Icy Clues to Climate of Future

Working poles apart--on the crystal crown of the Arctic icecap and on the ice domes of Antarctica--researchers are coming to grips with Earth’s frozen past in order to predict its future.

For scientists trying to learn how global warming may affect the climate’s course, understanding the character and chemistry of the ice and snow at the planet’s extremities has taken on an unusual urgency.

The information they seek could be critical to efforts to curb the burning of fossil fuels and industrial emissions. To stave off global warming, world leaders are preparing to meet in November to prepare the first international controls on emissions of greenhouse gases such as carbon dioxide.

Recent studies of prehistoric ice in Greenland suggest that the world’s climate may be balanced on a knife’s edge--subject, with almost no warning, to potentially devastating temperature swings causing disasters ranging from floods to crop failures.

Based on their analysis of ancient ice, some scientists are concerned that any human-made changes in the delicate balance of the atmosphere could trigger quick, catastrophic climate changes that could take as little as a year or two.

In drilling completed here four years ago, researchers funded by the National Science Foundation and the European Science Foundation have tapped an archive of ice and snow that records a quarter-million years of winter and summer seasons, as layer upon layer of prehistoric snow was compressed in a frigid parfait of time.

Each core is a diagnostic probe of the past--a cylinder up to two miles long trapping information about conditions in the atmosphere that prevailed when the crystals first formed as falling snow.

These cores offer the clearest picture so far of how the weather has changed. They are the benchmark by which the history of the planet’s climate is measured and its future mapped.

They reveal hints that the effect of any global warming might, paradoxically, trigger cold weather severe enough to cause a global winter lasting years. The shift from the warm contemporary climate to an ice age could take less than a human lifetime.

“It raises the possibility that, by putting out greenhouse gases, humans may make the climate unstable and plunge us in as little as a decade into severe cold periods,” said Kendrick Taylor at the Nevada Desert Research Institute, chief scientist for a consortium of 15 universities using ancient ice cores to investigate climate.

But the ice does not yield its secrets so readily. Although it offers tantalizing hints about the climatic past, any conclusions are still obscured by the convoluted chemistry of frozen snow and gas.

So little is known about the processes by which snow and the air it traps are preserved as ice that some researchers worry that scientists may be misreading the past.

Now--as spring comes earlier each year throughout the northern hemisphere, alpine glaciers recede and other signs of climate change accumulate--researchers are trying to assess the accuracy of the evidence drawn from the world’s ancient ice.

The scientific uncertainties are focused here at Summit, the center of the Greenland icecap.

Testament to the Past

Ordinarily, there is no more perfect symbol than a snowflake for the impermanence and inaccessibility of the past--each crystal unique when it falls, quick to melt, irrecoverable when it evaporates.

Yet at Summit, ice and snow are a monument to the persistence of the past.

The ice dome is almost two miles thick and, at bedrock, almost 250,000 years old. It is so heavy the island has settled 2,000 feet under its weight, so forbidding that only scientists and lost seabirds make their way so far onto this central plateau.

The wind gusts across a featureless plain of ice that stretches for 810,000 square miles before it puddles in glacial whorls and pressure ridges against the rim of coastal mountains. The white of the ice sheet is broken by patches of cosmic dust, swept up over the eons by the movement of glaciers and collected as silt in blue meltwater pools.

These reaches of ice, which for centuries served only to isolate Greenland from the mainstream of history, have made this remote Arctic region--Earth’s oldest and largest island--the focus of international scientific attention.

“It is a giant laboratory here,” said Mary Albert, a research engineer from the U.S. Army Cold Regions Research and Engineering Laboratory in Hanover, N.H.

To researchers, the Arctic snowflakes--and the minute traces of chemicals, dust and isotopes they contain--are as valuable in their own way as scrapings of soil from Mars.

Trying his best not to breathe on the new snow, geochemist Jack Dibbs gathered three jars of crystals for scientists at the University of New Hampshire, where he is an assistant research professor, and three more for French climate researchers.

In a related experiment, Dibbs collected two quarts of air at the same spot, filtered them and chilled them to 148 degrees below zero Fahrenheit. Sealed in a pressurized canister, the air would be shipped 3,500 miles to UC Irvine, where environmental scientists would analyze it for about 80 trace chemicals.

