Climate, History and the Modern World

Hubert H. Lamb

• Publisher: Routledge
• Year: 2002
• Print ISBN: 9780415127349
• eBook ISBN: 9781134798384
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Geography
• Index: Geography

We live in a world that is increasingly vulnerable to climatic shocks - affecting agriculture and industry, government and international trade, not to mention human health and happiness. Serious anxieties have been aroused by respected scientists warning of dire perils that could result from upsets of the climatic regime. In this internationally acclaimed book, Emeritus Professor Hubert Lamb examines what we know about climate, how the past record of climate can be reconstructed, the causes of climatic variation, and its impact on human affairs now and in the historical and prehistoric past. This 2nd Edition includes a new preface and postscript reviewing the wealth of literature to emerge in recent years, and discusses implications for a deeper understanding of the problems of future climatic fluctuations and forecasting.

1
INTRODUCTION

Most generations of mankind in most parts of the world have regarded climate as an unreliable, shifting, fluctuating thing, sometimes offering briefly unforeseen opportunities but at other times bringing disaster by famine, flood, drought or disease—not to mention frost, snow and icy winds. Before the days of records and reference books with figures for past years, there could hardly be any clear perception of trends. In old writings, including those by fine observers such as John Evelyn and Samuel Pepys, we come across too frequent references to such items as ‘the severest winter that any man alive had known in England’, ‘so deep a snow that the oldest man living could not remember the like’, and so on. Yet here and there we do find recognition of long-lasting changes. There was no mistaking this when the glaciers in the Alps, in Iceland and in Norway, during the seventeenth century and thereabouts, were advancing over farms and farmland. Doubtless, the nomadic peoples of the past or present in every continent have been aware of such changes at times when their pastures were drying up. It must have been equally clear, at least to some, when in various countries in the late Middle Ages traditional crops and croplands had to be given up and taxes ‘permanently’ reduced. When, on the other hand, the climate becomes warmer or more convenient for human activities, it tends to be taken for granted and the change may for a long time pass unnoticed. A probably rare awareness of a change of this sort occurs in a passage in the ancient Roman horticultural work De Re Rustica (Book I) by Columella, citing a statement by ‘the trustworthy writer Saserna’ in the early part of the first century BC that ‘regions [in Italy] which previously on account of the regular severity of the weather could give no protection to any vine or olive stock planted there, now that the former cold has abated…produce olive crops and vintages in the greatest abundance’. In another situation much later in history we may detect a slowly dawning awareness, possibly in very vague form, of a climatic change when the vineyards of medieval England, some of them cultivated for hundreds of years, were given up after many years of dismal failure.

Yet for eighty years or more, down to about 1960, it was generally assumed that for all practical purposes and decisions climate could be considered constant. This view seemed at the time to be soundly based in science; the first long series of regular meteorological observations made with instruments in the cities of Europe and North America showed the climate of the late nineteenth century to be very similar to the period about a hundred years earlier when the observations had been instituted. Many working practices in applying climatology to forward planning are, for better or for worse, still based on this assumed constancy of climate. Everyone will agree that if climate were defined by the statistics of weather over a sufficiently long time, it would be effectively constant. But how long would this period have to be? If we were to take the conditions of the last million years as a basis, the repeated swings from ice age to warm interglacial conditions and back again would have to be regarded as part of the normal climate. Yet the changes would be sufficient to wreck the economy many times. The practical choice, a definition relevant alike to our individual concerns and to national and international affairs, is surely to consider that the climate has changed if the conditions over some large part of a human lifetime differ significantly from those prevailing over an earlier or later period of similar duration.

We live in a time of renewed perception of climatic and environmental change. For many people this arises from fears about the possibility that mans activities, and their increasing scale and variety, may have side-effects that disturb the climatic regime, just as they are visibly changing other aspects of the environment about us. Others may be interested in the possibility of using the increasing power of our technology deliberately to modify the climate: for instance, to increase the total cultivable area of the world or, sad to say, to change the pattern of climate as a possible strategy of war. In any case, many people now know that there have been significant shifts of climate during the twentieth century: at first, a more or less global warming to about 1950, then some cooling. More recently, a notable increase in the incidence of extremes of various kinds in almost all parts of the world has hit agriculture and created difficulties for planning in many fields.

The former assumption of constancy of climate is thus widely felt to be unsatisfactory today. And, after many decades in which there was little or no inquiry about climatic development and change, the leading institutes of meteorology and climatology are now pressed for advice on future climate. The position is doubly unfortunate in that the forecast opinions ventured by the ‘experts’ have often increased the confusion, the views of the theoreticians sometimes contradicting those whose study has been concentrated on reconstructing the actual past behaviour of the (natural) climate.

