The greatest unknown about future sea level rise is the loss of the mighty Antarctic ice streams. The ice shelves in Antarctica provide a buttressing effect on the land-based ice streams. They hold the downward flow of the land glaciers from emptying into the sea by exerting a backward force to the downward force of the glacier streams. Ice shelves do crack and in the past have been considered localized phenomenon. But we are now learning that the disintegration of one ice shelf may induce a similar fate to its neighbor.
In this area of the Antarctic Peninsula, ice moves as if it is on a conveyor belt, flowing down between the mountain peaks and toward the ocean. You can see here it is building an ice moraine as it flows. This stretch of glaciers flows onto the Larsen catchment.Maggie Turin of the Institute of Columbia University reports on the example of the spontaneous but gradual retreat of the Larsen B ice shelf after the collapse of the Larsen A shelf in 1995.
It was January 1995, toward the end of the austral summer, when Larsen A, the smallest of the three shelves, broke apart rather suddenly and was gone. The furthest north of the Larsen trio, this small shelf was situated just north of the Larsen B and just outside of the Antarctic Circle. Due to its size and location, the 1,500-square-kilometer block of ice was the most vulnerable of the three Larsen shelves. Warming water that had been moving around the peninsula was the probable cause for the demise.
When Larsen A disappeared, Larsen B immediately became more vulnerable. Although twice the size at 3,250 square kilometers, the shelf was now un-buffered from warming ocean waters to the north; this combined with several warm summers and Larsen B weakened and became destabilized. In 1998, satellites captured evidence of the front edge of Larsen B beginning to change. Satellite images pointed out melt water ponds on the surface of the shelf, but with some 220 meters of ice thickness, these ponds did not seem to pose a threat. Then between early February and early March 2002, the shelf suffered a massive collapse, with section after section all but evaporating before our eyes. There was disbelief among the science community that a section of shelf this size, and one that had been relatively stable for an estimated 10,000-12,000 years, could so swiftly suffer a collapse. The second domino had fallen.
With the loss of a significant section of the Larsen shelf complex, there was a subsequent acceleration of the glaciers that had once been braced by the shelves’ protective presence. Without the stable pressure pushing back against these glaciers, the ice sheet in this area accelerated by up to 300 percent, transferring ice from the Antarctic continent into the ocean and contributing more ice to sea level rise. With the acceleration came a rapid loss in size in the glaciers feeding the Larsen area.
Larsen C remains the fourth largest of the ice shelves by a few hundred square kilometers of ice. A crack appeared in the shelf in 2011 and has grown in size over the subsequent years. Set back about 20 kms. from the edge of the shelf, it threatens to break off about 8 percent of the shelf, or a chunk of ice about the same size as the state of Delaware, at ~6,000 sq. km. With the crack set so far back, there is concern that it might threaten the integrity of the larger ice sheet, weakening the support that holds the shelf in place.
The below images are from NASA's Goddard Space Flight Center. There are some stunning videos of Larsen C that I am unable to embed. Please take time and check them out here.
Snapshot of the rift in the Larsen C on Nov. 10, 2016. (NASA/John Sonntag) Snapshot of the rift in the Larsen C on Nov. 10, 2016 x YouTube VideoMedia Matters has a must-read piece on our president-elect’s climate denial and the news outlets that are only making the problem worse. This is a very difficult time for those who believe in facts and science. I am finding that it is extremely difficult to not become depressed and disheartened with every new revelation of a climate change emergency now that climate change deniers and the fossil fuel industries hold positions of power in the next administration.
Studies have shown that most Americans don’t read beyond the headlines of news articles, most people who share articles on social media haven’t actually read them, and misleading headlines misinform people even when the body of the article gets the facts right. And that’s a huge problem when major outlets’ headlines are framed around President-elect Donald Trump’s latest false claims about climate change.
During a December 11 appearance on Fox Broadcasting Co.’s Fox News Sunday, Trump declared that “nobody really knows” whether human-induced climate change is happening. As is often the case in TV interviews with climate science deniers, host Chris Wallace didn’t challenge Trump’s claim, which blatantly misrepresents the consensus of the world’s leading scientific institutions that human activities such as burning fossil fuels are the main cause of global warming. But Wallace’s silence was just the first media misstep.
In the hours that followed, major media outlets including The Washington Post, CNN.com, United Press International, and International Business Times produced online headlines about Trump’s remarks that didn’t mention that they were false: