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Second Edition

By H.H. Lamb

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, Hubert Lamb explores 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 second edition incorporates important new material on: recent advances in weather forecasting, global warming, the ozone layer, pollution, and population growth.

Providing a valuable introduction to the problems and results of the most recent research activity, this book extends our understanding of the interactions between climate and history, and discusses implications for future climatic fluctuations and forecasting.

H.H.Lamb is Emeritus Professor in the School of Environmental Sciences and was the Founder and first Director of the Climatic Research Unit at the University of East Anglia.

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Post by thelivyjr »


We live in a world that is increasingly vulnerable to climatic shocks.

After some decades in which it seemed that technological advance had conferred on mankind a considerable degree of immunity to the harvest failures and famines that afflicted our forefathers, population pressure and some other features of the modern world have changed the situation.

In the years since about 1960, moreover, the climate has behaved less obligingly than we had become used to earlier in the century.

And there is alarm about how man’s activities might inadvertently upset the familiar climatic regime and therefore disrupt the food production which is geared to it.

This concern has in recent years largely replaced the debate which had begun earlier about the possibilities of deliberate action to change world climate so as to increase the total cultivable area.

Serious anxieties have been aroused by respected scientists, acknowledged as experts in the field, warning of dire perils: that the next ice age may be now due to begin, and could come upon us very quickly, or that the side-effects of man’s activities and their ever-growing scale may soon tip the balance of world climate the other way and for a few centuries produce a climate warm enough to melt the Greenland and Antarctic ice-caps, raising the sea level and drowning most of the world’s great cities.

This book examines what we know about climate, and its impact on human affairs now and in the historical and prehistoric past, and how we may better understand the problem of climatic fluctuations and changes.

Climatic forecasting in the strict sense may be far off, though premature claims are made from many sides.

But much has been learnt about the laws which govern the behaviour of climate.

We are already in a much better position than previous generations to understand the past and assess our present situation, so as to make more rational provision for the future than our forefathers could.

Many parts of the world have experienced more extremes of weather of various kinds in the last fifteen to twenty-five years than for a long time past and have suffered losses, which have affected political decisions and managerial decisions in industry and land-use.

Energy problems are also involved.

In these and other ways climate and our understanding of it are very much part of the problems of the modern world.

The writer hopes that this book may serve as a guide to the present state of knowledge and the potential capacity of science in these matters, and also that it may provide some helpful insights now to those on whom the burden of weighty decisions falls — affecting practical matters in agriculture and industry, government and international trade, not to mention human health and happiness.

H.H. Lamb September 1981

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Post by thelivyjr »


Since this book was published in 1982 its subject has been continually in the limelight and research has been active.

Also, as is by no means unusual, further noteworthy weather events have been in the news.

Some additional reports, remarks and comments have therefore become desirable, yet the main body of past historical work is still not well known.

It has therefore been decided to issue this revised text which incorporates notices of much new, important, material, thus making our knowledge of the past — particularly the interactions between climate and history — more accessible and providing a handy introduction to some of the problems and results of ongoing research.

Some of the climatic problems affecting humanity arise perhaps more fundamentally from the pressures of the burgeoning human population of the world than from climate.

But climate has been the trigger — repeatedly in recent years — for natural disasters such as famines in Africa and typhoon floods killing large numbers in Bangladesh.

The wars in Iran and Iraq as well as some of the outbreaks of violence in Korea, China, Vietnam and Cambodia a few years earlier may usefully be considered in relation to climate as well as man-made stresses.

Anxieties about the possibility of drastic warming of world climates resulting from the continual build-up of carbon dioxide (and other intrusions) in the atmosphere due to human activities have been forced upon the notice of politicians and industrial managements.

Even more urgently the discovery of serious damage to the protective ozone layer in the stratosphere, exposing us all to lethal amounts of the sun’s ultra-violet radiation, demands attention, including some reversal of widely popular human habits.

In these years there has also been a succession of very great volcanic eruptions that have loaded the atmosphere with debris and, perhaps more importantly, with gases and vapours that veil the sun’s radiation and may be interrupting or even reversing the tendencies towards warming of world climates.

