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Figure 9.12. Comparison of peak solar intensity in summer with a horizontal surface above the
atmosphere at 65 N and 65 S over 400,000 years.
clearly shows, total annual solar input hardly varies from year to year. Hence,
peak solar intensity in summer seems to be a much more likely candidate. A few
have claimed that it is the variability of solar input in local winter that is most
important, but that makes no sense because there is hardly any solar input to high
latitudes in winter. How could the variability of a small amount have any effect?
Bluemele et al. (2001) pointed out that a 50-year glacier mass balance study in
Sweden showed that it was the summer temperature that determined the extent of
the glacier. Some believe that it is solar input to the south affecting ocean currents
that produce climate change in the north. In addition, there are theories that
climate change emanates from changes in the tropics.
Despite the extensive literature on the astronomical theory, there is an
appalling lack of modeling the specifics of how solar variations produce extreme
climate change. Perhaps that can be excused to some extent because of the
extreme complexity of the issue. However, if this is the case, how can so many
scientists reach firm conclusions as to the veracity of the astronomical theory?
The astronomical theory is actually little more than a high-level belief that solar
variations affect climate. Exactly how these variations affect climate remains
uncertain. A few models have been developed but none of
these are very
satisfying—at least to this writer.
While credible mechanisms for the processes by which solar variability affects
climate are not available, one may hope to gain an understanding of them by
comparing the curves of peak solar intensity in summer (from the previous
sections) with isotope data from ice cores and ocean sediments. The situation here
is somewhat akin to that of a detective trying to solve a crime by examining clues.
Two approaches have been taken.
In one approach, solar variability and isotope data are both analyzed
 
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