Nearby, a spindly yardarm covered with electronic sensors stuck up from the ice field. The device automatically relays wind speed, barometric pressure and other snow soundings through an orbiting satellite to researchers in the United States.

When transformed into annual layers of ice, the snow becomes a diary of conditions around the world.

Every year, new snow captures the dust, chemicals and any pollution in the air, then concentrates them as the snow turns into ice under the weight of more snowfalls.

Oxygen and hydrogen isotopes in the ice track the rise and fall of seasonal temperatures. Layers of dust and ash reveal wind patterns and volcanic eruptions. Gas bubbles record concentrations of greenhouse gases. Traces of salt are the residue of ocean storms. Ammonium is a record of distant forest fires. Methane is one measure of distant rainfall and the strength of annual monsoons. Calcium hints at the extent of the world’s deserts, while beryllium levels indicate changes in solar radiation.

Each new layer of fresh snow typically is 90% to 95% trapped air, but no one knows how pure that air remains as other layers of snow build up over it.

If the air in each snow layer can mix--diluting or enriching its chemical composition as it turns into ice--then the cores may not be as accurate a record of seasonal conditions as many scientists believe.

Consequently, researchers are trying to better understand how the snow forms, how quickly it accumulates and what really happens as it is transformed into ice.

So scientists are honing a sophisticated sense of snow--how it breathes as the barometric pressure varies, how gases diffuse deep into its drifts, how its crystals change with temperature, and how accurately it records the history of the world’s climate.

“We are trying to understand the relationship between the composition of the air and the composition of the snow,” Dibbs said. “You need to know if the trend you see in the ice is real.”

So pressing is the need for new information that for the first time a team of four National Science Foundation researchers will spend the winter on the Greenland icecap to monitor the extreme conditions of the Arctic night, when much of the snow accumulates. Temperatures will reach 65 below and any automated electronic sensors simply will freeze.

To better understand the entire icecap, the science foundation this fall will allow an icebreaker to freeze in place for a year north of Prudhoe Bay in the vast canopy of pack ice--about the size of the United States--that seals off the Arctic Ocean every winter.

Under any other circumstances, this mission would be the stuff of a maritime disaster--an icebreaker helpless in a crushing vise of ice--but the ship will be a floating science station for about 50 researchers throughout the Arctic winter in what is believed to be the largest and most ambitious experiment conducted by the federal government in the seas surrounding the North Pole.

At the same time, scientists are hauling drill rigs into the highlands of Tibet and wherever else linger the vestiges of ancient glaciers that once sprawled across the continents.

Drilling programs also have been launched in Greenland and Antarctica this year to confirm the picture of the climate based on the earlier ice studies--all in the belief that anyone attempting to understand how human activities may alter the climate must first understand the past.

Trail Leads to Greenland

Until the end of the Cold War, Greenland, a sparsely populated island fringed by a narrow tonsure of habitable tundra, was isolated as much by military secrecy as by its forbidding climate.

While its strategic importance may be dwindling, there is growing scientific appreciation of its icecap.

“Several of the most reputable climate models have suggested that the Arctic is going to feel any global climate change sooner than anywhere else on Earth,” said Michael Ledbetter, director of the National Science Foundation arctic system science program, which funds the Greenland projects. “But without long-term knowledge of the Arctic, we stand a real chance of misinterpreting a very large change as a global warming change when it may be part of a natural cycle,” he said. A misunderstanding could result in needless environmental controls or, conversely, government action too late to arrest potentially devastating climate change.

At the edge of the most densely populated portions of the northern hemisphere, the Greenland ice sheet plays a crucial role in shaping the world’s weather, matched perhaps only by Antarctica in the Southern Hemisphere.

Scientists from 22 universities and research centers have been poring over the fine print revealed in these Summit ice records.

Even under the undisturbed conditions of past eons, the Greenland ice reveals, the world’s climate has been mercurial. Researchers discovered an erratic, “flickering climate” during the past several hundred thousand years, of sudden swings from warm to cold and back again in as little as a few decades.

Based on an analysis of oxygen isotopes in the Greenland ice, European and U.S. researchers have concluded that during the last ice age the ancient climate may have fluctuated wildly, with average annual temperatures rising as much as 11 degrees in as little as five to 20 years, only to slide back into a deep chill lasting thousands of years.