One eruption, that of Mount St Helens in 1980 in the western USA, has forced us to note how limited must be the usefulness of applying statistically based rules of thumb connecting measures of the magnitude of any eruption with the climatic effect: for the main thrust of ejected material on that occasion was nearly horizontally, very much less being directed to the stratosphere.

There have been very notable advances in these years in weather forecasting by mathematical models, enormously improving the forecasting for up to five to seven days ahead.

But much of the gain is jeopardized by modern tendencies to use sloppy and inappropriate language in forecasts.

Thus, it is now fashionable to speak of ‘best temperatures’ in forecasts rather than ‘highest’ or ‘lowest’ whichever may really be best for the activities in prospect.

And forecasters in southern England seem to like to assume that summer temperatures in England are much the same as in the Mediterranean, or if they are not, they should be and it is a bad year.

The idea of climatic change has at last taken on with the public, after generations which assumed that climate could be taken as constant.

But it is easy to notice the common assumption that Man’s science and modern industry and technology are now so powerful that any change of climate or the environment must be due to us.

It is good for us to be more alert and responsible in our treatment of the environment, but not to have a distorted view of our own importance.

Above all, we need more knowledge, education and understanding in these matters.

Hubert Lamb Holt, Norfolk December 1994
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Post by thelivyjr »


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.

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Post by thelivyjr »



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 κ κκμ κ 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.

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Post by thelivyjr »



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 they could be united among themselves.

This was a dangerous theory, which each nation soon took up in whatever form was most flattering to its own ego, thus contributing to the heady growth of chauvinism in the seventeenth century.

It lingered on into some of the fanatical nationalisms of the twentieth century.

Theatre audiences in Shakespeare’s time loved presentations of foreign parts with overdrawn stereotypes of the peoples who inhabited them, a taste no doubt engendered by the Age of Discoveries.

Seventeenth-century English Protestant preaching had much to say about the immoral peoples of the Catholic south of Europe, whereas the northern nations were considered ‘dull and lumpish’: there was some concern therefore over the actual latitude of England!

One English writer — harmlessly enough — attributed his country’s vaunted sense of humour to the climate ‘and our gross diet’, whereas another justified the immorality of the Restoration theatre as needed to disperse the spleen and gloominess of mind to which ‘the British climate, more than any other’ made men liable!

Scientists were naturally concerned with the theory, and whatever grain of truth might be in it, only as a step towards understanding the truth about mankind.

Clearly there were problems: how was one to understand the ‘barbaric’ state of contemporary Greece and the lapsed state of Italy since its days of classical order and power?

And what of the disappearance of the free democratic ways of the early Germanic peoples in the Denmark, Germany and indeed in the England of the seventeenth century?

It is curious to note the static conception of the world that these questions implied, though that may have been a necessary stage in sorting out the new knowledge which was then beginning to grow rapidly.

There seems to have been no thought that climate, and, for that matter, the racial mixture and biological inheritance of nations, could change in the course of the centuries.

Or is it possible that the leading men of affairs, and perhaps some of the scientists, in London, Paris, Florence and particularly in Zurich and Copenhagen were after all aware of the growth of the Alpine glaciers which were then threatening the villages and swallowing up the pastures about Chamonix and Grindelwald, while the same was happening to farmland in Norway and the ice was increasing on the seas about Iceland?

Certainly, Andrew Fletcher of Saltoun in Midlothian knew very well the disastrous run of years of failed harvests, famine and death that had overtaken the upland parishes of Scotland when he presented his Second Discourse to the Scottish Parliament in 1698 and criticized the well-to-do and comfortable population of the eastern lowlands for their lack of concern.

In 1492 the pope of the day had written of his concern for the people in Greenland because of the extensive freezing of the seas.

As is well known, the old Viking population in Greenland, cut off from Europe, ultimately died out or disappeared.

In 1784, in the time of a renewed increase of the sea ice around Iceland and after a massive volcanic eruption in that country, the Danish government debated whether Iceland should be evacuated and the population resettled in Europe — an amazing proposal in relation to the resources available at that date.

In the event, it was not attempted and ultimately proved unnecessary despite the immediate distress and loss of life.

