Warnings From Antarctica

A rift across the Larsen C Ice Shelf as seen from a NASA research aircraft in November. Credit John Sonntag/NASA

As the Trump administration dismantles the federal government’s efforts to respond to global warming, the natural world has come calling with a reminder: An iceberg the size of Delaware broke off Antarctica’s Larsen C ice shelf in recent days, yet another indication of the rapid change now occurring on the world’s iciest continent.

This is the third floating ice shelf in recent years in Antarctica’s Weddell Sea to fully or partly break up, the first two subverted by warming ocean waters and air temperatures. The Larsen A broke up in 1995. Seven years later, after months of unusually warm temperatures, the Rhode Island-size Larsen B shelf became riddled with meltwater ponds, then fell apart virtually overnight, shattering into millions of pieces. Now a 120-mile-long chunk of the Larsen C has calved, forming one of the largest icebergs ever observed.

The ice shelf has been floating in the frigid waters on the eastern side of the Antarctic Peninsula for at least 10,000 years. It was in the Weddell Sea that Ernest Shackleton’s ship, Endurance, became trapped in ice in 1915, forcing him and his crew to abandon ship in an epic battle for survival. Now a region that not long ago saw only snow and ice is experiencing — at least in its northern reaches — rain in summer.

Talk to scientists who have worked in the Arctic, Antarctic or the world’s glacial zones for decades, and what they keep coming back to is that they have witnessed monumental physical changes in these once-frozen regions within their professional lifetimes.

Last year the Arctic experienced exceptionally warm weather that has continued into 2017, as sea ice shrinks to near-record lows. Temperatures last fall were as much as 36 degrees Fahrenheit above normal over parts of the Arctic. Both the extent and thickness of Arctic summer sea ice have decreased sharply since satellite remote sensing began in 1979.

Few climate scientists doubt that within a decade or two the cap of ice that has covered the Arctic Ocean for tens of thousands of years, acting as a giant planetary air conditioner, will largely disappear in summer, replaced by heat-absorbing open ocean. One more physical feature that has characterized our planet for ages will have vanished in a matter of decades.

Greenland’s ice sheet, the planet’s second largest after Antarctica, is melting at an alarming rate, losing an estimated 90 cubic miles of ice a year. The melt water that ends up in the ocean is raising sea levels. And then there are the countless glaciers in the Alps, Andes, Himalayas, Rockies and Tibetan Plateau, all melting as our unceasing carbon dioxide emissions — a staggering 35 to 40 billion tons a year — trap more and more heat.

Icebergs routinely break off Antarctica’s glaciers and ice shelves, although rarely are they as large as this week’s huge calving. Scientists are debating exactly how much climate change is responsible for the creation of this latest iceberg. But given regional warming and the previous losses of Larsen A and B, some leading polar ice experts say this most recent event is a sign of the Larsen C Ice Shelf’s growing instability. Because ice shelves float on the ocean, their disintegration does not increase sea levels. But the ice shelves hold back land-based glaciers, and when the shelves go, the glaciers often rush into the sea, raising the level of the oceans.

While the destabilization of the Larsen C Ice Shelf is certainly worrying, it pales in comparison with the threat from the increasing instability of the glaciers and ice shelves holding back the enormous West Antarctic Ice Sheet. If much of that ice sheet thaws and slides into the sea this century or next, global sea levels could rise by up to 17 feet.

Nearly 40 years ago, when global warming had yet to become an urgent issue, even among the scientific establishment, The Ohio State University glaciologist John H. Mercer foresaw these staggering changes. Writing in the journal Nature, he warned: “If present trends in fossil fuel consumption continue… a critical level of warmth will have been passed in high southern latitudes 50 years from now, and deglaciation of West Antarctica will be imminent or in progress.”

One sign of a dangerous warming trend, he predicted, would be the breakup of floating ice shelves on both coasts of the Antarctic Peninsula, the warmest part of the coldest continent.

Like many scholars who have tracked the pace of climate change, Dr. Mercer turned out to have underestimated just how rapidly our fossil fuel emissions would transform the face of the planet. Since Dr. Mercer wrote those words in 1978, steadily rising air and ocean temperatures have indeed led to the full or partial breakup of eight ice shelves along the Antarctic Peninsula, including the Larsen ice shelves.

Across the globe, such changes have accelerated dramatically in just two generations. What upheaval global warming will bring to the next several generations — if we don’t sharply rein in emissions of carbon dioxide — is almost impossible to imagine.

Fen Montaigne is the senior editor at Yale Environment 360 and the author of Fraser’s Penguins: A Journey to the Future in Antarctica.

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