Geoscience Reference
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Figure 2.38. Dependence of temperature on latitude for three hypothetical distributions of
landmass.
Warm wet landmasses located in the tropics enhance the uptake of CO 2 by
silicate rock weathering. An additional factor is the placement of the landmasses.
If they are conjoined, the humidity in the interior is likely to be low, thus reducing
CO 2 uptake by the land. Conversely, if the land is distributed as separate bodies
with close access to moisture from nearby oceans, CO 2 uptake by tropical land-
masses is enhanced. Thus, the CO 2 concentration in the atmosphere can undergo
wide variations over geologic time as continental drift rearranges the continents.
This will affect global climate via the greenhouse effect.
In one study of note, two idealized continental geometries based on present
day total land area were analyzed with a climate model: (1) a tropical land belt
17 Nto17 S and (2) polar land caps from 90 to 45 N and S (Barron, 1984). The
polar land cap model was subdivided into two subordinate cases, one of which
was unconstrained, and the other had imposed a thin permanent snow cover from
70 to 90 N and S. The resultant temperature profiles vs. latitude are shown in
Figure 2.38 . Note that the modeled profile for polar landmass with snow is similar
to that which exists today.
Smith and Pickering (2003) proposed what they called a ''unifying explanation
for the four major icehouses during the past 620 million years.'' All four ice-
houses developed when a large continent lay within or less than 1,000 km from
one or both geographic poles but there have been periods when a polar continent
such as Antarctica has not been glaciated. Thus a polar or sub-polar position for a
continent appears to be a necessary (but not sucient) condition for widespread
glaciation. High topography has also been invoked as an important factor. Other
important factors for establishment of continent-wide ice sheets are the opening of
high-latitude gateways and the closing of subtropical gateways. However, whether
the changes in circulation lead to increased snow and ice accumulation in
high-latitude regions depends in part on the strength of the contemporaneous
circumpolar circulation. The problem is complex and requires numerical modeling.
 
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