would be like losing each flying buttress that supported a gothic building. Collapse is the inevitable result. The question is how fast is the collapse in the case of an ice sheet that would, as Richard Alley told Congress in February 2007, ‘slowly spread outwards and flatten like pancake batter that was just plopped on a griddle.’ Nearly a decade later, the latest science indicates a critical threshold may have already been crossed.”
A report published in the journal Nature in March by Dr. David Pollard of Pennsylvania State University and Dr. Robert DeConto of the University of Massachusetts, Amherst, concluded that the West Antarctic ice sheet alone could raise sea level as much as three feet by the end of this century. And with ice melting in other regions, sea level could reach five or six feet — roughly twice the increase reported as a plausible “worst-case” scenario by the United Nations just three years earlier.
An online interactive article in The New York Times, Sunday Review from April 2016 shows two dozen U.S. coastal areas that would be permanently flooded at sea level rise of 5, 12, and 25 feet. Examples of cities with the percentage of land that will be permanently flooded at five feet of sea level rise: Boston, 9 percent; Cambridge, 26 percent; Charleston, 19 percent; Galveston, 68 percent; Miami, 20 percent; Jersey City, 20 percent; Atlantic City, 62 percent; New York City, 7 percent; and New Orleans, 88 percent. But sea level rise will not stop at five feet, it will accelerate and it will become unstoppable, if it hasn’t already.
A NOAA website indicates the global surface temperature during the last (Eemian) interglacial period, 125,000 years ago, was warmer than pre-industrial by about 1 to 2 degrees Celsius. A study published in the journal Nature Geoscience in December 2007 found that during the Eemian, sea level was up to 30 feet higher, and the average rate of sea-level rise was about five feet per century.
Two degrees Celsius above pre-industrial is the temperature scientists have been warning us about. It will require maximum effort of all nations to stay below 2 degrees, and even that will not stop the ocean from rising. What level of sea rise will convince us to act?
William Gran, now retired, was an adjunct instructor at Greenfield Community College on global warming and climate change. He can be reached at whgran@gmail.com