According to new studies the melting of the West Antarctic ice sheet is unstoppable, it is occurring faster than predicted and has ‘passed the point of no return.’ Thwaites Glacier in Antarctica. Image © NASA
The study, led by glaciologist Eric Rignot at NASA’s Jet Propulsion Laboratory, Pasadena, California, and the University of California, Irvine, follows decades of research and theory suggesting the West Antarctic Ice Sheet is inherently vulnerable to change.
The new finding that the eventual loss of a major section of West Antarctica’s ice sheet “appears unstoppable” was not completely unexpected by scientists who study this area.
Antarctica is so harsh and remote that scientists only began true investigation of its ice sheet in the 1950s. It didn’t take long for the verdict on the West Antarctic Ice Sheet to come in. “Unstable,” wrote Ohio State University glaciologist John Mercer in 1968. It was identified then and remains today the single largest threat of rapid sea level rise.
The defining characteristic of West Antarctica is that the majority of the ice sheet is “grounded” on a bed that lies below sea level.
In his 1968 paper, Mercer called the West Antarctic Ice Sheet a “uniquely vulnerable and unstable body of ice.” Mercer based his statement on geologic evidence that West Antarctica’s ice had changed considerably many, many millennia ago at times when the ice sheets of East Antarctica and Greenland had not.
In 1973, University of Maine researcher Terry Hughes asked the question that scientists continue to investigate today. The title of his paper: “Is The West Antarctic Ice Sheet Disintegrating?” In 1981, Hughes published a closer look at the Amundsen Sea region specifically. He called it “the weak underbelly of the West Antarctic ice sheet.”
Here’s the cause for concern: When the ice sheet is attached to a bed below sea level, ocean currents can deliver warm water to glacier grounding lines, the location where the ice attaches to the bed.
Scientists recognized that this is the first step in a potential chain reaction. Ocean heat eats away at the ice, the grounding line retreats inland and ice shelves lose mass. When ice shelves lose mass, they lose the ability to hold back inland glaciers from their march to the sea, meaning those glaciers can accelerate and thin as a result of the acceleration. This thinning is only conducive to more grounding line retreat, more acceleration and more thinning. In this equation, more ice flows to sea every year and sea level rises.
But that’s not all.
Beginning with research flights in the 1960s that made radar measurements over West Antarctica, scientists began to understand that, inland of the ice sheet’s edge, the bed slopes downward, precipitously, in some cases.
This downward, inland slope was theorized decades ago, but has been confirmed and mapped in detail in recent years by airborne campaigns such as NASA’s Operation IceBridge. In some spots the bed lies more than a mile and a half below sea level. The shape of this slope means that when grounding lines start to retreat, ocean water can infiltrate between the ice and the bed and cause the ice sheet to float off its grounding line.
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