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One thing they were trying was to slow the outflow glaciers off the Greenland ice cap. Antarctica and Greenland were the two meaningful reservoirs of ice left on the planet, and modelers were very hopeful that eastern Antarctica at least would hold fast through the heat peak into the hoped-for return to a colder atmosphere and ocean. If they could get the CO 2 down to 320 parts per million, and capture some of the methane, and temperatures therefore fell, and the ice cake on eastern Antarctica held, then the ocean would nevertheless stay high and warm for hundreds more years-but it would be a big success nonetheless. In fact if they failed to keep the East Antarctic ice, it wasn’t worth thinking about. So they needed to succeed. At some point, many were saying now, they were going to have to treat Earth like they were treating Mars and Venus, and whatever they lost by that would be too bad. Some said another little ice age was just what they needed; the billion or three likely deaths were not spoken of, but latent in the argument was the notion that fewer people wouldn’t hurt the situation either. Shock therapy-triage-people who liked to talk tough to make themselves look practical were full of this line.

So, Greenland was a much smaller ice cake than East Antarctica, but it was not insignificant. If it melted off (and it was a remnant of the previous ice age’s giant ice cap, located very far south for current conditions), it would mean another seven meters’ rise. That would ruin the adjusted new coastline civilization, so painfully fought for.

As with all ice sheets, it did not just melt; it slid in glaciers down into the sea, speeded by the lubrication of meltwater running under the ice, lifting the glaciers off their rock beds. It was the same in Antarctica, but while Antarctica’s ice slid down into the sea all the way round its circumference, so that there was nothing they could do about stopping it, Greenland was different. Its ice was mostly trapped within a high tub of encircling mountain ranges, and it could only slide down into the Atlantic through a few narrow gaps in the rock, like breaks in the edge of a bathtub. Through these gaps the lubricated glaciers poured at a speed of many meters a day, down U-valleys already smoothed for millennia, and when they hit the rising ocean, their snouts floated out over the terminal lips that often lay at the mouth of fjords, thus launching icebergs to sea more smoothly and swiftly than ever.

Early in the history of glaciology, researchers had noticed that one fast glacier in West Antarctica had suddenly slowed to a crawl. Investigations had found that the lubricating water underneath the ice had broken into some new channel and gone away, so that the immense weight of the glacier had thumped back onto the rock, causing it to stall. That now gave people ideas, and they were attempting to do something similar in Greenland by artificial means. They were testing several methods at one of the narrowest and fastest of the Greenland glaciers, the Helheim.

T he western coast of Greenland was rather reassuringly icy, Swan thought, given all that one heard about the big melt. Under their helicopter lay a skim of winter sea ice, breaking up into giant polygonal sheets of white on a black sea. There was a polar bear park on the north shores of Greenland and Ellesmere Island, she was told, where tabular bergs floated on the natural eddy or got herded there by long flexible booms pushed by solar-powered propellers. So the Arctic ice was not entirely gone, and it was really quite beautiful to see it below her, and also to see how black the ocean was, as unlike the blues of tropic seas as could be imagined. Black ocean, white ice. All the blues were in the sky and in melt ponds strewn everywhere on the exposed ice of the Greenland ice cap, held three kilometers above the ocean by jagged black ridgelines-the coastal range, the chewed edge of the bathtub, holding in place the inland plateau of ice. The whole situation was as clear as could be, viewed from a helicopter flying five kilometers up.

“Is that our glacier?” Swan asked.

“Yes.”

The pilot headed down toward a little red X marking a flat spot of rock on a ridge overlooking the glacier, several kilometers upstream from where it calved into the ocean. The flat spot as they descended turned out to be about twenty hectares, with room for the whole camp; the red X was giant. As they made their last descent the whole scene lay below them, a fantastic prospect of black spiny spires, white ice, blue sky, black sunbeaten water in the fjord.

Outside the helo it was stunningly cold. It made Swan gasp, and a bolt of fear shocked her: if one felt this kind of cold in space, it would mean a breakdown and imminent death. But here people were greeting her and laughing at her expression.