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Post by thelivyjr »



The view, so widely held until recently, of climate as constant was perhaps no more than a premature conclusion from the first long records of weather observations made with standard meteorological instruments in the world’s leading cities.

Many of these records had covered a hundred years by about the end of the nineteenth century, and it so happened that between 1875 and 1895 the temperatures prevailing in Europe and eastern North America had reverted to values quite similar to those of just a century earlier.

In between there had been some colder decades with important glacier advances — a major climax of the glaciers in the Alps about 1820–50 — followed by a warmer time, which was in fact the beginning of a general recession of the glaciers all over the world until around 1960 or even later.

The conclusion that climate is essentially constant, which at first seemed to be the verdict of scientific observation, though in fact the hundred-year record was not enough to establish it, was at odds with the acquired wisdom and experience of previous generations.

It had actually been concern about ‘the sudden variations in the behaviour of the seasons’ to which the climate seemed ‘more and more subject’, and about possible effects on agricultural production and human health, that had led to the setting up of some of the first nation-wide networks of meteorological observations from 1775 onwards.

The assumption of constancy was, however, a convenient one for those practical operations using climatic statistics for planning.

It implied that the average values and general ranges of temperature, rainfall, sunshine, etc., indicated by the meteorological observations of ‘enough’ years (say twenty or thirty years) should serve as a sound guide to the future.

And no questions needed to be asked about which years the observations covered.

It even meant that valuable statistical techniques could be developed to derive estimates of the ultimate extremes of temperature etc. and the average recurrence intervals (known as the ‘return periods’) of rare events, using the frequency distribution shown by all the observed values of this or that element of the climate during whatever sample period was available.

Thus, construction engineers could be supplied with figures for the strongest gust of wind, the greatest flood or frost or the highest temperatures to be expected once in fifty, or even once in five hundred, years — all on the basis of a mere thirty years or so of observations.

The only important criterion seemed to be that the instruments, and their exposure, and maintenance of the observation record, conformed to the prescribed standards of the scientific age.

Climatology became essentially the book-keeping branch of meteorology — no more and no less.

A step in the direction of standardization was taken at the 1935 conference of the International Meteorological Organization (forerunner of the present World Meteorological Organization) when use of the observations of the years 1901–30 for all climatic purposes was recommended as the so-called ‘climatic normal period’.

Choice of the word ‘normal’ turned out to be unfortunate, but it has persisted in climatological practice.

It spreads the impression that nature recognizes such a norm and that conditions should continually return to the regime of the chosen period.

We now know that 1901–30 was a highly abnormal period, though it was surpassed by the following thirty years 1931–60, which were in due course substituted as the ‘new normal period’.

Globally, these were probably the warmest, and in many regions the moistest, periods of such length for centuries past!

The indications of climatic probabilities for future planning, particularly the occurrence of extremes and rare events, arrived at on this basis, have sometimes proved seriously misleading since about 1950.

It is certainly unwise to specify return periods of supposedly rare events much longer than the length of the observation record which has been examined.

This confronts us with the need to extend knowledge of the past record of climate beyond the era for which instrument observations are available.

The quest entails the use of various kinds of earlier documentary records and of ‘proxy’ data to which we will return in the next chapters.

The adoption ‘for practical purposes’ of a constant climate seems to have continued longer than it might have done for an understandable reason.

It worked.

But it has not worked so well in recent years.

In fact, from about the beginning of this century up to 1940 a substantial climatic change was in progress, but it was in a direction which tended to make life easier and to reduce stresses for most activities and most people in most parts of the world.

Average temperatures were rising, though without too many hot extremes, and they were rising most of all in the Arctic where the sea ice was receding.

Europe enjoyed several decades of near-immunity from severe winters, and the variability of temperature from year to year was reduced.

More rainfall was reaching the dry places in the interiors of the great continents (except in the Americas where the lee effect, or ‘rain-shadow’, of the Rocky Mountains and the Andes became more marked as the prevalence of westerly winds in middle latitudes increased).

And the monsoons became more regular in India and west Africa.

Planning on the climatic statistics of the preceding decades was in fact allowing wider safety margins for many activities than was apparent up to some time about 1950.

The almost four-and-a-half decades of near-immunity to very cold winters ended abruptly with Europe’s notably severe war winters in 1940, 1941 and 1942 and another in 1947 which is still remembered for its great snowfalls and very low temperatures.

