INTERNATIONAL JOURNAL OF CLIMATOLOGY

Int. J. Climatol. 20: 1873–1874 (2000)

BOOK REVIEW

WARM CLIMATES IN EARTH HISTORY, B.T. Huber,K.G. MacLeod, and S.L. Wing (eds), Cambridge UniversityPress, Cambridge. 2000. No. of pages: 462. Price £70.00, US$115.00 (hardback). ISBN 0-521-64142-X (H/b).

Understanding greenhouse climates and predicting the natureof future global warming is, of course, a major topic inclimatology today. In our present icehouse Earth, we usuallythink about climate warming on the scale of interglacialperiods. But to get a glimpse of what a real greenhouse worldwould be like, we have to look back into the geological past.Several times during the past 600 million years or so the Earthhas experienced climates so warm that the polar regions havebeen free of permanent ice caps, allowing the high latitudes tobe covered in lush vegetation.

This book is a collection of research papers that focus onthese warm periods in Earth history. The 14 papers deal withspecific case studies from the Palaeozoic to early Cenozoicperiods, and also with numerous climate models that attemptto simulate these past climates on the greenhouse Earth. Thebook is divided into five parts. Part one covers some of themain forcing mechanisms that produce warm climates, such asocean and atmospheric circulation, albedo, CO2, volcanic ac-tivity and continental distribution (Valdes). Recent advancesin palaeoclimate modelling are discussed by Deconto et al.;they highlight the importance of setting up correct boundaryconditions for new models, especially for ocean conditions,which are still poorly known in the past. The discrepancybetween tropical sea surface temperatures predicted by climatemodels and those determined from the geological record is afrequent topic in this book, and is highlighted by Crowley andZachos in their study of zonal temperature profiles.

The following three parts of the book are concerned withcase studies of episodes of warm climate. This is where thegeological evidence for past climates is presented, although,inevitably, climate models feature strongly too. An oceancirculation model is presented by Bice et al. that attempts topredict a three-dimensional temperature profile through theocean for the Eocene period (55 Ma). Interestingly, the modelunder-predicts ocean temperatures by 2–10°C, compared withtemperatures obtained from isotopic analyses of oceanic mi-crofossils. The prevalence of water saline water masses in deepoceans may well have been an important feature of warmclimates, as demonstrated by MacLeod et al. for the Creta-ceous period. Thomas et al. also investigated the isotopicsignals in foraminifera in warm Tertiary oceans, and proposedthat several phases of ‘hyperthermal’ events may have oc-curred during the Eocene period, during which deep oceanwaters were dominated by warm high-salinity waters from thesubtropics, causing short-term rapid climate change.

On land, a feature of a greenhouse Earth was the presenceof forests at high latitudes. Taylor et al. present spectacularlypreserved forests from Antarctica that grew close to the SouthPole during the Permian and Triassic periods. Palaeoclimatemodel results for this time period are hard to reconcile withsuch strong evidence of warmth near the poles. Deconto et al.used general circulation models (GCMs), coupled with a vege-tation model, to simulate polar vegetation during the Creta-ceous period. To maintain polar forests, they had to use CO2

levels over four times the present day values, as well as greateroceanic heat transport; any less than this, and tundra condi-tions were predicted.

Fossil plants are a major source of information for terres-trial palaeoclimates. Leaf margin analysis of angiosperin fos-sils, used by Wing et al. to estimate temperatures for Eocenewarm climates in mid-North America, showed an unusualphase of a rapid climate change of short-term cooling andwarming, lasting for about 1–2 million years, although thecause of such short-term events is not clear. For pre-Creta-ceous times, before flowering plants had evolved, interpretingclimate from plant evidence is more difficult. However, Rees etal. present a new multivariate statistical method for determin-ing global climate zones and biomes by linking foliar morphol-ogy with palaeoclimate evidence. The results provideimportant new information to test climate models for theJurassic period.

A major feature that is hard to specify in climate models ismountains, especially their location and elevation. Norris et al.discuss ways in which mountains can influence climate, andpropose a new method for estimating palaeoaltitude, usingpalaeobotanical and isotopic data; they then used this toestimate the elevation of the Laramide mountains in theEocene period. Finally, studies of warm climates from wayback in the Palaeozoic period are presented here, including astudy of palaeontological and isotopic data for the Devonianof North America by Murphy et al., and that of the Ordovi-cian (440 Ma) glaciation that occurred within a greenhousephase. This was a short cold snap, lasting for less than 1million years. The Earth was probably teetering at an ice-free/glacial threshold, according to Gibbs et al., and, although CO2

levels may have been as high as 14 times as they are at present,a rapid drop in CO2, caused by a dramatic increase in oceanicproductivity, may have been enough to plunge the Earth intoa short-lived glaciation.

The book ends with an excellent review by Crowley of therole of CO2 in climate change during the geological past. Hestresses, however, that other factors must also be taken intoaccount, most importantly, solar luminosity and land-sea dis-tribution, and, to a lesser degree, mountains, vegetation andocean heat transport. The clear message coming through fromthese papers is that much more basic geological data is re-

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BOOK REVIEW1874

quired to rigorously verify the many model simulations thatare produced these days. Crowley also pleads for more explicitdiscussion of the uncertainties in estimates from palaeoclimatedata, and more statistical evaluations of computer models inorder to improve our understanding of past climate change.

This book is intended as a research text, and certainly, it isa book that no palaeoclimatologist should miss. It containssome excellent overviews of palaeoclimate methods, and someclear explanations of climate models. It also, however, presentssome pretty specific data for selected case studies that wouldnot be easy-going for undergraduates or the non-specialist.Many (but not all) of the papers start with abstracts and end

with excellent summaries, which are invaluable for highlight-ing the main points of each. For climatologists who study themore recent past, this book will provide an excellent insightinto the problems that climate modellers have to address withgeological data, and the mechanisms that were important increating true greenhouse climates on an ice-free Earth; inshort, the existence of such globally warm climates that we canonly dream of.

JANE FRANCIS

School of Earth Sciences, Uni6ersity of Leeds, UK

Copyright © 2000 Royal Meteorological Society Int. J. Climatol. 0: 000–000 (2000)