When you think about it, it's not surprising that Antarctica seems to be breaking apart. Our old granite planet has been warming up! Examples of remarkable warmth during just the past few months include, some lakes remaining unfrozen in New York for the first time in memory, cherry blossoms in Japan having their earliest blooming date ever recorded, sled races being cancelled in the upper Mid West because of too little snow, wildfires threatening Sydney, Australia, and the list goes on and on. In fact, the four warmest years on record, world-wide, have occurred since 1990.

On the other hand, it may not be as steamy as it seems. A few months back, snow fell and even accumulated in Athens, Greece (an unusual occurrence), temperatures plummeted to -80 degrees F below zero in some Siberian villages, and Washington's cherry blossoms are blooming about their normal time. There may not be a need to abandon the coasts and head for the hills just yet.

In the past two decades or so, a number of huge ice chunks have snapped off of glaciers in the Antarctic. Two years ago, a Delaware-sized piece fell off of the Ross Ice Shelf. Tabular icebergs collapsing into the sea in recent years have raised concerns that global warming is now causing the West Antarctic Ice Sheet to give way, which could lift the level of the sea by 20 feet (6.8 m) during the next century. This would have dire consequences for the millions of people around the globe who live tight against the sea.

This most recent episode of ice disintegration, while it happened in Antarctica, actually occurred north of the Antarctic Circle. A portion of the Larsen Ice Shelf (Larsen B), which used to sit at about 66 degrees S latitude, shattered and separated from the eastern side of the Antarctic Peninsula earlier this month. It's believed that this was the largest such collapse in at least 30 years. It's estimated that a total of approximately 1,250 square miles (3,250 square km) of the Larsen Ice Shelf, about the size of the state of Rhode Island, has slipped into the Weddell Sea since early February. This fractured ice has resulted in the formation of thousands of icebergs.

The Larsen has been heavily monitored for the past couple of years since there were telltale signs that something was amiss. Field studies and satellite observations indicated that the ice shelf's flow rate had increased dramatically - a precursor to or even a suggestion of instability. Ice shelves are basically thick plates of floating ice fed by glaciers. Glacial ice creeps down from areas of higher elevation towards the sea, and upon reaching the sea, it can become anchored (grounded) at the sea bed, at which time it's fairly stable. Ice streams (areas where ice is moving relatively quickly) supply ice to the ice shelf, which continues to spread outward across the sea, forming a floating ice mass that can be thousands of feet in thickness. The Larsen B shelf was 880 ft (220 m) thick, and it may have been in existence since the end of the last major glaciation, about 12,000 years ago.

If something causes the discharge rate of ice to change, a stable ice shelf can suddenly become unstable. In the case of the Larsen, it's thought that warming temperatures, both on the surface of the ice and in deep water at the bottom of the shelf, have been large responsible for its demise. Since the 1940s, over the Antarctic Peninsula, the rate of warming has been about 0.5 degrees C per decade. In the last quarter century, seven ice shelves along the peninsula have been reduced in size by approximately 5,200 sq mi (13,500 sq. km).

If all of the world's ice shelves were to collapse into the sea in the next year or so, with no further consequences, sea level wouldn't be any different then it is now. Since ice shelves are already floating, they're in equilibrium with the sea. For the same reason, when ice cubes in your favorite beverage melt, the level of the liquid in you glass doesn't change. However, if the ice shelves disappear, glacial ice that's not now floating could pour into the sea, which would then raise the sea level. Fortunately, because the Larsen Ice Shelf is anchored to a peninsula rather than the bulk of the continent, there's not a massive ice sheet now poised to rush toward the Weddell Sea.

The collapse of the Larsen B sounds like a song Gordon Lightfoot should write - if so this might help him.

the legend lives on from mariners on down bout the big shelf called Larsen B
the ice might crack, fracture and moan but could never fall into the sea
but now it's gone and glaciologists groan oh where be the Larsen B

Well, maybe not. Anyway, there's apparently no direct link between global warming and the collapse of the Larsen B. It seems rather that localized warming in the Antarctic Peninsula triggered the collapse. There's no real threat to the South Pole melting. The temperature at the South Pole has only been above 0 degrees F (- 18 degrees C) less than a hand full of occasions since it was first instrumented in the late 1950s. Even if temperatures were to increase at the pole several degrees each year, it would be a long while before meltwater appeared at the surface. Interestingly, data from weather stations over the rest of Antarctica indicate that air temperatures have been slightly cooler than normal during the past decade. In fact, there's evidence that while the edges of both the Greenland and Antarctic ice sheets have been thinning for some time, the centers of both these ice sheets have been gaining mass - snow has been accumulating at a faster pace than it has been melting or sublimating. The bottom line is that the jury is still out as to whether or not ice shelves in Antarctica will continue to tumble into the sea.