Ice on the move a warning of warming, or is it?greenspun.com : LUSENET : Grassroots Information Coordination Center (GICC) : One Thread
Ice on the move a warning of warming, or is it? By ROBERT LEE HOTZ Saturday 14 April 2001
When Douglas MacAyeal jumped out of a helicopter on to Iceberg B15A, he landed squarely on a central mystery of global warming and climate change.
Wedged against Ross Island, near McMurdo Station, the main United States National Science Foundation base in Antarctica, the berg is a leviathan of ice. It contains enough frozen fresh water to supply the US for three years. At the same time, B15A may be the smallest jigsaw piece in a global puzzle. The ice sheets of the world's remotest reaches are central to a renewed political debate over global warming and the carbon dioxide emissions widely considered responsible for it.
At every end of the earth, the ice is slowly stirring.
Major ice formations in Antarctica and the Arctic are thinning or breaking up. In the alpine highlands of Europe and the tropical ranges of South America and Africa, mountain glaciers are in full retreat.
From the snows of Kilimanjaro in Tanzania to the Quelccaya icecap of the Andes mountains in Peru, scientists see a world of ice in motion, shrinking, flexing, creeping unpredictably, almost like a living thing.
At a time when any scientific uncertainty about changing climate is politically charged, researchers are straining to understand the behavior of the ice sheets that cover one-tenth of the world, and contain three-quarters of its fresh water.
The more they learn, the more complicated it all seems to be.
Indeed, the world's icecaps are far more dynamic and complex than anyone would have guessed even a decade ago. A flood of new findings is framing a growing political clash over efforts to control carbon dioxide emissions and the burning of fossil fuels.
President George W. Bush recently reversed a campaign pledge to seek big reductions in US carbon dioxide emissions, and wants to abandon a landmark 1997 global-warming agreement, even as US Energy Department statisticians predict that levels of the so-called greenhouse gas will grow worldwide nearly 35 per cent by 2010.
Many scientists believe that the changes they see in the world's ice are the first symptoms of global warming, with potentially catastrophic consequences.
If the West Antarctic ice sheet melted, for example, it could raise the sea level by as much as six metres, enough to drown coastlines, cause higher tides, generate more powerful storm surges and change the ocean currents that help mediate the world's weather.
While earth's northern hemisphere has warmed about one degree Celsius since the Industrial Revolution began, there is equally compelling satellite data suggesting that the rest of the world is actually cooling.
Satellite measurements of temperatures in the troposphere, and independent measurements from balloons, show no evidence of significant global warming over the past 22 years, according to John Christy, the director of the Earth System Science Centre at the University of Alabama. .
Researchers readily acknowledge that it is still hard to distinguish between the effects of regional weather trends and the global effect of fundamental changes in the earth's atmosphere.
Depending on where they look, the picture changes. In some instances, it is all but impossible to distinguish between changes in the ice caused by rising temperatures today and those still unfolding from the global warming that ended the last Ice Age, almost 20,000 years ago.
Alaska, where the Columbia Glacier is rapidly retreating, has been warmer in recent decades. But Greenland, where the ice edge also is thinning, has been colder, said ice expert Joe McConnell, at the Desert Research Institute, Nevada.
In the same way, the Antarctic Peninsula has been warming steadily. But on the other side of the continent, Antarctica's Dry Valleys - the polar region's only ice-free areas - have been getting colder. At the South Pole, temperatures recently have dropped as low as minus 77 degrees, the coldest there in 40 years.
At the other end of the planet, the amount of sea ice in Arctic waters is shrinking annually, and the ice is as much as 40 per cent thinner.
Still, for all the change, no one knows precisely what to blame.
It could be higher temperatures or altered ocean currents - perhaps variations in cloud cover, solar radiation and atmospheric chemistry.
Greenhouse gases no doubt play an important role. It could be some subtle recipe of time and the natural rhythm of the ice itself.
"We are reasonably confident now that a whole lot of the things we have been getting excited about are not caused by global warming, and we aren't sure what they are," said glaciologist Richard Alley, of Pennsylvania State University, who is chairman of a panel on abrupt climate change at the National Academy of Sciences.
"The breakthrough in this decade is the ability to see these changes. They are revelations. The breakthrough in the next decade will be the ability to understand them."
They are, he said, "weird", a huge puzzle piece.
Mr MacAyeal approached B15A in the Ross Sea for the first time earlier this year aboard the US Coast Guard icebreaker Polar Sea.
A geophysicist from the University of Chicago, Mr MacAyeal is one of scores of glaciologists, geologists and other researchers funded by the US National Science Foundation who are systematically taking the scientific measure of the world's glaciers and icecaps.
Mr MacAyeal and his colleagues from the University of Wisconsin erected two weather stations and a set of global-positioning system transmitters on this forbidding raft of ice.
The instruments, working through a satellite relay, will allow them to watch the berg's unpredictable progress after they retreat to the central heating of their home laboratories.
They will track the iceberg for the next three years until eventually it breaks up and melts into the sea.
Some scientists believe that icebergs like B15A might be caused by warmer temperatures that make the ice shelves dangerously vulnerable to cracking.
If so, these unusually large icebergs would be disturbing symptoms of a global climate in flux. The theory is a persuasive notion. Overall, the decade of the 1990s is considered the warmest on record, and the temperature increases recorded in the 20th century are considered the highest of the past 1000 years.
