Greeland glaciers show alarming rate of ice melt
Many scientists now say that sea level is likely to rise perhaps three feet by 2100
With a tense pilot gripping the stick, the helicopter hovered above the water, a red speck of machinery lost in a wilderness of rock and ice. To the right, a great fjord stretched toward the sea, choked with icebergs. To the left loomed one of the immense glaciers that bring ice from the top of the Greenland ice sheet and dump it into the ocean.
Hanging out the sides of the craft, two scientists sent a measuring device plunging into the water, between ice floes. Near the bottom, it reported a temperature of 40 degrees. It was the latest in a string of troubling measurements showing that the water was warm enough to melt glaciers rapidly from below.
“That’s the highest we’ve seen this far up the fjord,” said one of the scientists, Fiammetta Straneo.
The temperature reading was a new scrap of information in the effort to answer one of the most urgent — and most widely debated — questions facing humanity: How fast is the world’s ice going to melt?
Scientists long believed that the collapse of the gigantic ice sheets in Greenland and Antarctica would take thousands of years, with sea level possibly rising as little as 7 inches in this century, about the same amount as in the 20th century.
But researchers have recently been startled to see big changes unfold in both Greenland and Antarctica.
As a result of recent calculations that take the changes into account, many scientists now say that sea level is likely to rise perhaps 3 feet by 2100 — an increase that, should it come to pass, would pose a threat to coastal regions the world over.
And the calculations suggest that the rise could conceivably exceed 6 feet, which would put thousands of square miles of the American coastline under water and would probably displace tens of millions of people in Asia.
The scientists say that a rise of even 3 feet would inundate low-lying lands in many countries, rendering some areas uninhabitable. It would cause coastal flooding of the sort that now happens once or twice a century to occur every few years. It would cause much faster erosion of beaches, barrier islands and marshes. It would contaminate fresh water supplies with salt.
Some of the world’s great cities — London, Cairo, Bangkok, Venice and Shanghai among them — would be critically endangered by a 3-foot rise in the sea.
Climate scientists readily admit that the 3-foot estimate could be wrong. Their understanding of the changes going on in the world’s land ice is still primitive. But, they say, it could just as easily be an underestimate as an overestimate. One of the deans of American coastal studies, Orrin H Pilkey of Duke University, is advising coastal communities to plan for a rise of at least 5 feet by 2100.
“I think we need immediately to begin thinking about our coastal cities — how are we going to protect them?” said John A Church, an Australian scientist who is a leading expert on sea level. “We can’t afford to protect everything. We will have to abandon some areas.”
Sea-level rise has been a particularly contentious element in the debate over global warming. One published estimate suggested the threat was so dire that sea level could rise as much as 15 feet in this century. Some of the recent work that produced the 3-foot projection was carried out specifically to counter more extreme calculations.
Global warming skeptics, on the other hand, contend that any changes occurring in the ice sheets are probably due to natural climate variability, not to greenhouse gases released by humans.
Skeptical legislators
Such doubts have been a major factor in the American political debate over global warming, stalling efforts by Democrats and the Obama administration to pass legislation that would curb emissions of heat-trapping gases. Similar legislative efforts are likely to receive even less support in the new Congress, with many newly elected legislators openly skeptical about climate change.
A large majority of climate scientists argue that heat-trapping gases are almost certainly playing a role in what is happening to the world’s land ice. They add that the lack of policies to limit emissions is raising the risk that the ice will go into an irreversible decline before this century is out, a development that would eventually make a 3-foot rise in the sea look trivial.
Melting ice is by no means the only sign that the earth is warming. Thermometers on land, in the sea and aboard satellites show warming. Heat waves, flash floods and other extreme weather events are increasing. Plants are blooming earlier, coral reefs are dying and many other changes are afoot that most climate scientists attribute to global warming.
The missing information makes it impossible for scientists to be sure how serious the situation is. “As a scientist, you have to stick to what you know and what the evidence suggests,” said Gordon Hamilton, one of the researchers in the helicopter. “But the things I’ve seen in Greenland in the last five years are alarming. We see these ice sheets changing literally overnight.”
Two seismologists, Meredith Nettles and Goran Ekstrom of Columbia University, discovered a few years ago that unusual earthquakes were emanating from the Greenland glaciers as they dumped the extra ice into the sea. “It’s remarkable that an iceberg can do this, but when that loss of ice occurs, it does generate a signal that sets up a vibration that you can record all across the globe,” Nettles said.
Analysing past records, they discovered that these quakes had increased severalfold from the level of the early 1990s, a sign of how fast the ice is changing.
Satellite and other measurements suggest that through the 1990s, Greenland was gaining about as much ice through snowfall as it lost to the sea every year. But since then, the warmer water has invaded the fjords, and air temperatures in Greenland have increased markedly. The overall loss of ice seems to be accelerating, an ominous sign given that the island contains enough ice to raise global sea levels by more than 20 feet.
Strictly speaking, scientists have not proved that human-induced global warming is the cause of the changes. They are mindful that the climate in the Arctic undergoes big natural variations. In the 1920s and '30s, for instance, a warm spell caused many glaciers to retreat.
John R Christy, a climatologist at the University of Alabama in Huntsville who is often critical of mainstream climate science, said he suspected that the changes in Greenland were linked to this natural variability, and added that he doubted that the pace would accelerate as much as his colleagues feared.
For high predictions of sea-level rise to be correct, “some big chunks of the Greenland ice sheet are going to have to melt, and they’re just not melting that way right now,” Christy said.
Yet other scientists say that the recent changes in Greenland appear more pervasive than those of the early 20th century, and that they are occurring at the same time that air and ocean temperatures are warming, and ice melt is accelerating, throughout much of the world.