Scientists discovered evidence of two dozen abrupt shifts between 15,000 and 110,000 years ago, when temperatures rose suddenly and snowfall and methane levels in the air doubled. Wind-blown sea salt and dust increased tenfold, indicating more powerful storms and growing world deserts. The transition about 10,000 years ago from the last ice age to the present warm period may have taken less than a human lifetime, not the centuries of gradual warming that most scientists had once assumed.

In research made public this year, scientists found that an ice core taken from a 500,000-year-old glacier on the Tibetan Plateau in western China supports the idea that the climate is more unstable than believed.

Temperatures rose almost to modern levels at least four times during the last glacial period in areas around the equator, scientists at Ohio State University reported. More recently--15,000 to 33,000 years ago--there were about 100 “abrupt climate changes,” about every 200 years, they determined.

Until now, many researchers had assumed that the climate in the tropics and subtropics has been fairly stable, even when the polar regions showed climate shifts.

And when University of New Hampshire researchers recently looked at the climate changes that heralded the beginning of the modern era about 8,000 years ago--as continental ice sheets made their final retreat--they discovered that the changes appeared to begin in Greenland.

But in the eon since--the period in which humanity developed cities and the trappings of settled civilization--the climate has been unusually temperate.

The one part of the past scientists are most anxious to investigate in detail is an ancient warm period that most closely resembles conditions today. But that is the one area in which some of the Greenland ice cores do not agree.

“Many people are thinking about global warming, and this period could give some indication of what to expect,” said Sepp Kipfstuhl, a glaciologist at the Alfred Wegner Institute in Germany.

The period--called the Emean period--occurred about 110,000 years ago and was about four degrees warmer than today--so tropical, in fact, that hippos splashed in the Danube.

Yet in the ice records, scientists found unexpected evidence of eight abrupt temperature drops during this period. Average temperatures appeared to drop as much as 18 degrees in a decade.

Analysis of the ice suggests that the Emean may have ended with a gradual global warming that triggered two dramatic decades-long pulses of chill temperatures, which in turn culminated in thousands of years of glacial cold.

The effect is more logical than it sounds. As the climate warms initially, scientists explain, there is more moisture in the air; therefore, more snow falls each winter. More snow builds up as glacial ice, which in turn reflects more of the sun’s heat, lowering global temperatures dramatically. If the glaciers spread over enough of the earth, the cycle can quickly refrigerate the planet.

The problem is that the Emean period only shows up in the tail end of the cores, where the ice was drawn from a depth of about 1.5 miles. There, the annual ice layers are distorted, folded and even broken by the jagged surface of the bedrock. Distorted in different ways, the cores do not agree with each other.

“Either one core does not tell us the truth or both cores are distorted by the ice flow,” Kipfstuhl said.

Pieces of a Puzzle

Now a team of Europeans working on the ice cap just a few hundred miles north of Summit is drilling a third major core--the North Greenland Ice-core Project--in the hope they can resolve this troubling question about the instability of the warm climate during the Emean period.

And in Antarctica this November, a National Science Foundation-funded consortium of universities led by Taylor will start a three-year drilling effort at Siple Dome, where the ice is half a mile thick and encompasses the past 100,000 years, to see if they can confirm the troubling picture of climate change recorded at the other end of the world.

French, American and Russian teams have drilled long ice cores in Antarctica, but only in regions where the snowfall built up too slowly to record the kinds of abrupt climate changes observed in Greenland.

“Is the [climate] instability real?” asked Sigfus Johnsen, a glaciologist at the University of Iceland and the University of Copenhagen who is the chief scientist for the European project. “Is it something that we can expect to happen again?”

As he spoke, Johnsen slouched in an insulated freezer suit in front of a computer console in a snow cavern, dug to protect his crew and their equipment from the glacial wind. He guided a towering drill boring for the new ice core. In a nearby ice cave--where it was 14 below--cylindrical cores were racked on wooden shelves like bottles of rare wine.

“Here is snow that fell when Julius Caesar died,” said Kipfstuhl, pointing to one 9-foot-long section of core. “Here is when Vesuvius erupted” and buried Pompeii, Italy.

This summer, drillers reached 2,000 feet, where the snow fell more than 4,000 years ago. But it may be two years before the drilling is complete and researchers have the chance to determine the truth of the Emean climate and what it may portend.

“We live in an interglacial period and we think it is stable,” said Johnsen. “But it is difficult to see the real trends.

“These cores have shown us something unexpected, something that may require [environmental] policymakers to think again.”