TASIILAQ, Greenland — 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 seven 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 three 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 six 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 three 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.
In the United States, parts of the East Coast and Gulf Coast would be hit hard. In New York, coastal flooding could become routine, with large parts of Queens and Brooklyn especially vulnerable. About 15 percent of the urbanized land in the Miami region could be inundated. The ocean could encroach more than a mile inland in parts of North Carolina.
Abroad, some of the world’s great cities — London, Cairo, Bangkok, Venice and Shanghai among them — would be critically endangered by a three-foot rise in the sea.
Climate scientists readily admit that the three-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 five 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 three-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.
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 three-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 dyingand many other changes are afoot that most climate scientists attribute to global warming. (NYT)
