Terrestrial Palaeoecology and Global Change

Chapter 7. Climate change
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nomenon brought to focus by Lorenz (1967), Lamb (1977), Zubakov (1990) and elsewhere.
Atmospheric CO 2
fluctuations are considered as an integral part – an enhancer
– of the processes (Fig. 106).
VII.7. Summary of climate change
Since climate affects both biotic and sedimentological aspects of the biospheric carbon
cycles, the proxies of climate change are countless, yet all of them potentially change
their meaning with evolution, hence ambiguous. Direct inference from indirect correlations,
as between climate and isotope fractionation, produce mythic thermal maxima and
minima (e.g., the “LPTM”: VII.5). Likewise, too much emphasis on quantification of
palaeoclimatic variables is scarcely productive. Mean global temperatures are as informative
of climatic situations as mean temperatures for a hospital are of the patient’s
conditions. Anyway, robustness of interpretation is preferable over numerical detail. Longterm
climatic evolution is better reflected by the processes of comparable rates, such as
displacements of vegetation zones (VII.4).
The geological record of past climates can be more objectively interpreted in terms of
climatic gradients rather than global means. What is recorded as a global climate change
is primarily a redistribution of heat over latitudes, with contrasting situations of (1) gentle
equatorial to polar temperature gradient and a likewise low precipitation gradient of the
opposite sign or (2) overheating of tropical zone – freezing of polar areas, with precipitation
reallocated to the polar (ice caps) and equatorial (rainforests) zones. The latter
situation is brought about by orographic barriers, such as mountain ranges over the elevated
Tethys belt. Glaciation is a global, rather than polar, phenomenon. At a high stand
of the continents correlated through rotational mechanisms (V.8) with a low-latitude
orogeny, glaciation might have commenced in the tropical highlands later spreading to
the polar lowlands.
Over the earth’s history, the first-order climatic cycles correspond to alternations of
the Tethys seaway geography with the Tethys mountain range geography. The latter is
consequential to the major pulses of the Taconian, Hercynian and Alpine orogenies correlated
with the Late Ordovician, Late Carboniferous–Early Permian, and the Plio-Pleistocene
glaciations. Their ca.180 m.y periodicities correspond to the Galactic Year (Steiner
& Grillmair, 1973). The subordinate climate cycles, down to 4-year scale, are triggered
by the earth’s rotational and orbital forcing and are amplified by the causally related
geographic and oceanographic effects.
Polar glaciations inflict temperization of mid-latitudinal climates promoting a spread
of deciduous biomes. Insofar as extensive zones of temperate deciduousness are recorded
for the greater part of geological history since the mid-Devonian (VII.4), a glacial
(mildly glacial, as at present) climate should be considered as a norm while the icefree
situations are atypical.