The ice shelf didn't just calve off the way the sheets of ice pushed into the ocean by the glaciers that formed them always do. If that were the case, it would have made for a big iceberg, about the size of Rhode Island, but nothing too extraordinary. Calving is the inevitable fate of ice pushed into the ocean by the glaciers. And the Larsen B, like the Larsen A before it, was expected to break off. Larsen A broke off in 1995, but since it was only 4,000 years old and was showing signs of calving, it came as no surprise to anyone. But Larsen B, older than the Holocene, was believed to be more stable, and would take much longer to calve off. However, it was the disintegration that was shocking.
Scientists had realized that warming ocean currents were eroding the ice shelf from underneath. The warming was only a degree or so, but that was twice as far above freezing as it had been, and had a much faster effect on the ice. Further, the millions of ice lakes and puddles that formed on the surface of the ice shelf each summer melted into the ice, acting like a million little wedges. A million little ice bergs have a far higher surface to volume ratio than does one big iceberg, and in just three years what had been the Larsen B ice shelf had completely melted away. Had it remained a giant iceberg, it may have lasted dozens, even hundreds of years.
It didn't have any effect on sea levels, of course, since it was already in the water. But its disappearance meant that the warm ocean currents now had an open route under the Larsen C, an ice shelf nearly four times as large as Larsen B. Previously regarded as stable, that ice shelf is expected to vanish within ten years.
For years, glaciologists had debated what role the ice shelves had in bottling up the glaciers. The collapse of the Larsen B answered that. The shelves are a very effective cork, and if you remove that cork, the glaciers pour into the ocean.
Worrisome as all this might be, major alarm focused on the portion of the Antarctic that lies on the other side of the Peninsula, the West Antarctic Ice Sheet (WAIS). Most of Antarctica's ice sheet lies above sea level, and much of it is cordoned off by mountains. In the WAIS, however, are several huge glaciers—any of which would be the largest in the world if outside of Antarctica, and much of the land under the glaciers is under sea level, so water – warm water – is seeping in and lubricating the glaciers.
Concern about the WAIS predated worries about global warming. Clear back in 1973, T. Hughes of the Institute of Polar Studies, The Ohio State University, Columbus, Ohio, wrote a paper, “Is The West Antarctic Ice Sheet Disintegrating?”. He wrote, “Data pertaining to the dynamics and history of the west antarctic ice cover are reviewed and interpreted in terms of a possible inherent instability of the ice cover. A study of published data concerning the past and present ice cover of West Antarctica indicates that during the last few million years the ice sheet has been retreating in stages, each retreat stage being preceded by an advance of comparable duration. Thus disintegration of the west antarctic ice sheet seems to follow the disintegration pattern of other continental ice sheets and may be the last phase of the worldwide Late Cenozoic ice age. At least some of the retreat stages seem to have been rapid enough to be called surges. Stages of advance seem to have temporarily introduced equilibrium conditions, since equilibrium ice sheet surface profiles can be reconstructed from the moraines, etc., and thus mark the stable limits of each advance. Present ice sheet surface profiles along flowlines entering both the Ronne and the Ross ice shelves from Marie Byrd Land are not equilibrium profiles, suggesting that the west antarctic ice sheet is unstable. An analysis of the grounded portion of the west antarctic ice cover indicates that data relating to the surface profile, ice velocity, and the mass balance are all incompatible with an equilibrium ice sheet. Instability seems to be centered in the major ice streams that drain Marie Byrd Land. An analysis of the floating portion of the west antarctic ice cover indicates that basal melting is most pronounced along the Siple Coast of the Ross ice shelf and causes retreat of the grounding line into Marie Byrd Land. Instability seems to be related to sudden retreats of the grounding line.”