The assumptions that were common until recently among knowledgeable people outside the sciences of meteorology and climatology are well illustrated by Jacquetta Hawkes and Sir Leonard Woolley writing in volume 1 of the UNESCO History of Mankind (London, Allen & Unwin, 1963). After recounting the drastic changes of the ice ages, interglacials and early postglacial times, they stated

by about 5000 BC when the first agricultural communities were already extending in Asia, the climate, the distribution of vegetation and all the related factors had settled to approximately their present condition. When true civilization at last began, not only was Homo Sapiens and the agricultural basis of his existence firmly established, but the natural environment which was to form the background of all subsequent history had already assumed the form which we ourselves have inherited.

Most archaeologists today realize that climate and environment have a more interesting history than that.

In reality, during our lifetime and that of the structures which we build, the climate is always changing to a greater or less degree. And the landscape that goes with it, the ranges of vegetation and of the animal species, birds and insects that inhabit its provinces, change too—mostly rather slowly but sometimes more quickly. The changes in these realms are on the whole more gradual than the swings of weather and climate which instigate them, but they also undergo their disasters and depopulations, recoveries and advances. This book, besides introducing the evidence on which past climate can be reconstructed, presents the story of this continual ebb and flow and of the more lasting shifts of climate. We shall see in outline how these changes happen continually and how the fortunes of the flora, fauna and human populations are forever being affected. Just how some of the impacts work will be examined in more detail in chapter 15.

It is true that, as Jacquetta Hawkes and Leonard Woolley put it, for many thousands of years the zones we know have been present and identifiable somewhere on this planet, ‘the jungle has been there for the pygmy, the grassland for the nomad or the cultivator, and the ice-floes for the Eskimo’, but the movements of their margins have caused much trouble from generation to generation and continue to do so. In looking for evidence of climatic impact in the course of history, it is sensible to look most at the marginal areas near the poleward and arid limits of human settlement and activity, for it is there that vulnerability is likely to be greatest. In regions like the lowlands of western and southern Europe most of the effects of climatic changes are liable to be obscured by successful competition of the societies living there with the inhabitants of regions more adversely affected.

Often people think about history (and some historians have written about it) as if it were basically a tale of the deeds of great men and women. These heroes and heroines, the causes which they led, and the crises and battles which resulted, are commonly thought of as having determined the structure of society in the times that followed. Of course, economic crises arose from time to time and had some influence on the course of events. But many aspects of the economy, and the landscape which developed with it, have been largely seen as products of great decisions and decisive battles. Alternatively, from the Marxist view of history it is all a question of the development of man’s technology and the tools which at any given time were at his disposal to conquer and exploit the world about him. The assumption that the climate, the opportunities which it offers and the constraints it places upon man and the environment are effectively constant generally underlies all these views.

Some readers may at this point decide that the interpretation of history in these pages is but a resurrection of climatic determinism, an over-simplified view which they rejected long ago. Such labelling only tends to restrict freedom of thought. Who can deny that there are cases when a desert or a marsh, an ice-cap or a glacier, or indeed the sea, has advanced over land that had been settled and used for agriculture; and in these extreme cases there is no doubt that a climatic change, or the accumulating consequences of some tendency of the climate over previous years, has dictated human action. Most situations are, of course, far more complex and allow the human populations some choices. But, even in many of these, to write history without reference to the record of climate is to make matters more obscure than they need be and may amount to making nonsense of the story.

Progress towards understanding inevitably has its difficulties. Some historians of yesteryear who were interested in the possible impact of climate were not helped by inaccuracies that were probably unavoidable at the time in the first reconstructions of the climatic sequence during the centuries before meteorological instrument records began. But the last thirty years or more have seen great advances in the quantity and variety of evidence of past climate and in the methods available to interpret the evidence. Gradually, we are gaining a more reliable record of the climate, the main features of which have already been corroborated by independent data and methods.

When we compare this record with the course of human history and the still longer record revealed by archaeology, we cannot fail to be struck by the many coincidences of the more catastrophic events in both. This again raises the question: what exactly was the role of climatic disturbance in the human story in each case? It will certainly be difficult, and may be dangerous, to generalize. There is room for many detailed investigations to improve our understanding. But, in general, it seems helpful at this stage to think of climate as a catalyst or at the least a trigger of change: in the major breakdowns of societies and civilizations climatic shifts may often be found to have played the role of a trigger, rather like the recently recognized trigger action of the variations of the tidal force in setting off earthquakes and volcanic eruptions.

