Abstract
There are several methods of predicting terrestrial palaeoclimates from the
size and shape of fossil leaves (foliar physiognomy). The assumptions and
sources of uncertainty of these methods are considered and used to determine
the true uncertainty. Their ability to predict mean annual temperature (MAT)
is poor. The approximate standard errors for samples of living vegetation in
North America are in the range of 1.7˚C to 2.5˚C, but the true
uncertainty for fossil samples is higher. Specimens with very different
physiognomy to typical specimens in the model have higher uncertainties.
Besides these uncertainties, the processes of fossilisation, the allocation of
specimens to taxa, and the effects of other factors on foliar physiognomy all
increase the uncertainty of the predictions. Overall uncertainties in the
predictions of MAT are equivalent to standard errors of about 3–5˚C
depending on the nature of the fossil site and flora. Other factors affect
foliar physiognomic predictions significantly because predicted MAT does not
change as rapidly with altitude as true MAT, and floras from different parts
of the world with similar temperatures give different temperature predictions.
Mean annual temperature and one precipitation parameter (probably mean annual
precipitation or the growing season precipitation) can be predicted more or
less independently, although the predictions of precipitation are weak.
Physiognomic signals for other climatic parameters are weak or apparently
non-existent, and previously published predictions of past equability are
primarily based on correlations with modern MAT, rather than physiognomy.
Subject
Plant Science,Ecology, Evolution, Behavior and Systematics
Cited by
41 articles.
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