Ice breakup

The explosiveness of the recent breakup of part of the Wilkins Ice Shelf requires some explaining. I propose the following mechanisms:

1) Continued post-glacial rebound of the Arctic moves the earth's center of gravity toward the North Pole in the long term, pulling the center of mass of the hydrosphere northward, but reshaping the lithosphere as well, leaving no net change of sea level in Antarctica.
2) Seasonal snow in the Northern Hemisphere concentrates ocean mass toward the North Pole, reducing average sea level globally, and moving the earth's center of gravity a few inches northward on a seasonal basis, reaching a maximum in late winter or early spring. The weight of snow in the north pushes the lithosphere southward relative to the hydrosphere.
3) These mechanisms combine to "float" the Antarctic continent with its attached ice shelves, lifting the ice shelves beyond their natural flotation, and producing significant lateral stress.
4) The outer edges of the ice shelf sag downward due to the slight flexibility of the ice, which increases where the ice is thinnest. This sagging means that the outer ice floats better, and reduces the stress on the inner ice by contributing to its flotation.
5) Though the outer ice undergoes less stressing, it is after all, thinner and weaker, and may be the first to fracture under the gravitational stress.
6) Once it fractures its contribution to the flotation of inner ice is removed, leaving the inner ice even more stressed and vulnerable to fracture, and leading to the potential for a cascading effect, even an explosive one.

The question arises, is this due to global warming or unusually high snowfall in the northern hemisphere? The explosive mechanisms suggested, and their seasonal timing clearly implicate northern snowfall, but the outer ice is presumably weakened because of temperature rises. What other factors are involved in ice shelf formation and destruction?

1) The extent of an ice shelf is determined by its flow rate less its rate of melting.
2) Its flow rate is determined by the rate of snowfall contributing to its source, and
3) the depth and temperature of its flow fields.

All these factors are temperature related or equivalent, and it is no obvious deduction that any particular breakup or series of breakups signals climate change. On the other hand, it is quite obvious that every loss of flat ice subtracts from regional albedo, contributes to the absorption of solar energy, and should contribute to a regional increase in temperature.

But in a larger context, taking into consideration the history of navigation in the southern seas and the long term climatic evidence, it is a fairly reasonable tenet that the region has generally been warming. Magellan and Drake chose treacherous inter-island passages over what we presume was a previously ice-choked Antarctic sea. And 19th Century explorers sailed over open seas that 18th Century sealers and whalers had charted as continental ice. It is time for climatologists to return to the spirit of the Age of Exploration, become more the investigators and less the priests of doom or prescribers of salvation. --AGF 3/26/08

AP Science writer

AP's science writer, Seth Berenstein, is full of anecdotal evidence for global warming. In his latest report (3/19/08) he tells us that spring arrives on 3/20, at 0348 hours. One wonders how he arrives at this hour, for it is true in Greenland but nowhere else. But such are the calculations of science reporters: the only competent one I know of is Nigel Calder, who is a very vocal critic of the global warming craze. We're all still waiting for someone to put together a concise proof of the doom that awaits our continued CO2 pollution, but all we ever see is selective anecdotal evidence--citrus crop freezes are rarely mentioned, let alone explained.

--AGF