Mr MacAyeal and his colleagues are confident that B15A, at least, has nothing to do with global warming.
Such icebergs appear routinely once or twice a century, he said.
In the case of B15A, the events that set things in motion may have started 500 years ago with an unexplained weakening that eventually developed into a fracture zone as the ice flowed toward the sea.
As the berg slowly broke free of the ice edge, it calved off six other immense pieces of ice.
"We think they come in flurries and avalanches," he said. "Whether the frequency is starting to change because of global warming, it is too soon to tell."
Only a few hundred kilometres to the north, an immense crack is growing along the Antarctic ice.
Within a year, NASA imaging experts said, the ice shelf there will fracture completely, calving another major iceberg into the Southern Ocean.
Lonnie Thompson, unlike Mr MacAyeal, studies ice along the equator, where ice fields linger only in the highest mountain nooks and crannies. Wherever he looks in the tropical highlands, he is certain that he can see global warming at work.
"These glaciers are very much like the canaries once used in coal mines," said Professor Thompson, of the Byrd Polar Research Centre, at Ohio State University. "They're an indicator of massive changes taking place, and a response to the changes in climate in the tropics."
Atop Tanzania's Mount Kilimanjaro, four-fifths of the vast ice field that covered the top of the highest mountain in Africa has disappeared in the past 80 years, he recently reported.
At least one-third of that ice field has disappeared in the last dozen years.
Speaking at a recent meeting of the American Association for the Advancement of Science, in San Francisco, Professor Thompson said that other researchers had documented similar ice losses.
An icecap on Mount Kenya has shrunk by 40 per cent since 1963. Two glaciers atop mountains in New Guinea are disappearing, and should be gone in a decade.
In Venezuela there are only two glaciers remaining where, in 1972, there were six. In another 10 years, those two are expected to be gone, as well.
In the ice fields of the Tibetan Plateau, Professor Thompson and his colleagues are convinced they have found evidence proving that rising temperatures are responsible.
If Professor Thompson is right, receding tropical glaciers are a harbinger of disastrous change to come, according to the UN-affiliated Intergovernmental Panel on Climate Change. The panel's most extreme projections say melting Antarctic ice could raise sea levels by as much as three metres over the next 1000 years.
Not so many years ago, researchers in Antarctica would have been quick to agree.
But the more they learn, the more they realise that the ice sheets of Antarctica are an unusually intricate puzzle.
Much of the attention has centred on the West Antarctic ice sheet. Unlike its larger counterpart, the East Antarctic ice sheet, it is not completely landlocked. Much of it rests on a marine basin and is drained by broad bands of ice flowing through the ice sheet to the sea, like streams threading through a river delta. Squeezed like toothpaste by the sheer weight of the continental blanket of ice, these flows normally creep through the gaps in the towering coastal mountain ranges that rim the polar plateau.
All told, they annually transport enough ice to bury Los Angeles. Any change in the behavior of the ice sheet was taken as a sign of instability and potential collapse.
And the more they looked, the more change they discovered.
One ice stream stopped moving 150 years ago. A second major ice stream has slowed by half in the past 40 years. A third ice stream, called the Pine Island Glacier, which drains much of the West Antarctic ice sheet, had inexplicably speeded up in the past five years, said Eric Rignot, of the Jet Propulsion Laboratory, and researchers at the British Antarctic Survey.
Researchers do not yet know why these ice streams are moving so differently. The ice streams can be affected by the underlying topography over which they flow, as well as by subtle effects of changing climate.
"We think this is the most unstable part of Antarctica," Mr Rignot said. "We see the ice thinning, but we are not sure why. The ice sheet may be doing its own thing. It may be driven by climate change. We don't know."
But researchers today are discovering that these massive ice sheets are more firmly anchored to the continent than previously believed.
Some of the changes they see now may be the result of the global warming that ended the last Ice Age. If that is the case, it is much too late to reverse them.
That slow pace of climate change highlights the problem scientists face trying to reconcile planetwide effects unfolding on a geologic time scale against a public attention span that measures time in election cycles and news breaks.
In Antarctica, they believe, the last Ice Age is only now coming to a close.
Researchers at the University of Colorado recently discovered that air temperatures in Antarctica rose significantly in just a few decades as the last Ice Age began to wane, the largest and most abrupt warming ever recorded in the southern hemisphere.
That temperature change is only now making its way to the bottom of the icecap, where it may be affecting how the ice flows.
The ice sheet might collapse in another 7000 years, researchers estimate.
In the same way, the behavior of the ice streams may be changing because of the flexible geometry of the immense ice sheet itself over the past 10,000 years, as stresses and strains naturally shift from one end to the other, according to ice expert Slawek Tulaczyk.
"People have matured in their understanding of how variable West Antarctica can be," said Julie Palais, who oversees a glaciology program. "We don't know the lifetime of this whole process. The time scales could be hundreds of years, or thousands of years."
But every year, researchers add to a growing understanding of this vast, intricate ecology of ice.
LOS ANGELES TIMES
This story was found at: http://www.theage.com.au/news/2001/04/14/FFX66RMTGLC.html
-- Martin Thompson (firstname.lastname@example.org), April 13, 2001