The glaciers of Greenland and Antarctica hold 90% of the world’s fresh water. Due to the greenhouse effect and global warming, these glaciers are calving at an accelerated rate. And if this continues glacial melt could raise the sea level worldwide enough to swamp coastal communities on every shore. An accelerating crack in the ice shelf known as Larsen C, the fourth-largest ice shelf in Antarctica, could be the next biggest threat.
Daniel Douglass, lecturer in the Department of Marine and Environmental Sciences and an expert in Glacial Geography at Northeastern University, explains why ice shelves form, what causes them to crack, and how they affect the environment.An ice shelf is created when a glacier—ice that is moving over land—enters the ocean. “The ice will float up and the ocean will flood under, thereby creating the ice shelf. An ice shelf can be anywhere from a hundred to a few thousand feet thick. It becomes progressively thinner toward the outer edge of the glacier,” he explains.
The crack in Larsen C is now one-third of a mile deep, slicing through to the ice-shelf floor, and is, in total, more than 100 miles long and is about to calve. Calving is the process whereby pieces of ice break off the thinner, outer edge of the ice shelf to create icebergs. Ice shelves are different from sea ice, which forms when ocean water freezes.
“A warming climate can contribute to calving in two ways. First, if the ice shelf is exposed to warmer air above and-or warmer water below, then there will be more rapid melting of the shelf. Second, if water formed by the melting of the glacier’s snow or ice has accumulated on the surface of the glacier and filled surface crevasses—cracks on the glacier’s surface that do not go all the way through—then the water pressure at the bottom of the crevasse can widen and deepen the crack, potentially wedging all the way through the ice shelf, facilitating the calving process,” explains Douglass.
Ice shelves act as buttresses to keep glaciers from flowing into the ocean. If the disintegration of ice shelves continues the rise sea levels will accelerate.” Sea level rise has the potential to be the most expensive consequence of global climate change. Many of the world’s largest cities grew in coastal environments because the nearby ocean facilitated transportation (shipping) and provided food (fishing),” he adds.
“Calving is an inevitable consequence of glaciers flowing into oceans. There are probably giga-technologies (very large-scale engineering processes; the extreme opposite of nanotechnologies) that could close the rift that has formed in Larsen C and suture the loose piece back onto the glacier, but I don’t think that would be a good allocation of resources. That ice is already in the ocean, and the calving event itself does not cause sea level rise until the land-based glacier accelerates into the ocean” he says, ” The long-term solution is to stabilise the Earth’s climate so that glaciers don’t continue to melt, thin, and accelerate into the ocean. The obvious place to start would be to reduce the number of fossil fuels that are used in the global economy.”