Other cold winters followed in 1956 and most notably in 1963, which was a very long winter in many parts of the northern hemisphere and in England the coldest for over 200 years, since 1740.

And later in the 1960s the Arctic sea ice returned to trouble the coasts of Iceland.

There was another run of mild winters in both Europe and North America in the early to mid-1970s, but more European cold winters followed in 1979, 1982 and 1985, some of which affected North America also.

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Post by thelivyjr »


Not surprisingly, research into the longer-term behaviour of climate languished as long as things were satisfactory.

The lead towards a more lively view of climatology as the science of the development of climate had, in fact, been given by the Swedish meteorologist Tor Bergeron in 1930,1 but three decades were to pass before it was taken up.

Since about 1950 the climatic tendencies have changed.

A global cooling, slight at first but very marked in the 1960s in the northern hemisphere, reversed the earlier upward trend of temperature.

Obviously, a run of five or six mild winters in Europe after 1970, and three or four in eastern North America about the same time, plus two very warm summers in the same regions in 1975 and 1976, caused judgement to hesitate and produced an impression that the spate of writing in the 1960s about climatic change had overstressed the subject.

That was before the winters of record severity in parts of North America and Europe in the later 1970s.

But planners concluded that the political uncertainties surrounding the supply of basic fuels had to be seen as a greater threat to the economy.

There have, however, been very notable extreme seasons, famines and harvest shortfalls in various countries since 1960–70.

And these have been not unconnected with the political difficulties of the immediately following years.

This applies most obviously to the many years of drought in the Sahel and elsewhere in latitudes 10–20 °N and the 1973 revolution in Ethiopia which led on to international conflicts in the Horn of Africa.

It has even been suggested that it was the world grain shortage following the droughts and harvest failures in 1972 that triggered the first great oil price rise in the following year, as the oil-rich desert nations sought to secure their ability to buy food.

At all events, within a year the world price of wheat had doubled and that of oil had multiplied by four.

This is just one instance of how we find climate and its variability involved in the major problems of the present-day world.

But it is, of course, the great growth of the population, plus the demand for an ever-rising standard of living everywhere, which are straining resources, particularly as regards food production and water supply — in some years already demanding more than nature (aided by human technology) can give.

These experiences have created a demand for climate forecasting at a time when scientific knowledge is inadequate to meet it satisfactorily.

Until the 1960s improvements in agricultural technology, particularly the spread of harvesting machinery, aided by a run of some decades of benign climate, were reducing crop losses.

At the same time, increasing use of fertilizer and pesticides and the development of new seed varieties were greatly increasing yields.

Since then, however, demand has in most years outstripped production, so that by 1975 world grain reserves counted in days supply had fallen to less than a quarter of what they were in 1961.

In at least five years between 1960 and 1979 droughts affecting the harvests in the Soviet Union and sometimes in China as well, and failures of the monsoon in India, drove those countries to make massive purchases of grain from the west, essentially from the North American surplus.

In 1972 harvest shortfalls in all these areas together coincided also with the prolonged drought and starvation in the Sahel zone of Africa.

The burgeoning of the worlds population and the expectations of higher living standards clearly increase our vulnerability to climate fluctuations.

Vulnerability may also be increasing as a result of the rationalization of agriculture and world trade, whereby huge areas concentrate on just one or two crops which supposedly grow best there.

This in essence depends on a forecast constancy of climate; and when even in an individual year the weather conditions go beyond the expected range, the consequences may be drastic.

The one-crop economy was at the root of many of the greatest famines of the past.

In recent years, moreover, climates all over the world have shown once more an increased range of variability.

Adding to these problems, forward calculations of world population growth and energy demand have led to widely publicized forecasts of a drastic rise of the global temperature, leading to displacement of the agricultural belts.

This is seen as an inescapable effect of the extra carbon dioxide introduced into the atmosphere by our burning of fossil fuels (coal and oil, etc.), as well as strange substances, including nitrogen oxides from our artificial fertilizers, and the waste heat from these and other processes (e.g. nuclear energy).

