Carbon dioxide level highest in 650,000 years
November 24, 2005
Carbon dioxide levels are now 27 percent higher than at any point in the last 650,000 years, according to research into Antarctic ice cores published on Thursday in Science.
Analysis of carbon dioxide in the ancient Antarctic ice showed that at no point in the past 650,000 years did levels approach today’s carbon dioxide concentrations of around 380 parts per million (ppm). The Intergovernmental Panel on Climate Change (IPCC) projects that atmospheric carbon dioxide levels could reach 450-550 ppm by 2050, possibly resulting in higher temperatures and rising sea levels (see “Ocean levels rising twice as fast“). There is fear that climate change could create a class of environmental refugees displaced from their homes by rising oceans, increasingly catastrophic weather, and expanding deserts.
Carbon dioxide is the principal “greenhouse” gas thought to be driving global warming. Humans boost carbon dioxide levels primarily by the combustion of fossils fuels and deforestation, and accordingly, atmospheric concentrations have risen sharply since the industrial revolution. Today the United States, the world’s largest economy and consumer of energy, produces about 24% of global carbon dioxide emissions.
Below are two news releases from organizations involved in the Antarctic ice core research, American Association for the Advancement of Science and Oregon State University.
Today’s atmospheric carbon dioxide levels are highest in 650,000 years, Science studies say
With the first in-depth analysis of the air bubbles trapped in the “EPICA Dome C” ice core from East Antarctica, European researchers have extended the greenhouse gas record back to 650,000 years before the present.
This 210,000-year extension of atmospheric carbon dioxide and methane records — encompassing two full glacial cycles — should help scientists better understand climate change and the nature of the current warm period on Earth. The record may also aid researchers in reducing uncertainty in predictions of future climate change and help to clarify when humans began significantly changing the balance of greenhouse gasses in Earth’s atmosphere.
EPICA is the European Project for Ice Coring in Antarctica. The new ice core, initially described in 2004, is from a site in East Antarctica known as EPICA Dome C. This work represents a long-term European research collaboration and appears in two studies and an accompanying “Perspective” article in the 25 November 2005 issue of the journal Science, published by AAAS the nonprofit science society.
One study chronicles the stable relationship between climate and the carbon cycle during the Pleistocene (390,000 to 650,000 years before the present). The second one documents atmospheric methane and nitrous oxide levels over the same period. .
The analysis highlights the fact that today’s rising atmospheric carbon dioxide concentration, at 380 parts per million by volume, is already 27 percent higher than its highest recorded level during the last 650,000 years, said Science author Thomas Stocker of the Physics Institute of the University of Bern, in Bern, Switzerland, who serves as the corresponding author for both papers.
“We have added another piece of information showing that the timescales on which humans have changed the composition of the atmosphere are extremely short compared to the natural time cycles of the climate system,” Stocker explained.
The new work confirms the stable relationship between Antarctic climate and the greenhouse gasses carbon dioxide and methane during the last four glacial cycles. The new ice core analysis also extends this relationship back another two glacial cycles, to a time when the warm “interglacial” periods were milder and longer than more recent warm periods, according to the European researchers.
The fact that carbon dioxide and methane levels were lower during the relatively mild warm periods of the two additional cycles, compared to the warmer warm periods of the last 400,000 years, is especially interesting for the study of climate sensitivity, which is a measure of how the climate system reacts when atmospheric carbon dioxide concentrations double, explained Science author Dominique Raynaud from LGGE in Grenoble, France.
The new atmospheric and climate records from the EPICA Dome C ice core also indicate that the response of the natural carbon cycle to climate warming remains the same over time in terms of the mechanism involved and the degree to which greenhouse gasses further amplify climate change, explained Science author Jean Jouzel from LSCE and Institut Pierre Simon Laplace in France.
The EPICA Dome C ice core contains hundreds of thousands of years-worth of atmospheric air samples within tiny bubbles trapped in the ice. The air bubbles form when snowflakes fall, and they contain a record of global greenhouse gas concentrations.
The new ice core record described in the two Science papers provides some overlap with a similar record from the Vostok ice core now, the second longest ice core record — and extends the Vostok record by 210,000 years.
The nitrous oxide record in EPICA Dome C is more fragmented and less clear than the carbon dioxide and methane records due to artifacts in the ice that appear related to the dust levels.
