Geoscience Reference
In-Depth Information
6.3 ESSAY: Post-glacial climates in the Northern
Hemisphere
Gregory A. Zielinski, University of Maine
6.3.1 Introduction
A commonly presented statement about the nature of NH climate following
deglaciation is that climatic conditions have not changed greatly with time.
This statement is only appropriate in a relative sense, because the many high-
magnitude and rapid changes in climate during the last glacial period (i.e.
Dansgaard-Oeschger Events; Figure 6.1 ) overwhelm the fluctuations that
occurred since the Earth moved into the present interglacial period. Greatest
evidence for the rapid climate change events during the last glacial comes
from the very highly resolved climatic records available from the Greenland
Ice Sheet ice-coring projects of the early 1990s (GISP2 and GRIP; American
Geophysical Union 1998 ). However, detailed evaluation of the post-glacial
record (i.e. the Holocene) in these same ice-core records (Figure 6.1 ), as well
as in other types of proxy data, shows a great deal of variability in NH climate
since the retreat of the large ice sheets. This variability becomes even more
pronounced from a spatial perspective, as once the climatic impact and
feedback mechanisms associated with large ice sheets are reduced and ulti-
mately eliminated, post-glacial climates in the NH became very regionalized.
Given such regionalization, a simple description of Holocene climatic con-
ditions from a northern hemispheric perspective is not easily attained.
Nevertheless, there is evidence that factors which control Holocene
climate in the NH operate on a roughly periodic time scale. As a result,
there is an overarching theme to changes in climatic conditions over the last
11 500 years that provides, at least, a partial sense of consistency in Holocene
climate. However, the magnitude of these changes is not necessarily the same
for each event. Similarly, the way climatic conditions respond to changes in
forcing factors through the Holocene varies, and thus the nature of the signal
in proxy records for the same event may vary. This scenario further reflects
the regionalization of post-glacial climate in the NH.
This essay summarizes post-glacial climatic conditions in the NH from a
broad perspective with the beginning of post-glacial conditions chosen to be
the end of the Younger Dryas or about 11 500 calendar years ago (e.g.
Mayewski et al. 2004 ). The reason for taking the broad perspective approach is
that there are many detailed and specific records of Holocene climatic change
that would require much more explanation and space than available in this
essay. Consequently, to give the best overall perspective on climatic condi-
tions, a general summary of overall NH climatic conditions through the
Holocene is presented, thereby highlighting the periodic nature of climatic
 
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