Ice core data - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 156

Figure 4.21. Variation of CO 2 concentration since the LGM. The KK data and spline fit were
based on 10 ice core results fromKrumhardt and Kaplan (2010). The JS spline fit is to 4 ice core
results (Joos and Spahni, 2008).

However, there is some evidence that CO 2 concentration rise (or fall) lags
temperature rise (or fall) that occurs during periods of increased glaciation or
warming at Antarctica. The time lag was estimated to be 500 years by Roper
(2006), 800 200 years by Caillon et al. (2003), 1,300-5,000 years by Mudelsee
(2001), 800 years by Monnin et al. (2001), and 400-1,000 years by Fischer et al.
(1999). That would seem to imply that increased CO 2 is mainly an effect, not a
cause of temperature change, although it would provide positive feedback and
thus be both a primary effect and a secondary cause.
As the Last Glacial Maximum (LGM) faded and the Earth warmed, the CO 2
concentration rose in response. Analysis of several ice cores led to the time depen-
dence of CO 2 concentration over the past 25,000 years as shown in Figure 4.21 .
Skinner (2006) provided a recent review of the subject of glacial-interglacial
CO 2 cycles. He emphasized that, even though it is clear that changes in
atmospheric CO 2 were tightly coupled to global climate change throughout
the past 800,000 years, the mechanisms responsible for these changes in CO 2
concentration ''remain a mystery''. Archer et al. (2000) came to similar

conclusions:

''In spite of the clear importance of pCO 2 as an amplifier or even a
primary driver of the glacial cycles, and the additional motivation provided by
the threat of future climate change, we remain ignorant of the mechanisms
responsible for the glacial/interglacial CO 2 cycles . Fifteen years after the

discovery of major glacial/interglacial cycles in the CO 2 concentration of the
atmosphere, it seems that all of the simple mechanisms for lowering pCO 2 have
been eliminated.''

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