Letter | Published:

High levels of atmospheric carbon dioxide necessary for the termination of global glaciation

Nature volume 429, pages 646649 (10 June 2004) | Download Citation



The possibility that the Earth suffered episodes of global glaciation as recently as the Neoproterozoic period, between about 900 and 543 million years ago, has been widely discussed1,2,3. Termination of such ‘hard snowball Earth’ climate states has been proposed to proceed from accumulation of carbon dioxide in the atmosphere4. Many salient aspects of the snowball scenario depend critically on the threshold of atmospheric carbon dioxide concentrations needed to trigger deglaciation2,5. Here I present simulations with a general circulation model, using elevated carbon dioxide levels to estimate this deglaciation threshold. The model simulates several phenomena that are expected to be significant in a ‘snowball Earth’ scenario, but which have not been considered in previous studies with less sophisticated models, such as a reduction of vertical temperature gradients in winter, a reduction in summer tropopause height, the effect of snow cover and a reduction in cloud greenhouse effects. In my simulations, the system remains far short of deglaciation even at atmospheric carbon dioxide concentrations of 550 times the present levels (0.2 bar of CO2). I find that at much higher carbon dioxide levels, deglaciation is unlikely unless unknown feedback cycles that are not captured in the model come into effect.

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We thank P. Hoffman and S. Warren for discussions on a range of matters relating to the Neoproterzoic and to surface albedo in general; J.C.G. Walker for sharing additional thoughts concerning the Mars analogy; and LMD/Paris for providing a congenial environment in which to carry out this work. This work was funded by the National Science Foundation.

Author information


  1. Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA

    • Raymond T. Pierrehumbert


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Competing interests

The author declares that he has no competing financial interests.

Corresponding author

Correspondence to Raymond T. Pierrehumbert.

Supplementary information

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  1. 1.

    Supplementary Figure 1

    Comparison of OLR computed with the CCM3 radiation code used in the GCM experiments, and the more accurate Kasting-Ackermancode.

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