Nineteen seventy three was just about when Al Gore was first learning about the hazards of CO2 emissions. Within a few years, scientists were beginning to focus on the idea of global warming, and debating the effect they would have on glaciers. However, WAIS, being as it is, a vast unstable ice sheet, 800 miles from the nearest base, is one of the most inaccessible areas on earth. By 2006, more humans had visited the moon than had stood on any of the WAIS glaciers.
In 2006, the British Antarctic Survey began careful measuring, and the results were deeply disturbing. The three biggest glaciers, the Pine Island , Thwaites and Smith Glaciers , gain about .1% of their total mass each year, mostly from snow and ice crystals blown off the main part of the Antarctic ice cap. However, they lose about .16% per year, and that rate of loss is increasing at the rate of roughly 6.5% per year. It doesn't sound like much, does it? It means the ice shelf is doomed, and probably within the lifetimes of most people reading this.
The rate of melt was one hundred times what scientists had expected.
In 2011, satellite imagery caught a spectacular picture of an immense crack in the Pine Island Glacier, nineteen miles long, 260 feet wide and 195 feet deep. Disturbingly, the crack appeared in October, which is very early spring in that part of the world. Obviously things were changing ever more rapidly in the WAIS.
This year, the Brits returned to Pine Island Glacier, and sent a remote operated vehicle (another David Cameron idea) under the ice shelf to measure water temps and find out how fast the ice was being eroded from underneath.
The results were horrifying. It was believed that the vast Pine Island Glacier was anchored on a ridge of land at the edge of Antarctica, keeping it more-or-less moored. The operators of the ROV found themselves 30 miles “inland”, and for as far as they could see, the glacier was resting, not on land, but on a vast pool of warming water.
And it was moving at ten times the rate the 1973 figures suggested it would be moving at. That's with the ice shelf in place still, so the supposition is that the ice behind the glacier is putting more pressure on to flow to the sea.
The Thwaites Glacier is another huge glacier, and is moving unusually fast. However, the 2011 survey revealed that there is a 700 foot ridge that has the glacier anchored, slowing it, although nobody knows for how long.
Nobody knows what will happen next, because we simply have no experience at all dealing with these conditions. Either of those glaciers are bigger than all the glaciers in North America combined, and of course, only a few, relatively tiny glaciers in Greenland have an ice cap pushing on them. It's certainly nothing to compare with the WAIS.
The WAIS itself is on the move. Chris_Rapley, head of the BAS in 2006, warned then that there were early signs that the WAIS itself was beginning to disintegrate. Nobody knows what will happen. If you happen to be the type who likes to conjure up nightmare scenarios of blocks of ice, a thousand feet tall and the size of Ohio, rushing to the sea at forty miles an hour creating horrific 2,000 foot tsunamis, feel free. It's even hypothetically possible. If you believe that, and you live anywhere along the west coast of the Americas, you might consider moving to Colorado. Or maybe Mars.
If you're a bit more level-headed, you will feel concern over the fact that a body of ice capable of raising ocean levels by ten feet appears to be getting ready to disintegrate and fall into the ocean, and if it happens in the next twenty years, then we lose most of our coastal cities and 10% of our arable land. Not to mention vast changes in the climate and ocean currents.
The BAS is now conducting a vast electronic sweep of the glaciers and the ice cap, compiling the most detailed look at the topography of the region in hopes of getting some idea of where the ice is going, how fast it's going there, and how fast the land it rests on will rise once relieved of the burden of billions of tons of ice.
Meanwhile, right wingers in America howled with joy and derision at the news that temperatures plunged to minus -62F in Alaska last week. It was just more proof, in their eyes, that global warming was nothing more than a communist conspiracy theory that exists only to annoy honest businessmen like BP or Exxon. Of course, while it was the coldest Alaska had seen in a decade, forty years ago a day where it hit -62 might be referred to by the locals as “Wednesday.”
Lost in the celebration was the news that the Arctic Ice Cap, approaching its winter maximum late this month, is on course for the smallest maximum ever recorded, despite the Alaskan cold snap.