Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 83

The data on temperature and CO 2 over hundreds of millions of years are far
less reliable, and conclusions drawn from these time periods are dubious at best.
Our conclusion here is that CO 2 is probably one of several major factors in
long-term climate change, but other factors such as the placement of the conti-
nents on Earth, the functionality of ocean currents, the past history of the climate,
the orientation of the Earth's orbit relative to the Sun, the luminosity of the Sun,
the presence of aerosols in the atmosphere, volcanic action, land clearing, bio-
logical evolution, etc. are also important. Hence, there is probably no single curve
relating global average temperature to CO 2 concentration but, rather, a set of
curves that depend on the above factors.

2.4 CONTINENTAL DRIFT AND CONTINENTAL GEOMETRY AS A
FACTOR IN PALEOCLIMATE CHANGE

2.4.1 Effects of continental geometry

Since the general acceptance of the continental drift theory, it has been widely
surmised that changing continental geometries likely contributed to long-term
climate change. However, it is not exactly clear how this occurred. ''Continents
are important to climate for three main reasons: they are a platform upon which
polar glaciers can form; they are the primary sites of the silicate weathering reac-
tion that governs atmospheric CO 2 (the amount of weathering is strongly affected
by the continental configuration); they affect the geometry of ocean basins and,
hence, the ability of oceans to transport heat from one latitude to another''
(Pierrehumbert, 2009). Dietz and Holden (1970) provided a good description of
the continental drift process. Campbell pointed out:

...

at certain times in the past, the equatorial ocean currents were able to
circulate the Earth. This allowed more warming because of a much higher rate of
ocean re-circulation and currents diverging from the equator to the north and
south would be warmer. Equatorial flows at other times have been blocked
resulting in higher latitude currents forming circumpolar currents. This isolates
the polar continents and causes polar temperatures to drop.''

''

Frakes and Kemp (1972), Sellers and Meadows (1975), Kennett (1977),
Ravelo et al. (2004), and many others have discussed the effects of continental
drift on climate.
Several studies have been carried out using climate models to estimate the
effect of hypothetical landmass distributions on global climate. However, none of
these is entirely convincing. Nevertheless, without using climate models, we can
draw a few conclusions in this regard.
The albedo of snow/ice cover may be as high as 0.9. The albedo of land
depends upon the nature of the land (forest, desert, plains, etc.) but on average it
is probably something like 0.35. The albedo of the oceans is probably about 0.1.
The net albedo of the Earth depends on a global average of all land and ocean