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Post by thelivyjr »


Estimates published of the warming to be expected by the year 2100 range from 2 to 11°C, the more extreme ones implying that the level of the world’s oceans should begin to rise rapidly as melting of the land-based icesheets in Greenland and Antarctica got under way.

This is an opinion, seemingly founded on firm scientific knowledge, which has to be taken seriously, even though we may notice some grounds for doubt and scepticism.

It was against this background that Dr Henry Kissinger, who was at the time United States Secretary of State, in a speech at the United Nations General Assembly on 15 April 1974, mentioned the threat of climatic changes and pressed the appropriate international scientific organizations ‘urgently to investigate this problem’.

The World Meteorological Organization has for some years been organizing a Global Atmospheric Research Program (GARP) with the climate problem as one of its objectives.

The United States took the lead in adopting by Act of Congress in 1978 a National Climate Research Program and urging designation of the twenty-year period 1980–2000 as International Climate Decades, to secure broad international co-operation in the collection and analysis of all available climatic data and study of the problem.

In other countries there has been so far too much concentration on theoretical modelling, based on the observations made in just those recent years for which global coverage is available.

It is also necessary to have whatever observational data can be gathered to cover a much longer period of time, long enough to survey a statistically useful number of repeats of all those natural processes of climatic change and fluctuation which may be important to our future planning periods.

Sir Crispin Tickell, a former Fellow of the Harvard Center for International Affairs and British representative at the United Nations, has put very clearly the awesome implications of the growth of the human population of the Earth and of the climatic changes which we may engender.

In his Presidential Address to the Royal Geographical Society in 1991 he stated: 2

The surface of the planet…is changing fast…the impact of industrial society has caused human population to multiply out of control …it has to come down sooner or later…the population was 2 billion when I was born (1930) and is now 5.3 billion and will probably be about 8 billion by 2025.

And he went on:

the rough carrying capacity of the Earth for people enjoying Western dietary standards is about 2.5 billion….

In short, we are on a rollercoaster to disaster if we do not grasp what is happening….

We have to work for a new broad equilibrium involving changes in our energy policy.

He returned to the theme in his Presidential Address in 1993: 3

The prime engine of the dizzy-making rise in the human population and change generally is the industrial revolution.

We have the misfortune to be perhaps the first generation in which…the global price to be paid is becoming manifest.

There are many aspects….

The most significant change is not the spread of brick, stone, concrete and urban sprawl, but…the destruction of forests world-wide and declining fertility of soils….

Disposal of chemical wastes is a world-wide problem….

No part of the world is now exempt from the wastes produced by industrial activity.

Examples of population declines in the past, some of them catastrophic and clearly responsible for ending whole chapters of history in the regions affected, are mentioned in this book.

In some cases climatic events clearly played a part, commonly in connection with diseases and wars triggered by the stresses on human life and the economies on which the people depended.

Probably the best known cases are the great plague which spread all over the Roman world and beyond in the emperor Justinian’s reign, in AD 543–7, and that other great pestilence, known to us as the Black Death, which reached Europe from the Far East in 1348–9.

In both these cases, disturbances of the accustomed weather regime seem to have been involved in the origins of the outbreak.

Both occurred in times of intermittent great storminess and wet interspersed with some years of drought and great heat.

In the late Middle Ages, the disastrously wet summers and failed harvests in Europe between AD 1310 and 1320, worst in 1315, had been followed by a similar run of years with great rains and river floods in China in the 1330s, notably in 1332.

These conditions in the great river valleys and broad plains of China are believed to have destroyed the habitats of the rodents and therefore their ways of life, and set them roaming and scavenging in new areas.

It may be significant that the earliest origin of the pestilence is set in inner China in 1333.

Abandoned irrigation works and cultivation systems in Asia Minor and the Arab lands from earlier times, as well as the mute archaeological evidence of great buildings and cities ‘swallowed up’ by later forest growth in central America and southeast Asia, point to other cases of vanished populations and drastic events and changes of the landscape in which climate presumably played a part.

These surely underline that Tickell's warnings should be taken as realistic.

A population disaster that is now reasonably fully documented, in which climate played a key part, as the trigger which finally unleashed the calamity that had been prepared by several factors 4 working towards the same result, is provided by the terrible Irish potato famine in the 1840s.

