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Rafael Norma · 14-noviembre-2010, 04:55

Re: que se lso traduzca su abuelita....

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The consequence is that researchers lack elementary information. They have been unable even to measure the water temperature near some of the most important ice on the planet, much less to figure out if that water is warming over time. Vital satellites have not been replaced in a timely way, so that American scientists are losing some of their capability to watch the ice from space.

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.”

Dodging Icebergs

In the brilliant sunshine of a late summer day in southeastern Greenland, the pilot at the controls of the red helicopter, Morgan Goransson, dropped low toward the water. He used the downdraft from his rotor to clear ice from the surface of Sermilik Fjord.

The frigid waters were only 30 feet below, so any mechanical problem would have sent the chopper plunging into the sea. “It is so dangerous,” Mr. Goransson said later that night, over a fish dinner.

Taking the temperature of waters near the ice sheet is essential if scientists are to make sense of what is happening in Greenland. But it is a complex and risky business.

The two scientists — Dr. Straneo, of the Woods Hole Oceanographic Institution in Massachusetts, and Dr. Hamilton, of the University of Maine — are part of a larger team that has been traveling here every summer with financing from the National Science Foundation, the federal agency that sponsors much of the nation’s most important research. Not only do they remove the doors of helicopters and lean over icy fjords to get their readings, but they dodge huge icebergs in tiny boats and traipse over glaciers scarred by crevasses that could swallow large buildings.

The reading that the scientists obtained a few weeks ago, of 40 degrees near the bottom of the fjord, fit a broader pattern that researchers have been detecting in the past few years.

Water that originated far to the south, in warmer parts of the Atlantic Ocean, is flushing into Greenland’s fjords at a brisk pace. Scientists suspect that as it melts the ice from beneath, the warm water is loosening the connection of the glaciers to the ground and to nearby rock.

The effect has been something like popping a Champagne cork, allowing the glaciers to move faster and dump more ice into the ocean. Within the past decade, the flow rate of many of Greenland’s biggest glaciers has doubled or tripled. Some of them have eventually slowed back down, but rarely have they returned to their speed of the 1990s.

Two seismologists, Meredith Nettles and Göran Ekström 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,” Dr. Nettles said in an interview in Greenland.

Analyzing 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,” Dr. Christy said.

Rafael Norma · 14-noviembre-2010, 04:55

Re: que se lso traduzca su abuelita....

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.

Helheim Glacier, which terminates in Sermilik Fjord, is one of a group of glaciers in southeastern Greenland that have shown especially big changes.

On a recent day, the red helicopter landed on a rocky outcrop above the glacier, a flowing river of ice about 25 miles long and nearly four miles wide. On the side of the canyon, Dr. Hamilton pointed toward a band of light-colored rock.
Temperature Rising

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It was, in essence, a bathtub ring.

Something caused the glacier, one of Greenland’s largest, to speed up sharply in the middle of the last decade, and it spit so much ice into the ocean that it thinned by some 300 feet in a few years. A part of the canyon that was once shielded from the sun by ice was thus left exposed.

The glacier has behaved erratically ever since, and with variations, that pattern is being repeated all over Greenland. “All these changes are happening at a far faster pace than we would have ever predicted from our conventional theories,” Dr. Hamilton said.

A few days after the helicopter trip, an old Greenlandic freighter nudged its way gingerly up Sermilik Fjord, which was so choked with ice that the boat had to stop well short of its goal. “You have to be flexible to work out here,” said the leader of the team that day, Dr. Straneo of Woods Hole.

Soon she was barking orders, and her team swung into motion. A cold, Arctic drizzle fell on the boat and the people. Off the port side in a rickety skiff, David Sutherland, a young scientist at the University of Washington, tossed a floating buoy, carrying a string of instruments, into the water, and an anchor snatched it below the surface. Over the next year, it will measure temperature, currents and other factors in the fjord.

Dr. Sutherland climbed back aboard the freighter with cold, wet feet. As the boat headed back to port, it passed icebergs the size of city blocks, chunks of the Greenland ice sheet bound for the open sea.

An Ocean in Flux

The strongest reason to think that the level of the sea could undergo big changes in the future is that it has done so in the past.

With the waxing and waning of ice ages, driven by wobbles in the earth’s orbit, sea level has varied by hundreds of feet, with shorelines moving many miles in either direction. “We’re used to the shoreline being fixed, and it’s not,” said Robin E. Bell, a scientist at the Lamont-Doherty Earth Observatory of Columbia University.

But at all times in the past, when the shoreline migrated, humans either had not evolved yet or consisted of primitive bands of hunter-gatherers who could readily move. By the middle of this century, a projected nine billion people will inhabit the planet, with many millions of them living within a few feet of sea level.

To a majority of climate scientists, the question is not whether the earth’s land ice will melt in response to the greenhouse gases those people are generating, but whether it will happen too fast for society to adjust.

Recent research suggests that the volume of the ocean may have been stable for thousands of years as human civilization has developed. But it began to rise in the 19th century, around the same time that advanced countries began to burn large amounts of coal and oil.

The sea has risen about eight inches since then, on average. That sounds small, but on a gently sloping shoreline, such an increase is enough to cause substantial erosion unless people intervene. Governments have spent billions in recent decades pumping sand onto disappearing beaches and trying to stave off the loss of coastal wetlands.

Scientists have been struggling for years to figure out if a similar pace of sea-level rise is likely to continue in this century — or whether it will accelerate. In its last big report, in 2007, the United Nations group that assesses climate science, the Intergovernmental Panel on Climate Change, said that sea level would rise at least seven more inches, and might rise as much as two feet, in the 21st century.

But the group warned that these estimates did not fully incorporate “ice dynamics,” the possibility that the world’s big ice sheets, as well as its thousands of smaller glaciers and ice caps, would start spitting ice into the ocean at a much faster rate than it could melt on land. Scientific understanding of this prospect was so poor, the climate panel said, that no meaningful upper limit could be put on the potential rise of sea level.

That report prompted fresh attempts by scientists to calculate the effect of ice dynamics, leading to the recent, revised projections of sea-level rise.

Satellite evidence suggests that the rise of the sea accelerated late in the 20th century, so that the level is now increasing a little over an inch per decade, on average — about a foot per century. Increased melting of land ice appears to be a major factor. Another is that most of the extra heat being trapped by human greenhouse emissions is going not to warm the atmosphere but to warm the ocean, and as it warms, the water expands.

With the study of the world’s land ice still in its early stages, scientists have lately been trying crude methods to figure out how much the pace might accelerate in coming decades.

One approach, pioneered by a German climate researcher named Stefan Rahmstorf, entails looking at the past relationship between the temperature of the earth and sea level, then making projections. Another, developed by a University of Colorado glaciologist named Tad Pfeffer, involves calculations about how fast the glaciers, if they keep speeding up, might be able to dump ice into the sea.

Those two methods yield approximately the same answer: that sea level could rise by 2 1/2 to 6 1/2 feet between now and 2100. A developing consensus among climate scientists holds that the best estimate is a little over three feet.