“Now, where the ice streams and the ice sheet in general came off the bedrock, and started floating in the Ross Sea— that was called the grounding line.”

“Ah,” said one of Fort’s friends. “Global warming?”

The geologist shook his head. “Our global warming has had very little effect on all this. It’s raised temperatures and sea levels a little bit, but if that was all that was happening it wouldn’t make much difference here. The problem is we’re still in the interglacial warming that began at the end of the last Ice Age, and that warming sends what we call a thermal pulse down through the polar ice sheets. That pulse has been moving down for eight thousand years. And the grounding line of the west ice sheet has been moving inland for eight thousand years. And now one of the under-ice volcanoes down there is erupting. A major eruption. About three months old now. The grounding line had already started to retreat at an accelerated rate some years ago, and it was very close to the volcano that’s erupted. It looks like the eruption has brought the grounding line right to the volcano, and now ocean water is running between the ice sheet and the bedrock, right into an active eruption. And so the ice sheet is breaking up. Lifting up, sliding out into the Ross Sea, and being carried away by currents.”

His listeners stared at the little inflatable globe. By this time they were over Patagonia. The geologist answered their questions, pointing out features on the globe as he did. This kind of thing had happened before, he told them, and more than once. West Antarctica had been ocean, dry land, or ice sheet, many times in the millions of years since tectonic movement had deposited that continent in that position. And there appeared to be several unstable points in the long-term temperature changes—”instability triggers,” he called them, causing massive changes in a matter of years. “This climatological stuff is practically instantaneous as far as geologists are concerned. Like, there’s good evidence in the Greenland ice sheet that one time we went from glacial to interglacial in three years.” The geologist shook his head.

“And these ice sheet breakups?” Fort asked.

“Well, we think they might go typically in a couple hundred years, which is still very fast, mind you. A trigger event. But this time the volcano eruption makes it much worse. Hey look, there’s the Banana Belt.”

He pointed down, and across Drake Strait they saw a narrow icy mountainous peninsula, pointing in the same direction as the coccyx of Tierra del Fuego.