Deep ice tells long climate story
By Jonathan Amos
Science reporter, BBC News, Norwich
Carbon dioxide levels are substantially higher now than at any time in the last 800,000 years, the latest study of ice drilled out of Antarctica confirms.
The in-depth analysis of air bubbles trapped in a 3.2km-long core of frozen snow shows current greenhouse gas concentrations are unprecedented.
The East Antarctic core is the longest, deepest ice column yet extracted.
Project scientists say its contents indicate humans could be bringing about dangerous climate changes.
"My point would be that there's nothing in the ice core that gives us any cause for comfort," said Dr Eric Wolff from the British Antarctic Survey (BAS).
"There's nothing that suggests that the Earth will take care of the increase in carbon dioxide. The ice core suggests that the increase in carbon dioxide will definitely give us a climate change that will be dangerous," he told BBC News.
The Antarctic researcher was speaking here at the British Association's (BA) Science Festival.
Slice of history
The ice core comes from a region of the White Continent known as Dome Concordia (Dome C). It has been drilled out by the European Project for Ice Coring in Antarctica (Epica), a 10-country consortium.
The column's value to science is the tiny pockets of ancient air that were locked into its millennia of accumulating snowflakes.
Each slice of this now compacted snow records a moment in Earth history, giving researchers a direct measure of past environmental conditions.
Not only can scientists see past concentrations of carbon dioxide and methane - the two principal human-produced gases now blamed for global warming - in the slices, they can also gauge past temperatures from the samples.
This is done by analysing the presence of different types, or isotopes, of hydrogen atom that are found preferentially in precipitating water (snow) when temperatures are relatively warm.
'Scary' rate
Earlier results from the Epica core were published in 2004 and 2005, detailing the events back to 440,000 years and 650,000 years respectively. Scientists have now gone the full way through the column, back another 150,000 years.
The picture is the same: carbon dioxide and temperature rise and fall in step.
Microscope picture of gas bubbles in ice. Image: W. Berner/University of Bern
Like tiny time capsules, bubbles trap ancient samples of atmosphere
"Ice cores reveal the Earth's natural climate rhythm over the last 800,000 years. When carbon dioxide changed there was always an accompanying climate change. Over the last 200 years human activity has increased carbon dioxide to well outside the natural range," explained Dr Wolff.
The "scary thing", he added, was the rate of change now occurring in CO2 concentrations. In the core, the fastest increase seen was of the order of 30 parts per million (ppm) by volume over a period of roughly 1,000 years.
"The last 30 ppm of increase has occurred in just 17 years. We really are in the situation where we don't have an analogue in our records," he said.
Natural buffer
The plan now is to try to extend the ice-core record even further back in time. Scientists think another location, near to a place known as Dome A (Dome Argus), could allow them to sample atmospheric gases up to a million and a half years ago.
Some of the increases in carbon dioxide will be alleviated by natural "sinks" on the land and in the oceans, such as the countless planktonic organisms that effectively pull carbon out of the atmosphere as they build skeletons and shell coverings.
But Dr Corinne Le Quéré, of the University of East Anglia and BAS, warned the festival that these sinks may become less efficient over time.
We could not rely on them to keep on buffering our emissions, she said.
"For example, we don't know what the effect will be of ocean acidification on marine ecosystems. There is potential for deterioration," she explained.
More CO2 absorbed by the oceans will raise their acidity, and a number of recent studies have concluded that this will eventually disrupt the ability of marine micro-organisms to use the calcium carbonate in the water to produce their hard parts.
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Ancient Air Bubbles yield Greenhouse-gas Concerns
There is more carbon dioxide in the atmosphere today than at any point during the past 650,000 years, says a major new study that let scientists peer back in time at "greenhouse gases" that can help fuel global warming.
By analyzing tiny air bubbles preserved in Antarctic ice for millennia, a team of European researchers highlights how people are dramatically influencing the buildup of these gases.
The remarkable research promises to spur "dramatically improved understanding" of climate change, said geosciences specialist Edward Brook of Oregon State University.
The study, by the European Project for Ice Coring in Antarctica, is published today in the journal Science.
Today, scientists directly measure levels of carbon dioxide and other greenhouse gases, which accumulate in the atmosphere as a result of fuel-burning and other processes. Those gases help trap solar heat, like the greenhouses for which they are named, resulting in a gradual warming of the planet.
Those measurements are disturbing: Levels of carbon dioxide have climbed from 280 parts per million two centuries ago to 380 ppm today. Earth's average temperature, meanwhile, increased about 1 degree Fahrenheit in recent decades, a relatively rapid rise. Many climate specialists warn that continued warming could have severe impacts, such as rising sea levels and changing rainfall patterns.
Skeptics sometimes dismiss the rise in greenhouse gases as part of a naturally fluctuating cycle.
The new study provides ever-more definitive evidence countering that view, however.
Deep Antarctic ice encases tiny air bubbles formed when snowflakes fell over hundreds of thousands of years. Extracting the air allows a direct measurement of the atmosphere at past points in time, to determine the naturally fluctuating range.
A previous ice-core sample had traced greenhouse gases back about 440,000 years. This new sample, from East Antarctica, goes 210,000 years further back in time.
Today's still-rising level of carbon dioxide already is 27 percent higher than its peak during all those millennia, said lead researcher Thomas Stocker of the University of Bern, Switzerland.
"We are out of that natural range today," he said.
Moreover, that rise is occurring at a speed that "is over a factor of a hundred faster than anything we are seeing in the natural cycles," Stocker added. "It puts the present changes in context."
The team, which included scientists from France and Germany, found similar results for methane, another greenhouse gas.
Researchers also compared the gas levels to the Antarctic temperature over that time, covering eight cycles of alternating glacial or ice ages and warm periods. They found a stable pattern: Lower levels of gases during cold periods and higher levels during warm periods.
The bottom line: "There's no natural condition that we know about in a really long time where the greenhouse-gas levels were anywhere near what they are now. And these studies tell us that there's a strong relationship between temperature and greenhouse gases," explained Oregon State's Brook.
"Which logically leads you to the conclusion that maybe we should worry about temperature change in the future."
A lengthening history of greenhouse-gas concentrations should help climate specialists build better models about what the future might bring, Stocker said.
It also may help answer additional questions such as how long ago humans started influencing greenhouse-gas accumulations, and what impact other factors such as ocean currents play in the complexities of climate change.
The bottom line: "There's no natural condition that we know about in a really long time where the greenhouse-gas levels were anywhere near what they are now. And these studies tell us that there's a strong relationship between temperature and greenhouse gases," explained Oregon State's Brook. Core Drilling
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