Gravity is Not Our Friend This Time
(Published in The EarthSphere Blog. Cover Image: Glacial Collapse by WM House and CF Lovelace; ArcheanArt)
A flurry of news reports on Antarctica’s Thwaites Glacier reached the headlines recently. The Glacier, also dubbed the “Doomsday Glacier” by some of the more dramatic renditions of the story, is a huge chunk of ice about the size of Florida. But that description doesn’t do it justice. Florida is just a flat piece of land perched at sea level (or lower). If parts of Florida rose 4000 feet above sea level, we would get a better picture of the volume of ice in the Thwaites Glacier. Perhaps a better way to envision this mother lode of ice is through the two feet of global sea-level rise it would cause by melting.
Recent revelations about the threat posed by the Thwaites Glacier are not new. The show has already started, and we are tuning in midstream. Since 2000, the Glacier has shed a trillion tons of ice into the world’s oceans. The meltwater from this single Glacier accounts for about four percent of the planet’s seal-level rise each year.
But all I’ve said so far is old news. The new fuss concerns what Ron DeSantis might call left-wing stuff; scientific research to be precise. It’s true, scientists have been poking around investigating both the obvious and not so obvious. Observing ice melting on the top of the Glacier as Earth warms is the easy part. However, what’s happing below the Glacier, along its base, is even more alarming than events at the surface. The base of the Thwaites Glacier is melting. A melting base translates into a loss of friction, allowing the entire Glacier to slide seaward as gravity takes hold and does its thing.
Sea Ice versus Coastal Glaciers
The Arctic freezes over every year with a sheet of sea ice several meters thick. Much of this ice melts the next summer. Granted, the winter freeze is not as robust as 50 years ago, and the Northwest Passage is becoming a reality, but winter ice still forms. This type of sea ice is not, I repeat, “Is Not!” the same as the ice composing the Thwaites Glacier.
Antarctica’s thick ice shelves are not the result of normal sea ice formation. Instead, they result from onshore glaciers extruding ice from the continent onto the ocean’s surface. The transfer of mass from onshore to offshore allows the ocean portions of these glaciers to be thousands of feet thick. An ice shelf collapse occurs when the entire shelf cannot sustain itself, and a glacier’s edge retreats to the coastline.
Ocean warming is a relative term. In the case of Antarctic waters, a temperature of 0 degrees Celsius (32 degrees Fahrenheit) is warm. Yes, this is the freezing point of water, but it only applies to freshwater. Seawater freezes at -2 degrees Celsius (28.4 degrees Fahrenheit), due to its salinity. So, the temperature dynamics at the base of an ice shelf require that the salt water under the ice remains below the freezing point of fresh water, thus keeping the ice from melting.
Several years ago, a multimillion-dollar research project drilled through 610 meters (2000 feet) of ice and measured ocean temperatures below the Thwaites Glacier. The drilling project investigated a spot at the “grounding line” of the Glacier. A “grounding line” is the location where a glacier passes from the land and extends out over the ocean. The temperature of the water below the Thwaites ice was zero degrees Celsius; warm enough to induce melting.
Gravity and Warming
Melting the ocean portion of the Thwaites Glacier is like removing the soil at the bottom or toe of a slope. Eventually, this loss of stability causes the whole slope to slide downward. As ice disappears from the toe of the Thwaites Glacier, the upper, land-based parts of the Glacier will slide seaward, and like dumping a large block of ice into a bathtub, sea level will rapidly rise.
Recent alarm over the Thwaites Glacier is the result of research indicating the base of the Glacier is warming faster than expected. There are three sources of heat creating this problem. The first and most visible source is sunlight, solar radiation. During the summer, the dark ocean waters absorb a lot of solar heat, and surface waters may overheat, enhancing melting at the base of ocean ice.
The second source of warmer water is meltwater runoff from land. Commonly, glacial melting creates streams at the base of the ice where it rests on solid ground. In the case of coastal glaciers, these meltwater streams flow beneath the ice and into the ocean. This process introduces warmer waters that mix with the existing ocean water and raise temperatures.
The third, and probably most important, source of warm water is from the deep ocean. The Antarctic Circumpolar Current dominates the Southern Ocean. Driven by westerly winds, this current endlessly circles Antarctica, and it facilitates upwelling, so deep ocean waters are driven to the surface. These waters are cold but warmer than the Arctic coastal waters. Hence, the shallow oceans warm as deep-ocean water mixes with the Antarctic coastal water.
Despite the current political dismissals of threats from climate change, a rapid 2-foot rise in sea level would be bad news for Florida, Ron DeSantis, and the rest of the world. This threat is what the fuss is about.
Related Stories:
The collapse of Antarctic ice shelves (WM House; ArcheanWeb)
Collapsing Antarctic Ice Shelves (WM House; Medium)
The Antarctic Circumpolar Current: An Ouroboros (by WM House; ArcheanWeb)
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Sources:
The “Doomsday Glacier” may partially collapse. If it does, Earth’s sea level will rise by 2 feet (by Matthew Rozsa; Salon)
Ocean temperature impact on ice shelf extent in the eastern Antarctic Peninsula (By Johan Etourneau, Giovanni Sgubin, Xavier Crosta, Didier Swingedouw, Verónica Willmott, Loïc Barbara, Marie-Noëlle Houssais, Stefan Schouten, Jaap S. Sinninghe Damsté, Hugues Goosse, Carlota Escutia, Julien Crespin, Guillaume Massé & Jung-Hyun Kim; Nature Communications)
Glacial meltwater dynamics in coastal waters west of the Antarctic peninsula (By Heidi M. Dierssen, Raymond C. Smith, and Maria Vernet; PNAS February 19, 2002 99 (4) 1790–1795)
Unprecedented data confirms that Antarctica’s most dangerous glacier is melting from below (By Chris Mooney; Washington Post)