The new ice core analysis provides insights on our present interglacial warm period through a glimpse into Antarctic climate and greenhouse gas concentrations during the most recent warm period that is relatively similar to our current warm period. Known as Marine Isotope Stage 11 or MIS 11, this analog warm period occurred between 420,000 and 400,000 years and is not completely covered by the Vostok record.
The similarities between our current warm period and MIS 11 are primarily due to a similar configuration of the orbits of the Earth around the Sun: the relative positions of the Earth and Sun are thought to be the key driver of ice age cycles.
“MIS 11 shows us that the climate system can indeed reside in a warm period for 20,000 or 30,000 years, something that we can’t say based on the last three warm phases which are no longer than about 10,000 years each,” said Stocker.
We are currently about 10,000 years into our current warm period.
The new papers also document MIS 13 and 15 — two warm periods more distant than MIS 11 that may have been about as long. The idea that MIS 13 and 15 were long warm periods contrasts the argument scientists have made in the past suggesting that our current warm period is exceptionally long.
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The authors note, however, that the records for MIS 13 and 15 are not as clear as they are for MIS 11. One complicating factor is that the ice core records do not exactly match records from marine sediments that are used to help date the ice core data.
New insights important for understanding the impact early human activities such as land clearing and rice culture had on atmospheric greenhouse gas concentrations, the topic of several recent studies, are also now available, thanks to the methane and carbon dioxide records from the EPICA Dome C ice core. The new record shows that natural variability can result in significant oscillations in greenhouse gasses during some interglacial periods and raises the possibility that early human activities may not be responsible for the greenhouse gas variability seen as early as 10,000 years ago, writes Ed Brook from Oregon State University in Corvallis, Oregon in a related “Perspective” article.
The greenhouse gas record from EPICA Dome C during past ice ages also provides indirect evidence for abrupt climate change in the past, the authors found. This suggests that abrupt climatic events on time scales relevant to societies may be common features of the last climatic cycles.
The stable relationship between carbon dioxide, methane and Antarctic climate over the last 650,000 years highlights one of the major unsolved mysteries of climate change — the origins of climate-greenhouse gas relationships. Organic decomposition in subtropical wetlands remains a strong candidate for explaining the climate-methane relationship. On the other hand, oceans seem to play a critical role in the climate-carbon dioxide relationship; and the new work strengthens the idea that high latitude Southern Ocean processes are important for controlling glacial-interglacial variations in carbon dioxide, according to the “Perspective” author who says that retrieval and analysis of even older ice cores may provide more definitive answers.
“Stable Carbon Cycle-Climate Relationship During the Late Pleistocene,” by U. Siegenthaler, T.F. Stocker, E. Monnin, D. Lüthi, J. Schwander and B. Stauffer at University of Bern, in Bern, Switzerland; D. Raynaud and J.-M. Barnola at Laboratoire de Glaciologie et de Géophysique de l’Environnement (CNRS) St Martin d’Hères Cedex, France; H. Fischer at Alfred-Wegener-Institute for Polar and Marine Research (AWI) in Bremerhaven, Germany; V. Masson-Delmotte and J. Jouzel at LSCE and Institut Pierre Simon Laplace in France.
“Atmospheric Methane and Nitrous Oxide of the Late Pleistocene from Antarctic Ice Cores,” by R. Spahni, T. Stocker, G. Hausammann, K. Kawamura, J. Flückiger and Jakob Schwander at University of Bern, in Bern, Switzerland; J. Chappellaz, L. Loulergue and D. Raynaud at Laboratoire de Glaciologie et de Géophysique de l’Environnement (CNRS) in St Martin d’Hères Cedex, France; V. Masson-Delmotte, J. Jouzel at LSCE and Institut Pierre Simon Laplace in France. K. Kawamura is now at Scripps Institution of Oceanography, University of California, San Diego, La Jolla, United States. J. Flückiger is now at Institute of Arctic and Alpine Research, University of Colorado at Boulder in Colorado, United States.
The accompanying “Perspective” article “Tiny Bubbles Tell All,” is by E. Brook from Oregon State University in Corvallis, Oregon, United States.
The work described in the Siegenthaler et al. and Spahni et al. Science papers is a contribution to the “European Project for Ice Coring in Antarctica” (EPICA), a joint ESF (European Science Foundation)/EC scientific programme, funded by the European Commission and by national contributions from Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Sweden, Switzerland and the United Kingdom. The researchers acknowledge long-term financial support by the Swiss NSF, the University of Bern and the Swiss Federal Agency of Energy, and EC Project EPICA-MIS. Support was also provided by the French programme PNEDC (INSU-CNRS).