The warm damp weather which fostered the potato blight in 1845 and some of the very next summers affected much of western and northern Europe and caused potato blight in many countries.

It was, moreover, a new disease for which no one was prepared by experience.

It came fortuitously in a ship-load of potatoes from Latin America to Belgium and was wafted to Ireland by easterly breezes in July and August 1845.

Other breezes spread it to other countries, as far as Scotland, Norway and Poland, though in some that summer was too cold for the disease to flourish.

In Belgium and Holland, however, over three-quarters of the potato crop was destroyed in that year.

What made its attack devastating in Ireland was the social situation there.

The Irish population had been growing fast, from about 6 1/2 million in 1820 to nearly 8 1/2 million by 1845, nearly double what it has been since, until the late twentieth century.

It was a largely rural population, living on tiny farm plots, mostly under 6 hectares and some as small as 1 hectare, following generations of dividing the inheritance.

On such plots there was only one crop that could fill their bellies, and that was the potato, particularly the cheap Lumper variety, which unhappily proved to be especially vulnerable to the disease.

The prevailing poverty was such that many families could not even afford salt to make the monotonous diet more palatable.

Enormous numbers died and mass emigration on crowded ships began.

Moreover, Ireland’s position on the edge of the Atlantic, where the southerly and southwesterly winds are warm and especially humid, meant that the disease recurred, to devastate the crop in several successive years, whereas in 1846 a much drier summer saved most countries farther east.

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Post by thelivyjr »


Reconstruction of the past record of climate is one of the most broadly interdisciplinary projects of research.

Just as weather and climate touch almost every aspect of our lives and environment, so evidence of their past record turns up in a vast variety of places.

Most branches of learning, from studies of the writings and inscriptions of Classical and pre-Classical antiquity to work with the isotopes of elements identified by nuclear physics, have something to contribute.

Much of this work is cheap by comparison with the operation of the great meteorological computer laboratories used by the theoreticians to explore the performance of the atmosphere and oceans as simulated by their models.

In reality, both types of research are needed and there must be continual collaboration and interplay between them.

Commonly, however, the research funds made available have been of the order of twenty to fifty times as much to the theoretical work as to construction and analysis of the actual past record of climate.

As in all science, observation of the phenomena to be explained is needed before theoretical understanding of them can be established.

This is now being increasingly recognized.

In one connection, the theoretical laboratories should obviously have most to contribute: in exploring how the behaviour of the climate may be altered in future by man’s possible inputs of pollution and heat which never occurred in nature.

Even so, the theoretical results will only be trustworthy in so far as (a) the assumed quantities are realistic and (b) the ability of the models to simulate the real world has been tested by application to various climatic regimes which are known to have occurred.

We clearly need to know and understand more about climate.

It will not be amiss to point out some traps for the unwary in approaching this subject.

We are all — professional scientists, clients seeking advice, and laymen alike — steeped in the practical experience and ways of thought of the age we live in.

As a result, people considering the problem of climate and its current development commonly start from the following presumptions:

1 The basic observation data—in order to establish the facts beyond doubt— must be from a well-established network of observers with high-quality instruments, their calibration satisfactorily maintained and their exposure conforming to recognized modern standards.

2 The best answers to questions demanding prediction must surely come from the laboratories with the finest computers and most advanced mathematical models.

3 One can surely leave out of account the ‘long, slow processes of climatic change’.

4 Any changes of the prevailing climatic regime observed today, or on timescales of significance to forward planning, must surely be attributable to man’s activities.

The first two of these suppositions are of course well-learnt lessons of the scientific age, having proved their value in many other connections.

But we shall see that in coming to grips with the climate problem, all four items are prejudgements which need further examination.

Let us consider them one by one.

1 From the time of invention of the basic meteorological instruments — barometer, thermometer and rain-gauge—in the seventeenth century, 5 and the gradual establishment of a network of observation points equipped with them, until around 1950, the climate was mostly changing in one direction, towards greater warmth.

Some climatic processes and evolutions are therefore of long duration.

The opposite change, which had introduced the colder conditions and swollen glaciers at the time of the beginning of the instrument record, obviously provides another case.

