Terrestrial Palaeoecology and Global Change

Chapter 7. Climate change
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VII. CLIMATE CHANGE
Climate basically reflects a heating of atmosphere by solar radiation reaching the
earth. The amount of heat captured by the atmosphere varies with solar flux and albedo,
while distribution of heat over the globe is controlled by a variety of orbital and geographic
factors, including sea level, relief, vegetation, etc., with feedbacks. A climatic theory is
an explanation of differential heating and its change over time, verified by the records of
various climate-bound phenomena. The greenhouse effect is one of such explanations
(Budyko et al., 1985, 1986; Berner, 1990, 1991,1997), its predictive value depending on
its consistency with the recorded climate change.
Although it is well known that climate is a system rather than a sum of quantifiable
variables, the present-day climate is traditionally depicted as such. And the same is
expected of palaeoclimatic reconstructions. To meet such expectations a palaeoclimatologist
must find in the fossil record what is not there, for what is recorded is climate
rather than climatic variables.
VII.1. Proxies
Our everyday experience relates to weather. Climate is deduced rather than experienced.
Likewise, only transient states of atmospheric air or water masses are recorded
by whatever palaeoclimatological techniques. However, the processes reflecting a longterm
climatic influence, such as vegetation changes, may prove more informative than
those under a short-term climatic control, such as isotope fractionaniton.
Climatic reconstructions are commonly conceived of as quantifications of past climates
based on some recorded phenomena adequately reflecting the non-recorded climatic
variables, serving as substitutes, or proxies, of the latter. Such climatic indicators
as leaf dimensions or isotope ratios are quantifiable, but their identification with climatic
variables can be misleading: none of the “proxies” is unequivocally related to one and
only one climatic variable, be it temperature, precipitation or seasonality.
For instance, the oxygen isotope ratios in marine carbonates of skeletal structures are
widely used in palaeoclimatology as numerical values allegedly convertible into palaeotemperatures.
It is well known, however, that biochemical isotope fractionation is controlled
by a complex system of environmental variables, including temperature. Hence the advantages
of quantification are illusionary.
VII.1.1. Lithologies
The widely used sedimentological correlates of palaeoclimates are glaciogenic deposits,
coal, redbeds, evaporites, lateritic palaeosols and a few other lithotypes confined