Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 92

CAS closure ''was more conductive to North Atlantic deep water formation,'' and
that the North Atlantic warmed ''significantly'' after CAS closure, resulting in
''increased evaporation and precipitation along its borders.'' They concluded that
their results were ''consistent with the hypothesis [that CAS closure led to glaciation
in the NH] although it is not possible to completely refute or verify it on the basis of
model output.''
Lunt et al. (2008) tested the hypothesis that closure of the CAS led to NH
glaciation by using a fully coupled fully dynamic ocean-atmosphere general
circulation model with boundary conditions specific to the Pliocene, and a high-
resolution dynamic ice sheet model. They carried out two GCM simulations with
closed and open Panama seaways, and used the simulated climatologies to force
the ice sheet model. They found that the models support the Panama Hypothesis
to a modest extent, in that the closure of the seaway results in a more intense
Atlantic thermohaline circulation, enhanced precipitation over Greenland and
North America, and ultimately larger ice sheets. However, the volume difference
between the ice sheets in the closed and open configurations was found to be
small, equivalent to about 5 cm of sea level. They therefore concluded that
although the closure of the Panama seaway may have slightly enhanced or
advanced the onset of NH glaciation, it does not appear to be a major forcing
mechanism.
Nisancioglu et al. (2003) also performed interesting studies but did not resolve
the issue.
Prange and Schulz (2005) used a climate model to investigate the effect of
closure of the CAS on the climate of the NH. The model results indicate an
increase in annual mean sea surface temperatures of about 1 C in the North
Atlantic and North Pacific oceans as a result of the Panama closure.
Driscoll and Haug (1998) offered an alternative hypothesis for the onset of
NH glaciation due to closing of the CAS. They argued that closing the Panama-
nian isthmus would increase thermohaline circulation and bring enhanced
moisture supply to high latitudes, promoting ice and snow formation at high
latitudes, but the accompanying heat release would have inhibited ice growth.
Instead, they proposed a possible solution whereby enhanced moisture transported
to Eurasia would enhance freshwater delivery to the Arctic via Siberian rivers.
Freshwater input to the Arctic would facilitate sea ice formation, increase the
albedo, and isolate the high heat capacity of the ocean from the atmosphere. It
would also act as a negative feedback on the eciency of the ''ocean conveyor
belt heat pump''.
Molnar (2008) provided a critical review of the relationship between closing of
the CAS and the onset of ice ages in the NH. He concluded that the relevant
evidence can be interpreted to permit a causal relationship between them but can
also be interpreted to show no such relationship. The approximate simultaneity of
the closing of the CAS with the onset of global cooling and the first major ice
advance is highly suggestive. However, he concluded that the timing of the actual
closure has not been pinpointed. The hypothetical connection between a closed
CAS and the onset of glaciation requires profoundly different North Atlantic