If we wish to understand that change, and other regimes that have occurred in post-glacial times, we must find ways of reconstructing situations that existed before meteorological instruments were known.

This may appear all the more necessary as the observed climatic trend over much of the world from about 1950 to the late 1970s at least has been a cooler tendency.

2 Computer models simulating climatic development may also be deficient for a variety of reasons, however skilled the mathematics used.

In order to obtain the complete global observation coverage needed, the performance of the atmosphere and oceans which the models simulate is bound to be that of a rather short span of years since 1950 and is sometimes that of just a few recent years of specially arranged international observation effort, for example under the GARP.

Items crucial to the development of climatic changes over periods covering a number of decades or longer, being not really known from beforehand, may well have been omitted.

The models’ ability to explain climates of earlier times needs to be tested.

Moreover, many of the complex interactions within the atmosphere and between atmosphere and ocean, which must be simulated, involve so many unknowns (exchange coefficients and so on) that altering any of them must alter others and can lead to a range of virtually arbitrary results.

This is particularly true of models which do not incorporate the changes in the ocean induced by events in the atmosphere and the reaction of the former upon the latter, or the changes of cloudiness induced and their reaction upon the atmosphere and oceans’ heat budget.

In this present state of the science, actuarial estimates of frequency and probability of various occurrences, relying closely on the past observation record, are probably more generally acceptable as a basis for planning than the specific forecasts of the theoretician.

But what past observation period shall we use?

The frequency of a long spell of frost in England such as to freeze the rivers was twice in over forty years from about 1900 to the 1930s; but in the nineteenth century it had been two to four times a decade and since 1940 it has again been once or twice a decade.

(The run of mild decades at the beginning of the century allowed the development in Britain of water supply and drainage pipe layouts in, or rather on, the outside walls of the nation’s houses, which ignored the risk of frost. The electrification of British railways, begun in the same decades, adopted the third rail system, which was to become notorious for failures in frost.)

Parallel changes affected the frequency of snowfalls sufficient to block many roads and halt work on the land.

And we shall come across similar changes in this and other parts of the world concerning droughts and flooding.

All these experiences affected planning and design in the periods concerned.

Thus, seemingly objective statistical work may produce a variety of verdicts which are actually arbitrary in that they depend on the choice of observation period.

So here we again encounter the need for greater scientific understanding.

We must seek to select a datum period for the statistics we use that is really similar in the physical development of climate to the present and future period which we are planning for.

In this the observational worker needs the help of the theoretician to understand the evolutions of atmospheric circulation and climate which he observes and to be sure that he identifies like sequences correctly.

Observation and theory must advance hand in hand.

3 The processes of climatic change may be long — as we have already seen, some of them certainly are — but they include some step-like, abrupt changes.

Thus, the level of Lake Victoria, which is fed by the equatorial rains over its catchment basin in east Africa, rose by more than 1 m within three months in 1961, beyond the entire range of the previous sixty years since the gauges were installed; and by the late 1970s it still had not reverted to its previous levels (fig. 1).

Other great lakes in eastern equatorial Africa rose at the same time.

It is now known that the lakes were higher in the 1870s and that their decline by the end of the century had also been rapid.

(The low stand of these equatorial lakes in the earlier part of this century roughly coincided with the period of most persistent development of the prevailing westerly winds of middle latitudes, and seems therefore to have been bound up with a global change in the wind circulation and transport of water vapour.)

An important question therefore concerns the rapidity of some climatic changes.

4 The objection to the notion that any changes of climate which may be observed nowadays, or in the nearer future, must be attributable to man is that it is unproven and, outside urban and industrial areas, it is probably untrue.

We shall have more to say on the questions involved in a later chapter.

Nevertheless, in view of the increasing variety and scale of human ‘insults’ to the environment, there is clearly no room for complacency and every need for precautionary calculations and watchfulness.

Before we can go further in presenting what is now known of the past record of climate, or understanding its behaviour today, it is necessary to consider in outline how climate develops and the patterns of day-to-day weather are produced.

Happily, when one investigates the working of the large-scale wind and ocean circulations, some encouragingly simple aspects are found.

And, at least, it is clear that we can consider the climate system as a single global entity.

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