Historians and others have also been confused and uncertain as to how far changes of climate and environment, some of which have had an impact on history, could have been caused by human activities. Many people in every part of the world today, including those who are generally well informed (and among them some meteorologists), are plainly predisposed to the opinion that if the climate is not as constant as we used to think it, this must be due in some way to the impact of man. The impact of human activities on other aspects of the environment is only too obvious and began at least as far back as the first clearance of forests for setded agriculture thousands of years ago. And, with the now rapidly growing scale and power of our technology, new possibilities of effects upon the climate—whether intentional or inadvertent—must in all reason be watched for.

Both human history and the history of climate are often thought of as cyclic, as if we are all caught in a wheel of fate whose turning is not only remorseless but knows no intelligible causes. In these pages an attempt is made to understand rather more about these variations. We shall see the workings of nature, and latterly some possible intrusions of man, in the continual development and fluctuations of climate. And we shall observe how these break in upon the course of human affairs.

By now, it is clear that the only approach that is likely to be profitable to the hints of cyclic recurrences in climate is to seek to identify the evolutions in the atmosphere, oceans and terrestrial or extraterrestrial environment which mark— and in some cases cause—their successive phases. In this way we may come not only to understand the physical processes which lead from one phase to the next, and what controls or varies the timing, but ultimately to discern the origins of the whole sequence. One example, illustrated in chapter 4, is the sequence which typically follows a great volcanic eruption and leads to the formation of a persistent dust veil in the stratosphere. It is equally clear that there are various cycles in human affairs, whose causes also need to be understood. Some of these are linked to cyclic phenomena in climate and the environment. Others certainly are not. The cycle of day and night is linked with variations in the death rate and in the incidence of criminal and other activities, some of which disturb the peace. Next in the scale, the seasonal round of the year and each years seed-time and harvest mark out times when peoples health and energy are commonly at their best, times when the stresses of dearth, undernourishment and starvation are most likely, times when travel is easiest and times favourable for military adventures. Operating over a longer time-scale covering a few years, we observe cycles of confidence in business activity, the trade cycle, and, similarly, the swings of the political pendulum which seem not to be wholly masked even in totalitarian states. Over longer periods, ranging from one generation to several centuries in length, we observe swings from strong or dictatorial rule to democracy, too often gradually degenerating into muddle and chaos, followed by dictatorship again. And in the realm of moral and social life and family discipline we also see oscillations as each generation, in establishing its independence, veers off from the ways of its predecessor, often thereby turning once more to some of the habits of earlier generations. And there are those like Arnold Toynbee who believe that the mere ageing (or ‘wearing out’) of human institutions is sufficient in the course of time to bring down civilizations. In all these cases, however, as with the cycles in climate, some external event may cut the cycle short and start a new train of events. Thus, climate and human history present not wholly independent but partly interactive systems. It should be worth while to trace cause and effect in the linkages and certainly to look for any regularities.

One of the least happy lessons of human history may be read between the lines of the late medieval decline in Europe from the genial climate of the high Middle Ages which coincided with the twelfth and thirteenth century climax of cultural development and energetic activity. When former croplands were failing and being abandoned in the north and on the uplands of Europe (and also, as we now know, in the Middle West of North America), when farms and villages were being deserted and fields enclosed for sheep, in the riots and revolts which followed blame for all the sufferings and troubles was fastened on those who (for whatever motives) were in fact turning land to new and more productive use. Is it too much to hope that with better understanding of the behaviour of climate, accompanied by some wise preparations and sympathetic explanation to the people affected, we may cope better with such tensions in the future? Is it always appropriate when things go wrong to ask whose fault it is?

Some advance in sympathy, which we like to think characteristic of our own century, was registered by a speaker in a BBC religious affairs broadcast (‘Thought for Today, 21 July 1978) who said: ‘Who is responsible for mass unemployment….Who is responsible for the world recession? …the answer must be us.’ Such speaking is suited well enough to awaken our moral responsibility for one another throughout the world community, but the case in reality demanded some allowance for extremes of weather in the 1970s, for extensive crop failures, as in 1972 (and 1975), and their effect on world grain stocks.

This book provides an introduction to the development of climate, the record of its vicissitudes and their impact on the affairs of mankind. Human history is not acted out in a vacuum but against the background of an environment in which many sorts of change are always going on: besides the changes imposed by man, a never-ending competition goes on among the species of the plant and animal worlds, whose fortunes, like those of the soil and of the physical landscape itself, are continually affected by the vagaries of the climate. Some of the changes are slow and gradual, others are sharp and register abrupt events. We shall see examples of all these things.

The next three chapters are necessarily concerned with the physical basis of climate and climatic changes, with just enough illustrations to provide an adequate picture of the behaviour of this changing background to human life. In the rest of the book the history and development of climate in the past and in our own day are presented interwoven with allusions to aspects of human affairs and to other changes in the environment where the effects of climatic vicissitudes are registered.

