Robert F. Anderson Talks About rising CO2 Content of the Atmosphere
Fast Breaking Commentary, August 2010
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Article Title: Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2
Authors: Anderson, RF;Ali, S;Bradtmiller,
LI;Nielsen, SHH;Fleisher, MQ;Anderson, BE;Burckle, LH |
Robert F. Anderson talks with ScienceWatch.com and answers a few questions about this month's Fast Breaking Paper paper in the field of Geosciences.
Why do you think your paper is highly
cited?
Many people want to know why the concentration of carbon dioxide (CO2) in the atmosphere has been tightly coupled to Earth’s climate for at least the past 800,000 years. Although scientists established in the early 1980s that some combination of physical, chemical, and biological processes in the ocean must regulate the varying concentrations of CO2 in the atmosphere, the exact cause has remained a mystery.
A number of viable hypotheses have been proposed, but further research has shown that the hypotheses could not explain the observations. Our work provided support for one of the leading hypotheses. This positive result has been picked up by a number of other groups that are investigating other aspects of the link between CO2 and climate.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
"CO2 was an essential feedback mechanism, not the initial cause of climate change in the past, and that is why the rise in CO2 lagged the initial increase in temperature. I believe that this work contributes substantially toward a more complete knowledge of the role of CO2 in climate change..."
It involves a bit of each. We developed a new method to attack an old problem. We also combined our results from work in the ocean around Antarctica with results from other groups working in other regions to reach our conclusions.
Would you summarize the significance of your paper
in layman's terms?
We discovered evidence that the rate of mixing that stirs up deep waters in the ocean around Antarctica increased concurrently with rising CO2 content of the atmosphere. The deep ocean is a huge volume of water that is physically isolated from the atmosphere.
Because of this isolation, respiration by organisms living in the deep sea produces CO2 that accumulates for centuries before the gases are finally released to the atmosphere. All other things held constant, the faster that physical processes stir up deep water so it can release CO2 to the atmosphere, the greater will be the CO2 content of the atmosphere.
Our results, showing that increased rates of mixing coincided with rising atmospheric CO2 levels, indicate that this is a key process controlling natural variability in atmospheric CO2.
How did you become involved in this research, and
how would you describe the particular challenges, setbacks, and
successes that you've encountered along the way?
This work represented the convergence of two previous projects. In one, we examined ocean sediments around Antarctica for evidence to test the famous "iron hypothesis" developed by the late John Martin.
This hypothesis proposed that the greater abundance of dust in the atmosphere during the ice ages added iron to the ocean. Algae in the ocean around Antarctica have plenty of other nutrients (such as nitrogen), but their growth, and thus their ability to consume CO2, is limited by the scarcity of iron. Dust supplies iron, and so it was thought that the greater abundance of dust during the ice ages may have stimulated the growth of algae and thereby lowered the CO2 content of the atmosphere.
Our work disproved the iron hypothesis, but the work stimulated our thinking about the mixing processes described in the more recent study. The second project investigated the factors that limit the growth of algae in the ocean around Antarctica today. Combining results from research on the modern ocean with our findings on changes in the past led to the recent paper that is the subject of this ScienceWatch piece.
Where do you see your research leading in the
future?
Research in two areas will build upon our findings. First, our work provides one key piece of the puzzle representing the ensemble of processes that cause CO2 to be tightly coupled to climate. But it does not cover the whole story. With this piece in place, it will be much easier to complete the rest of the puzzle.
Second, in order to explain the ocean’s control of atmospheric CO2 levels we invoke a sequence of processes that begin in the high latitudes of the northern hemisphere and propagate all the way to Antarctica. Some of these processes for which we find evidence in the geological record are not reproduced in climate models. Either we are misinterpreting the geological record or there is something important about climate that is not being coded correctly in models. Resolving this discrepancy will contribute to our understanding of climate change, both in the past and in the future.
Do you foresee any social or political implications for your research?
Yes, especially when combined with a subsequent study that was just published (June 25, 2010, SCIENCE). Together, the two papers describe the full sequence of processes that link climate and CO2 at the end of the last ice age. Many so-called climate skeptics assert that the 800-year lag between the initial warming in Antarctica and the rise in CO2 at the end of the last ice age demonstrates that CO2 has no role in forcing climate change. We disagree with that view.
Together, the two papers explain why CO2 lagged the initial temperature
rise in Antarctica, and still played a critical role in warming the earth.
CO2 was an essential feedback mechanism, not the initial cause of climate
change in the past, and that is why the rise in CO2 lagged the initial
increase in temperature. I believe that this work contributes substantially
toward a more complete knowledge of the role of CO2 in climate
change.
Robert F. Anderson, Ph.D.
Ewing-Lamont Research Professor
Lamont-Doherty Earth Observatory of Columbia
University
Palisades, NY, USA
and
Adjunct Professor
Department of Earth and Environmental Sciences
Columbia University
New York, NY, USA
KEYWORDS: WIND-DRIVEN UPWELLING, SOUTHERN OCEAN, ATMOSPHERIC CO2, LAST GLACIAL PERIOD, PAST 50,000 YEARS, CLIMATE CHANGE, LATE PLEISTOCENE, PACIFIC SECTOR, CARBON CYCLE, PARTICLE COMPOSITION, TROPICAL ATLANTIC, NORTH ATLANTIC, ICE CORES.