This in interesting because there appears to be demonstrable loss of ice, especially shelves, in lower-CO2 conditions at present.
Could differences in solar output, etc., be behind the apparent differences in ice accumulation/loss? A 2009/9/14 Greg Rau <[email protected]>: > Nature advance online publication 13 September 2009 | > doi:10.1038/nature08447; Received 18 May 2009; Accepted 21 August 2009; > Published online 13 September 2009 > > Atmospheric carbon dioxide through the Eocene-Oligocene climate transition > Paul N. Pearson1, Gavin L. Foster2 & Bridget S. Wade3 > 1. School of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 > 3YE, UK > 2. Bristol Isotope Group, Department of Earth Sciences, University > of Bristol, Bristol BS8 1RJ, UK > 3. Department of Geology and Geophysics, Texas A&M University, College > Station, Texas 77843-3115, USA > Correspondence to: Paul N. Pearson1 Correspondence and requests for > materials should be addressed to P.N.P. (Email: [email protected]). > > Abstract > Geological and geochemical evidence1, 2, 3 indicates that the Antarctic ice > sheet formed during the Eocene-Oligocene transition4, 33.5-34.0 million > years ago. Modelling studies5, 6 suggest that such ice-sheet formation might > have been triggered when atmospheric carbon dioxide levels (pCO2 atm) fell > below a critical threshold of 750 p.p.m.v., but the timing and magnitude of > pCO2 atm relative to the evolution of the ice sheet has remained unclear. > Here we use the boron isotope pH proxy7, 8 on exceptionally well-preserved > carbonate microfossils from a recently discovered geological section in > Tanzania9, 10 to estimate pCO2 atm before, during and after the climate > transition. Our data suggest that a reduction in pCO2 atm occurred before > the main phase of ice growth, followed by a sharp recovery to pre-transition > values and then a more gradual decline. During maximum ice-sheet growth, > pCO2 atm was between 450 and 1,500 p.p.m.v., with a central estimate of > 760 p.p.m.v. The ice cap survived the period of pCO2 atm recovery, although > possibly with some reduction in its volume, implying (as models predict11) a > nonlinear response to climate forcing during melting. Overall, our results > confirm the central role of declining pCO2 atm in the development of the > Antarctic ice sheet (in broad agreement with carbon cycle modelling12) and > help to constrain mechanisms and feedbacks associated with the Earth's > biggest climate switch of the past 65 Myr. > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