We shall see that, contrary to the thinking of a generation ago, mankind is by no means emancipated by science and the technological revolution from the effects of climatic changes and fluctuations. Vulnerability to the effects, which included great famines in the past, seems rather to be increasing once more after some decades when a degree of immunity had indeed been achieved. Exposure to risks attending climatic shifts is increased greatly by the population explosion and the difficulty of producing enough food. The situation is made worse by the demand for an ever-rising standard of living in all parts of the world. And the systematic exploitation of resources to the limit, especially in agriculture, maximizes the risk.

It is reported (e.g. by Professor R.W.Kates of Clark University, Worcester, Mass., at the World Climate Conference held in Geneva, 1979) that threequarters of the estimated world total cost of $40 billion yearly from natural hazards is accounted for by the major climatic causes of disaster: e.g. floods 40 per cent, tropical cyclones/hurricanes/typhoons 20 per cent, drought 15 per cent. The national and international organization of our present civilization with its advanced technology undoubtedly enables us, as never before, to rush help and supplies to relief of the immediate distress caused by natural disasters. It may be doubted, however, whether this complex world-wide community, with its interlocking arrangements and finely adjusted balances, is any more able than its predecessors to absorb the effects of long-term shifts of climate—particularly if they come on rapidly —entailing significant geographical displacement of crop zones and areas suited to various kinds of food production or are accompanied by mass migration of people.

It is important therefore to seek better knowledge of the pace of climatic change, especially the more rapid and drastic events of climatic history, and to identify the early symptoms which may have signalled the changes. On the other side, study must be given to the flexibility needed in the organization of human society if we are to be able to adjust to such things.

2
THE CLIMATE PROBLEM

CLIMATE DEFINED

By climate we mean the total experience of the weather at any place over some specific period of time. By international convention the period to which climate statistics relate is now normally thirty years, e.g. at the time of writing 1941–70, although we shall see arguments for preferring different periods for different purposes, particularly somewhat longer periods, such as fifty or a hundred years, and for preferring (as our grandfathers did) the decades that correspond to our linguistic usage based on our system of numbers, e.g. 1940–9…1970–9, and so on.

Climate was sometimes wrongly defined in the past as just ‘average weather’: the statistics required to specify a climate comprise not only averages but the extremes and the frequencies of every occurrence that may be of interest. The Classical Greek word μ originally referred to a zone of the Earth between two specific latitudes, being associated with the inclination of the sun; and hence it came to be associated with the warmth and weather conditions prevailing there. This association was still embodied in the word ‘clime’ when first used in English in the sixteenth century and for long after. It was commonly used to refer not only to the prevailing climate as we mean it but to the terrestrial environment, vegetation, etc., that goes with that.

Climate has been too much taken for granted in recent times. Since some time in the late nineteenth century it has been usual to suppose that for all practical decisions climate can be taken as constant, however obvious the year-to-year fluctuations may be. The latter seemed best treated as random in their occurrence, although a few shadowy cycles might play a part in them and perhaps be of some limited use in forecasting, e.g. to indicate which was likely to be the finest European summer in a decade or to predict the years of high or low level of the great east African Lake Victoria. Anyway, such forecasts often failed. It was known that ice ages had occurred in the distant, ‘geological’ past; but the climate in Roman times seemed to be not too much different from now, and it was assumed that this must be true of all the centuries in between.

As we shall see in later chapters, those centuries in fact brought a succession of changes in Europe and elsewhere which included a long period of evidently genial warmth in the high Middle Ages followed by the development world-wide of a colder climate, especially in and around the seventeenth century, with probably the greatest spread of ice since the last major ice age. Such a sequence can hardly have been withstood by the primitive human economies of those times without effects on their history.

EARLY WRITING ABOUT CLIMATE AND HISTORY

By coincidence, many writers at the time of this Little Ice Age and some of the early scientists then living were much interested in what has become known as the ‘climate theory’ of the ‘humours’ and character tendencies of the various peoples of the world. This is a theory which goes back at least to Hippocrates and ancient Greece. Aristotle had described the ‘natural character’ of men respectively in the cold, warm and middle zones of the Earth, and so arrived at a basis for believing in the superior quality of the Greeks of his time (the Hellenes) which should fit them to rule the world if only ...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Illustrations
• Tables
• Acknowledgements
• Preface
• Preface to the Second Edition
• 1: Introduction
• 2: The Climate Problem
• Part I: The Development of Climate
• Part II: Climate and History
• Part III: Climate in the Modern World and Questions Over the Future
• Notes
• Suggestions for Further Reading
• Additional Further Reading for the Second Edition