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change solar input to higher latitudes. Thus he claimed that, prior to about one
million years ago,
ice volume wasn't suciently high and Earth surface temperature
was[n't] suciently low to provide the extent of ice comparable to those of
the Pleistocene ice sheets. The change of glaciations mainly grouped at high
latitudes
''
...
...
in this situation was caused by rather short-period forcing of axial
tilt according to empirically found 41-kyr periodicity of these changes.''
In other words, he claims that obliquity alone affected the Earth's climate
prior to a million years ago, but this has no technical basis.
Although Bol'shakov admitted,
are perfectly
legitimate so far as the direct effects of the eccentricity are concerned, and it was
quite natural, and, in fact, proper to conclude that there was nothing in the mere
increase of eccentricity that could produce a glacial epoch,'' the essence of his
proposal is that sometime around a million years ago, the ''Earth surface tempera-
ture and glacier mass at high latitudes reached critical values'' so that the effect of
global insolation change resulting from eccentricity variation ''was sucient to
prevent melting of glaciers.'' In other words, he believes that the climate was
driven by obliquity changes prior to a million years ago, but in the last million
years it was driven by changes in eccentricity. When the global ice budget reached
a certain point, the Earth became sensitized to greater positive feedbacks as a
result of albedo and greenhouse gas per unit change in insolation. Thus, he
concluded:
''All
those conclusions
...
for the last million years the development of global glaciations [has been]
mainly determined by the simultaneous forcing of eccentricity and obliquity
variations enhanced by positive feedbacks effect against the background of the
global cooling.''
''
...
According to this model, glacial-interglacial transitions are primarily
controlled by changes in eccentricity, which alters overall solar input to the Earth,
modulated somewhat by changes in obliquity. Higher eccentricity produces a
warmer climate due to the 1
r
2
law for solar irradiance. Thus, one can compare
the time series of eccentricity with that of climate. If one compares that with
measures of ice volume, a time lag would likely be involved.
His arguments do not make sense to this writer. Had he presented them as
suggestions of a possibility, they would be received more kindly; however, his
bombastic insistence that he has the answers belies the fragility of his arguments.
=
9.7.2 The Mid-Pleistocene Transition
As
Figures 2.4
and
5.6
reveal, the fundamental character of ice age-interglacial
cycles changed during the past 2.7 million years. Whereas prior to roughly
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