under a Creative Commons License. Climate of the Past Discussions Interactive comment on “Ice-driven CO2 feedback

• Main Author: P. Köhler
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2006
• Subjects: Ice Sheet
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.518.6137; http://www.cosis.net/copernicus/EGU/cpd/2/S17/cpd-2-S17_p.pdf?PHPSESSID=970f14118aefecc68cd6fd1015681fbe

This article is an interesting contribution towards the “chicken-egg ” discussion, what was first on glacial/interglacial timescales: the rise in atmospheric CO2 or in tem-perature respectively land ice sheets. The author divides the component of the CO2 variations into three different frequency bands known to be important from variation in orbital forcing. According to the author CO2 is driven by ice sheet growth in two of the frequency bands ((41 kyr)−1, (100 kyr)−1), while it is leading ice sheet growth in the third band ((23 kyr)−1). The author recognizes in his manuscript the limitations of traditional spectral analysis in resolving leads and lags in data which obviously is not just a sum of sine functions but a nonlinear response to an external forcing. It is worth noting that for the most dramatic change in ice volume and CO2, i.e. during S17 glacial/interglacial transitions, where phasing can be unabiguously determined, CO2 significantly leads ice volume. In addition to methodological limitations of a spectral analysis approach any statistical (lagged) correlation of ice volume and CO2 changes does not necessarily imply causality. Accordingly, any hypothesis of ice sheet forcing