WEST ANTARCTICA—At a camp here on Earth’s remotest continent, American researchers have constructed a towering drill that, like a biopsy needle, periodically plunges thousands of feet into the ice to extract an exotic marrow of frozen gases and isotopes.
Their work could settle a central question in the dispute over climate change, by documenting how greenhouse gases influenced temperatures in the past. Only then can researchers accurately analyze climate changes that may be under way today.
Until now, that information was hidden in Antarctica’s ancient ice.
Scientists agree that global temperatures are rising, and so are levels of carbon dioxide. But the immediate impact of human activity on natural climate cycles—from ice-sheet dynamics to wind and ocean currents—remains unclear. The Antarctica research could, for the first time, teach scientists how global warming developed when humankind had no hand in it.
“One of the questions that everybody is interested in with greenhouse gases is, did the increase in greenhouse gas concentrations occur before or after the increase in temperatures in the past climate changes?” says glaciologist Kendrick Taylor, chief scientist of the $30 million U.S. National Science Foundation project. “Ice cores are the only way we can answer that question.”
Ten times a day, scientists here recently winched up a 10-foot cylinder of compacted ice crystals containing the unsullied air and chemicals trapped by snowfall for the past 100,000 years.
Each cylinder preserves bubbles of ancient air and layers of elements swept here by global winds. The ice records the annual rise and fall of greenhouse gases and temperatures every year since before the last Ice Age, laminated by the cold in a parfait of time two miles thick.
In March, a shipment of this rare ice completed an 8,000-mile journey to the National Ice Core Laboratory in Denver, where it will be parceled out for analysis. Only Antarctica offers such a detailed calendar of climate change, the scientists say.
Since November, revelations of errors in reports by the United Nations’ Intergovernmental Panel on Climate Change have sapped public confidence in climate predictions. The scientists in Antarctica are excavating the ice as a reality check on computer climate models at the heart of today’s regulatory debates.
Much of the current controversy over climate change centers on efforts to reconstruct past temperatures using what is known as “proxy” data from tree rings, harvest records, sea beds and lake sediments. Unlike ice cores, which contain telltale gases and particles from ages ago, the proxy data offer only indirect or fragmentary evidence of climate trends.
“Unfortunately many of our proxies have significant errors and are prone to be a slave to assumptions,” says climatologist John Christy of the University of Alabama in Huntsville, who has often criticized the IPCC. His research, using temperature readings from NOAA and NASA satellites, has undermined arguments that the atmosphere is warming at an unusual rate.
The ice-core data from Antarctica is “terribly important,” Dr. Christy says. “We really need to know what the climate did before we can answer why it did what it did. If it happened before, it will happen again, and probably worse.”
The first samples already reveal intriguing evidence of climate complexity. In ice layers attributed to the Middle Ages, when Europe was unusually warm, the team found surprisingly high levels of carbon black particles, or soot. Levels were found to be twice as high as during the more heavily populated and industrialized 20th century, says geochemist Ross Edwards at the Desert Research Institute in Reno, Nev.
Overlooked in climate projections until recently, carbon black is a powerful warming agent. The soot, scientists speculate, came from giant wildfires that likely occurred in Australia and South America. So much soot could have raised temperatures.
Preliminary tests also showed that soot levels dropped during the cooler centuries after the Middle Ages, a period known as the Little Ice Age.
With more ice data, scientists hope to pin down the role of carbon dioxide in past global-warming episodes. Rising levels of greenhouse gases like CO2 in the atmosphere today are attributed to fossil-fuel emissions, land-use changes, cement production and agriculture. But no one is certain what made greenhouse gases fluctuate in the past.
During Ice Age cycles of cooling and warming, temperatures often rose before levels of carbon dioxide changed—sometimes 800 years or so before—according to previous evidence of ice from Antarctica.
“You don’t expect the cause to follow the effect,” says atmospheric scientist Richard S. Lindzen at the Massachusetts Institute of Technology, a frequent IPCC critic. “That’s become an important issue.”
Skeptics of carbon dioxide’s role in global warming have made much of this discrepancy. They don’t question the reliability of the data, but its interpretation, Dr. Lindzen says.
Climate scientists offer explanations for the lag, from periodic variations in solar radiation due to Earth’s orbit and changing ocean currents, to problems with the dating of the data itself. But they lack enough information to prove them.