It’s worth being reminded occasionally of the stunning scale of the world’s great ice sheets and the glaciers that connect them with faraway coasts when cleaved icebergs (and flowing meltwater) outweigh the gain of mass from snowfall in the frigid interior, contributing to sea-level rise.
Back in 2004, after exploring Greenland with climate scientists, I tried to find a fresh way to describe the vast island’s ice mass and — working with topographic maps and ocean charts — came up with this comparison:
For scale, think of it as a freshwater Gulf of Mexico that has been frozen, inverted and plunked atop the world’s largest island.
You can see my video tour of Greenland here.
Chris Mooney has filed a nice Washington Post piece on ice sheet dynamics and several ways to visualize the most common unit of what’s moving to the sea — gigatons (each a billion tons):
[C]onsider how Meredith Nettles of the Lamont-Doherty Earth Observatory at Columbia University recently described a gigaton-sized piece of ice to me: “If you took the whole National Mall, and covered it up with ice, to a height about four times as high as the [Washington] monument,” says Nettles, you’d have about a gigaton of ice. “All the way down from the Capitol steps to the Lincoln Memorial.”
Another option is to use the Empire State Building as a yardstick. A week ago, I received a note and video clip from New York University glacier researchers Denise and David Holland that gives a fresh sense of scale to the ice flowing into the Ilulissat Icefjord from the Jacobshavn Glacier, the most productive river of ice in the Northern Hemisphere. (They are using radar and seismic sensors over several years to gain a more precise understanding of the physics of iceberg calving where such ice streams meet the sea.)
They caught a fresh calving event and described the cleaved slab as being about the height of two Empire State Buildings. In the video you can watch it slide down from the face of the glacier, then bob (such a word is pretty inadequate for something so large) to the surface before heading out toward the sea.
It was by no means an unusual moment.
The Jacobshavn glacier has slowed since the extraordinary surge in 2011 and 2012, the period when the “Chasing Ice” documentary team caught the largest documented ice calving event ever recorded (with the sound as hair prickling as the imagery). (I never got around to posting a conversation I had in 2014 with the film’s director, Jeff Orlowski, and two climate researchers, so here it is now.)
Here’s Denise Holland’s description of the research project, which is aimed at improving how computer simulations of the climate and ocean project sea level changes driven by the erosion of ice sheets:
Global sea level rise is one of the most often cited potential large impacts of global climate change over the coming century. Within the problem of sea level rise itself, the most difficult aspect to deal with from a future projection point of view is the physical process of glacier calving. This process is poorly understood due to a lack of physical observations, a consequence of the difficult and dangerous nature of the calving process in which massive pieces of ice are transferred from the land to the ocean. To obtain measurements of calving we therefore use remote sensing techniques, which include both radar and seismic instrumentation. An interferometric radar pointed at the glacier front provides measurements of the surface velocity of the glacier at very short intervals. A broadband seismic array surrounding the glacier front provides information on glacier fracturing beneath the surface. These observations are being collected in our project over a period of several years as we build up a statistical data base of calving events. Hopefully this data set will give us insight into how and why calving occurs so that we can create a parameterization to be used in climate models that includes glaciers and their calving. This will lead to more robust projections of sea level rise than is currently possible.
Vice News picked up on the story and recently produced an illuminating Greenland film.
For the latest on Greenland’s ice conditions, visit Current Surface Mass Budget of the Greenland Ice Sheet, a website maintained by the Danish Meteorological Institute.