The American Association for the Advancement of Science (AAAS) is the world’s largest general scientific society, and publisher of the journal, Science (www.sciencemag.org). AAAS was founded in 1848, and serves some 262 affiliated societies and academies of science, serving 10 million individuals. Science has the largest paid circulation of any peer-reviewed general science journal in the world, with an estimated total readership of one million. The non-profit AAAS (www.aaas.org) is open to all and fulfills its mission to “advance science and serve society” through initiatives in science policy; international programs; science education; and more. For the latest research news, log onto EurekAlert!, www.eurekalert.org, the premier science-news Web site, a service of AAAS.
This is a modified press release from the American Association for the Advancement of Science
CORVALLIS, Ore. Two new studies of gases trapped in Antarctic ice cores have extended the record of Earth’s past climate almost 50 percent further, adding another 210,000 years of definitive data about the makeup of the Earth’s atmosphere and providing more evidence of current atmospheric change.
The research is being published in the journal Science by participants in the European Project for Ice Coring in Antarctica. It’s “an amazing accomplishment we would not have thought possible” as recently as 10 years ago, said Ed Brook, a professor of geosciences at Oregon State University, who analyzed the studies in the same issue of this professional journal.
“Not long ago we thought that previous ice studies which go back about 500,000 years might be the best we could obtain,” said Brook, who is also the co-chair of the International Partnerships in Ice Coring Sciences, a group that’s helping to plan future ice core research efforts around the world.
“Now we have a glimpse into the past of up to 650,000 years, and we believe it may be possible to go as much as one million years or more,” Brook said. “This will give us a fuller picture of Earth’s past climates, the way they changed and fluctuated, and the forces that caused the changes. We’ll be studying this new data for years.”
As the data become more solid about the atmospheric conditions of the past, it’s becoming increasingly clear that the current conditions of the past 200 years are a distinct anomaly, Brook said.
“The levels of primary greenhouse gases such as methane, carbon dioxide and nitrous oxide are up dramatically since the Industrial Revolution, at a speed and magnitude that the Earth has not seen in hundreds of thousands of years,” Brook said. “There is now no question this is due to human influence.”
The ice cores being taken from Greenland, Antarctica and other sites provide an invaluable record of Earth’s past climates, researchers say. By testing the gases and trace elements found trapped in these cores, scientists gain a better understanding of how climate and atmospheric gases interact and evolve.
“We predict, for instance, that rising levels of greenhouse gases will warm our climate,” Brook said. “There’s evidence that this is happening right now, and it would be interesting to find out if the same thing has happened at times in the distant past. And there are also concerns we’re exploring about rapid shifts in climate.”
Analysis of the older cores just removed from Antarctica, Brook said, are consistent with some of the quick changes in methane and carbon dioxide levels that are related to abrupt climate change. However, it also appears that the natural climate cycles in the distant past the development and retreat of Ice Ages, for instance were smaller in magnitude and had less fluctuation in atmospheric gases than what the Earth is now experiencing.
There are critical questions that work of this type may help answer, researchers say. One of the most obvious is the relationship between increasing levels of greenhouse gases and global warming. But there are also concerns that the Earth’s climate may have changed very abruptly at times in the past, in complex interactions between the atmosphere, ocean currents and ice sheets.
Past studies of gases trapped in Greenland and Antarctic ice cores have suggested that Earth’s temperature can sometimes change amazingly fast, warming as much as 15 degrees in some regions within a couple of decades. At the same time, there are concerns about the change of major ocean currents, such as those in the North Atlantic Ocean, that are responsible for the comparatively mild climate of much of Europe. If that “thermohaline circulation pattern” were to abruptly shut down, as has happened at times in the past, it could plunge much of the European continent into a climate more closely resembling that of central Canada.
According to Brook, continuing research will help to address many of these questions. The international committee he co-chairs, which involves representatives from 17 nations, is considering such work as a very deep ice coring project in Antarctica that might provide a record of atmospheric gases 1.2 million years ago, or even further back in time. Other studies are also anticipated in Greenland and the Arctic.
Some of these projects will require drilling in challenging locations on very old ice, Brook said, at considerable cost in initiatives that require international cooperation.
“Ice cores are the cornerstones of global change research,” Brook said. “They have played a central role in showing how closely climate and greenhouse gas concentrations were linked in the past, and they are demonstrating also that very abrupt climate switches can occur.”
This is a modified press release from the Oregon State University