Overview of the various models for ice ages in the recent past (3 MYBP to present) - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 236

years, the rate of 10 Be production was predominantly higher than today, although
there were four periods when the 10 Be rate was as low as the current rate. These
periods included 230-190, 135-110, 85-75, and 50-43 kybp . Comparison with
Figure 4.10 shows that 230-190 kybp was associated with a moderate interglacial
period, 135-110 kybp was associated with a major deglaciation, 85-75 kybp was
associated with a short-term spike in temperature, and the period 50-43 kybp was
associated with climatic instability. Thus, there are at least some indications that
the level of cosmic ray flux may affect climate over time spans of hundreds of
thousands of years. Kirkby et al. (2004) actually proposed ''a new model for the
glacial cycles in which the forcing mechanism is due to galactic cosmic rays,
probably through their effect on clouds.'' They based this on ''the accumulated
experimental evidence of the last few years as well as new results presented here
on a 220,000-year record of GCR flux obtained in deep-ocean sediments.'' They
concluded that the evidence was ''sucient to propose the GCR model for the
glacial cycles, [but] clearly insucient to establish it.''
Kirkby (2008) reviewed the status of the cosmic ray theory over several time
periods from the past few thousand years to hundreds of millions of years. While
he concluded that ''numerous paleoclimatic observations, covering a wide range of
time scales, suggest that galactic cosmic ray variability is associated with climate
change,'' he also admitted that there is considerable uncertainty in the mechanisms
and the significance of the effect.
This topic should alert us to the possibility that complex processes may be at
work in the Earth's climate that depend on factors seemingly unrelated to our
climate. Most recently, Agee et al. (2011) reviewed the proposed hypothesis that
''galactic cosmic rays (GCRs) are positively correlated with lower troposphere
global cloudiness.'' They emphasized that Marsh and Svensmark (2000) and
Svensmark (2007) utilized ''lower troposphere cloud cover'' rather than total
cloud cover, and this appears to be more appropriate to the theory. However,
several published papers have questioned the validity of the cloud data. Agee et
al. (2011) examined the recent period between solar cycles 23 and 24 during which
solar activity was very low, leading to ''record high levels of GCRs'' by correlating
data on GCR levels with measurements of lower-troposphere cloud cover. Figure
8.8 shows a very poor correlation between cosmic rays and clouds, which seems to
cast doubt on the GCR theory.
8.7.3 Ocean-atmosphere model
Bell and Eng (2007) published a small book in which they expounded their theory
on the origin of ice ages and interglacial cycles as an alternative to the astro-
nomical theory. Orbital variations have been around for many millions of years,
but ice ages have only been around for about 3 million years—which suggests that
the origin of ice ages does not lie in orbital variations.
Instead, they believe that the solar energy actually absorbed by the Earth is
what matters—not the small changes in solar input above the atmosphere. In their