"Another climate-driven disaster in the making that could dwarf even the shutting down of the Gulf Stream is the possibility that the Western Antarctic Ice Sheet might break off, which could happen at any time and would cause sea level to rise five to ten meters. "WAIS [as the people who are watching it refer to it] has not budged since warming began, but when it does start to slip, it will happen very fast, and a very large amount of ice will find itself in the ocean, and you can say goodbye to the Maldives and Bangladesh," Elliot Norse told me. "The break-off will be a non-linear response to linear input. Nature works most often by the straw that breaks the camel principle, or as Malcolm X said of Kennedy's assassination, by the chickens coming home to roost."

        I contacted John Behrendt, an expert on  WAIS and a colleague of Kevin Trenberth at the NARC in Boulder. He began by explaining the difference between an ice shelf and an ice sheet. The Ross Ice Shelf is already floating. It freezes into pack ice in winter and is open in the summer. WAIS, however, is grounded, attached to the Ross Sea's continental shelf, a marine-bed ice sheet that has been there for the last 20 or 30 million years, flowing off at its edge and being remade by snow. It is a huge chunk of snow and ice, 500 miles  long by 500 wide and about 9,000 feet thick (12,000 feet at its thickest point), about half of which is below sea level.  Six ice streams flow beneath it, and it is already sliding on mud, "like syrup poured on a table," Behrendt explained, toward the Ross Ice Shelf and the open water beyond at the rate of 1200 feet a year. Global warming or the active volcanos under the sheet, could cause it to deglaciate, to break off and collapse, as happened with the Laurentide Ice Sheet a hundred thousand years ago and is happening now with the glaciers at the Glacier Bay National Park, Alaska, which are rapidly breaking off and slipping into the sea. "If WAIS deglaciates and surges out into the sea, sea level will equalize all over the earth at about six meters, or twenty feet, higher than it is now," Behrendt estimated. "But it is controversial that it will even do this," he cautioned, "and it would take several centuries at least to effect the rise. It's the snow and ice that is above sea level that will break up into icebergs that will gradually melt and cause the rise."  Whew, I thought. There's time on this one. Norse had made it sound as if the rise could happen in a quickly as a year.

      Behrendt suggested I talk to his colleague, Mark Meier, an authority on sea-level rise, for a second opinion. Meier told me that in the last 100 years the sea has been rising by about two millimeters a year-- "more than in the past, and it will rise by more in the future. One third is due to the heating and expansion of the mix zone, the top hunded meters, one third is due to glaciers melting, and the other third is from what ? Tk.". As far as WAIS was concerned, he confirmed that "it's the top 4500 feet that matters,  and the expected sea level rise from their melting cannot happen quickly. It will take hundreds of years. But already," he said, "global warming is causing many of the ice shelves that are already floating to break up and drift out to sea as icebergs. This will relieve some of the back pressure on the ice streams that feed the shelves and will draw down the ice sheets from the [Antarctic] continent. The mid-range estimate for sea-level rise over the next century is twenty inches."

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