David Frank on Global Carbon Cycle Sensitivity to Climate Changes

New Hot Paper Commentary, May 2011

David Frank

Article: Article Title: Ensemble reconstruction constraints on the global carbon cycle sensitivity to climate

Authors: Frank, DC;Esper, J;Raible, CC;Buntgen, U;Trouet, V;Stocker, B;Joos, F
Journal: NATURE
Volume: 463, Issue: 7280, Page: 527-U143, Year: JAN 28 2010
* Swiss Fed Res Inst WSL, Zurcherstr 111, CH-8903 Birmensdorf, Switzerland.
* Swiss Fed Res Inst WSL, CH-8903 Birmensdorf, Switzerland.
* Univ Bern, Oeschger Ctr Climate Change Res, CH-3012 Bern, Switzerland.
* Johannes Gutenberg Univ Mainz, Dept Geog, D-55099 Mainz, Germany.
* Univ Bern, Inst Phys, CH-3012 Bern, Switzerland.

David Frank talks with ScienceWatch.com and answers a few questions about this month's New Hot Paper in the field of Geosciences.

SW: Why do you think your paper is highly cited?

In our paper we addressed how the ocean and terrestrial biosphere releases and uptakes CO2 in response to changes in temperature. These processes will likely amplify anthropogenic emissions and global warming, but it is debated by how much. We were able to provide an answer to this question, and thus also help provide information needed to understand how much the planet will warm in the coming decades to centuries.

SW: Does it describe a new discovery, methodology, or synthesis of knowledge?

Our paper quantified the strength of the carbon cycle-climate feedback during the past Millennium. I see our manuscript as both a synthesis of knowledge and methodological innovation. To estimate the carbon-cycle climate feedback, we used all available climate reconstructions based upon tree-ring and other climate proxies and combined these with ice-core based estimates for past CO2 fluctuations. So in this sense, this is a compilation of knowledge and data developed by dozens of researchers over the past decades. We then applied an ensemble approach to climate reconstructions to derive probabilistic estimates for this feedback strength—more of a methodological innovation.

SW: Would you summarize the significance of your paper in layman's terms?

"In our study, we addressed how much the terrestrial and oceanic systems release CO2 in response to warming, and thereby amplify the effects of anthropogenic emissions and global warming"

The natural processes controlling the exchange and storage of carbon in the ocean and as well as on land are thought to be temperature-sensitive in such a way that they will accelerate global warming. However, the strength of this positive feedback is poorly known and leads to significant uncertainty in global warming projections.

Using temperature reconstructions and the concentration of CO2 gases trapped in ice cores, we found that for every °C temperature increase, CO2 in the atmosphere increased by ~8 parts per million. This is 80% smaller than some previous high-end estimates, and correspondingly suggests a reduced risk of catastrophic feedbacks.

In the future new processes and more extreme temperatures may come into play, so we also tested climate models abilities to reproduce past changes in the carbon cycle. We could identify some models that passed this first test with "better grades," suggesting these models might also do better for future predictions.

SW: 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?

I became involved in this research because of the important role tree-ring data serve in reconstructing regional to global temperatures. But as is true with all data, there is a certain amount of noise in these large-scale temperature reconstructions. I was working on ways to ensure that our estimates of past temperature change also considered uncertainties, and by doing so we were able to come up with a more probabilistic understanding of how temperature varied in the past. This is one of the puzzle pieces needed to understand many global change questions, including the sensitivity of the carbon cycle.

SW: Where do you see your research leading in the future?

My past research has focused on using the annual growth rings of trees as a tool to understand many global change related questions. In the future, I will answer questions about the impacts of climate and environmental (e.g., CO2) variation on tree growth and the terrestrial carbon cycle. With this understanding, I hope to develop a more accurate picture of how climate has varied in the past centuries to millennia, and how trees respond to environmental change and may grow in the future.

SW: Do you foresee any social or political implications for your research?

In our study, we addressed how much the terrestrial and oceanic systems release CO2 in response to warming, and thereby amplify the effects of anthropogenic emissions and global warming. Most, if not all, nations are now making policies about regulating greenhouse gas emissions to limit the atmospheric CO2concentration and thus also future warming. Our results can contribute to making more informed decisions.End

David Frank, Dendroclimatologist
Swiss Federal Research Institute WSL
Birmensdorf, Switzerland
Oeschger Centre for Climate Change Research
University of Bern
Bern, Switzerland



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