CO2 feedback recalculated

Editor's Summary

Nature, 28 January 2010

http://www.nature.com/nature/journal/v463/n7280/edsumm/e100128-07.html

Climate warming tends to cause a net release of CO₂, which in turn causes an amplification of warming. Estimates of the magnitude of this effect vary widely, leading to a wide range in global warming projections. Recent work suggested that the magnitude of this positive feedback might be about 40 parts per million by volume of CO₂ per °C of warming. David Frank and colleagues use three Antarctic ice cores and a suite of climate reconstructions to show that the feedback is likely to be much smaller, with a median of only about 8 p.p.m.v. CO₂ per °C.

AUTHORS:Making the paper: David Frank

Wealth of data cuts uncertainty in climate-warming predictions.

doi:10.1038/7280400a

Full Text | PDF (618K)

NEWS AND VIEWS:Carbon cycle: Degrees of climate feedback

A probabilistic analysis of climate variation during the period AD 1050–1800 refines available estimates of the influence of temperature change on the concentration of carbon dioxide in the atmosphere.

Hugues Goosse

doi:10.1038/463438a

Full Text | PDF (971K)

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

David C. Frank, Jan Esper, Christoph C. Raible, Ulf Büntgen, Valerie Trouet, Benjamin Stocker & Fortunat Joos

doi:10.1038/nature08769

First paragraph | Full Text | PDF (4,293K) | Supplementary information

Letter

Nature 463, 527-530 (28 January 2010) | doi:10.1038/nature08769; Received 24 July 2009; Accepted 12 December 2009

Ensemble reconstruction constraints on the global carbon cycle sensitivity to climate

David C. Frank^1,2, Jan Esper³, Christoph C. Raible^2,4, Ulf Büntgen¹, Valerie Trouet¹, Benjamin Stocker^2,4 & Fortunat Joos^2,4

1. Swiss Federal Research Institute WSL, Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland
2. Oeschger Centre for Climate Change Research, University of Bern, Zähringerstrasse 25, CH-3012 Bern, Switzerland
3. Department of Geography, Johannes Gutenberg University, Becherweg 21, 55099 Mainz, Germany
4. Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland

Correspondence to: David C. Frank^1,2 Correspondence and requests for materials should be addressed to D.C.F. (Email: david.frank@wsl.ch).

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Abstract

The processes controlling the carbon flux and carbon storage of the atmosphere, ocean and terrestrial biosphere are temperature sensitive^{1, 2, 3, 4} and are likely to provide a positive feedback leading to amplified anthropogenic warming³. Owing to this feedback, at timescales ranging from interannual to the 20–100-kyr cycles of Earth's orbital variations^{1, 5, 6, 7}, warming of the climate system causes a net release of CO₂ into the atmosphere; this in turn amplifies warming. But the magnitude of the climate sensitivity of the global carbon cycle (termed γ), and thus of its positive feedback strength, is under debate, giving rise to large uncertainties in global warming projections^8, 9. Here we quantify the median γ as 7.7 p.p.m.v. CO₂ per °C warming, with a likely range of 1.7–21.4 p.p.m.v. CO₂per °C. Sensitivity experiments exclude significant influence of pre-industrial land-use change on these estimates. Our results, based on the coupling of a probabilistic approach with an ensemble of proxy-based temperature reconstructions and pre-industrial CO₂ data from three ice cores, provide robust constraints for γ on the policy-relevant multi-decadal to centennial timescales. By using an ensemble of >200,000 members, quantification of γ is not only improved, but also likelihoods can be assigned, thereby providing a benchmark for future model simulations. Although uncertainties do not at present allow exclusion of γ calculated from any of ten coupled carbon–climate models, we find that γ is about twice as likely to fall in the lowermost than in the uppermost quartile of their range. Our results are incompatibly lower (P < 0.05) than recent pre-industrial empirical estimates of ~40 p.p.m.v. CO₂ per °C (refs 6, 7), and correspondingly suggest ~80% less potential amplification of ongoing global warming.

1. Swiss Federal Research Institute WSL, Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland
2. Oeschger Centre for Climate Change Research, University of Bern, Zähringerstrasse 25, CH-3012 Bern, Switzerland
3. Department of Geography, Johannes Gutenberg University, Becherweg 21, 55099 Mainz, Germany
4. Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland

Correspondence to: David C. Frank^1,2 Correspondence and requests for materials should be addressed to D.C.F. (Email: david.frank@wsl.ch).