The human response to change

What conclusions can be drawn from this summary description of the processes and hazards of climatic change? Perhaps the first is to underline the fragmentary nature of our knowledge and the immense difficulty of assigning causes to effects. We can say on the basis of mathematical models that if such and such a factor could be isolated the result would be such and such. But in real life no factor can be so isolated, and there are many factors in this complex system of which we know little and there are probably others of which we know nothing.

Yet the second conclusion is surely that the attempt must be made. We have already greatly changed the environment of the earth, and every day that passes we change it more. Our actions are usually undertaken with local and short-term intent. Trees are felled, factories are built, cities spread out and up, heat is generated, to meet the particular needs of particular people at a particular moment.

By these means human society has grown in size and accomplishments like the accumulation of a coral reef around some tropical island. The builders of the reef worked to no plan and were largely unaware of each other's existence. So slow was the process that no one knew that they were changing the life of the shore, if not the island itself, by their actions. Yet the size and complexity of the structure, and the proliferation of creatures who came to live there could eventually threaten the conditions which first allowed its growth, and the ever-changing sea could always strand or destroy it.

We are more than coral reef builders or inhabitants. But the cumulative effects of our actions are so great that we too could damage the condition of our continued growth. To some extent we have the power to control and direct it. But we have to know what we are doing, and of course we also could be stranded or destroyed by changes in conditions from without.

The biggest threat we face is our own success as a species. Unlike most other animals we have contrived to remove most of the checks and balances which in the past kept us in our natural place. We have learned how to live in virtually every climate; we have changed the face of the continents to meet our needs; we face no serious challenge from other species, and know how to cope with most of the dangerous viruses and bacteria; we have changed the balance, number, and genetic inheritance of animals and plants for our own purposes; and we have a system of morality deriving from pack and tribal instincts which, in spite of habitual collective violence between human groups, has established a conscious community of mankind in which each has a certain sense of responsibility for all.

The result has been a vertiginous increase in human numbers, rising steeply from the beginning of the industrial revolution to an estimated 2,000 million in 1930 to around 4,100 million in 1975. The annual rate of increase in 1930 was about 1.1 percent. In 1975 it was around 1.8 percent, and is likely to stay at that level until the end of the century. By then there will probably be another 2,300 million people in the world. Of these, some 2,000 million will be in the countries least able to sustain them.

Birth rates may fall, even in poor countries, but death rates will fall with them. Short of disaster on a major scale, it is hard to see world population achieving stability until well into the next century and then at a level which many now would think an intolerable burden on the carrying capacity of the environment.

Many attempts have been made to look into the future. With so many imponderables it is probably vain to peer further than the end of the century, and even that is obscure. But certain predictions can reasonably be made:

• Under the pressure of population increase, particularly in poor countries, we shall see more extensive exploitation of land, and continuing migration from the country to the towns.
• Food production will increase, largely through greater efficiency in already favoured areas.
• Fisheries will also increase but there are limits to the food resources of the sea, which will require careful management.
• The world's stock of forests will continue to diminish, and loss of wood for fuel in poor countries will increase demands for other fuels.
• Demand for fresh water for irrigation, human consumption, and industry will double or even triple.
• Urbanisation and industrialisation will continue at exponential rates, and with them demand for energy.
• In broad terms, the gap between living standards in industrial and other countries will widen.

The impact on the environment could be severe:

• In agriculture there is likely to be more soil erosion, loss of nutrients, and more dust.
• Land will be surrendered to urban and industrial growth and irrigated land will suffer salinisation.
• Pollution due to increased use of pesticides and fertilisers and of industrial wastes is likely to increase: this is liable to extend to coastal waters with effects on fisheries.
• Fresh water will be in shortening supply with lowering of water tables and depletion of fossil water.
• Deforestation will lead to soil erosion and, as we have seen, the deserts will creep forward.
• The atmosphere will be further polluted with nitrogen and sulphur compounds and chlorofluorocarbons as well as increasing carbon dioxide.
• Not least there will be species extinction on a scale unknown in recent history, which could lead to serious loss of the world's reservoir of genetic variability.
• Most significant in political and economic terms will be the deterioration of conditions in countries and regions already living up to the limits of their resources.

Even on the best assumptions the world of the future will be still less of a natural forest of life, in which our species is an animal like any other, than an enclosure, cultivated for strictly human purposes, whose health depends for good or ill on conscious management.

The dilemma was well put by A. V. Hill:

"Some might [take] the purely biological view that if men will breed like rabbits they must be allowed to die like rabbits. . . most people will say No. But suppose it were certain now that the pressure of increasing population, uncontrolled by disease, would lead not only to widespread exhaustion of the soil and of other capital resources but also to continuing and increasing international tension and disorder, making it hard for civilization to continue: Would the majority of humane and reasonable people then change their minds? If ethical principles deny our right to do evil in order that good may come, are we justified in doing good when the foreseeable consequence is evil?" [12]

For the moment the notion of expansion is deeply embedded in our psychology. No country is immune from it. We look to meet increasing demands for food or higher living standards, and to rectify the lopsidedness of our present distribution of human wealth, by ever greater and more effective exploitation of natural resources, euphemistically described as development. Failure to develop or otherwise expand our economies has come to imply and perhaps to mean stagnation, dislocation, or even social breakdown.

No responsible and, still less, elected government could lightly sacrifice a short-term and direct advantage in terms of wealth and employment for its people to avoid a long-term, indirect, and uncertain disadvantage for the human race or life as a whole. Even the idea that we could dangerously pollute our environment has been described as a luxury of the rich; and even in so rich a society as the United States, it may seem more important to save jobs than to risk depletion of the ozone layer.

In few, if any, projections of the future is there any provision for climatic change. Whether significant change is likely in the tiny time-scale in which we can usefully look ahead is a matter of opinion. The central hazard in an increasingly crowded world is rather the certainty of climatic variability. As we have seen, the climate is fluctuating all the time and very small changes can have big effects.

In the past people have responded to change like any other animal. They have exploited the opportunities it provided; or they have moved elsewhere; or they have adapted themselves and made the best of it. Thus during the last glaciation, men were able to move across the land bridge which is now the Bering Straits to spread across the Americas in perhaps the greatest of population explosions before our own time. Desert droughts in the Sahara pushed populations southwards, or led to special adaptations like those of the Bedouin or of the Bushmen of the Kalahari. Warmer conditions in Greenland attracted farmers in the 11th century but they were gone by the 15th century when the cold returned.

By contrast, people can no longer respond to natural disaster by going somewhere else. Nowhere in the world are there any open frontiers left. Obviously some people are at much greater risk than others, especially those inhabiting the marginal areas between climatic zones (polar, temperate, desert, and tropical) and those dependent on a particular weather pattern such as the monsoon.

People can and will adapt to new circumstances; but they need time, new skills, and living space. The current decline in flexibility of response implies a new vulnerability to climatic change from any quarter, whether from outside the earth, from the processes at work within it, from the activities of mankind, or from all three.

In these circumstances it is worth looking at some of the possible consequences of climatic change. Both the range of possibilities and the time-scale in which change could take place are vast. But we should be wrong to think that movement to one or the other end of the range (assuming we are somewhere in the middle) would necessarily take a long time. Both drastic cooling and drastic warming could take place relatively quickly.

To judge from our inevitably fragmentary knowledge of what happened 90,000 years ago, glaciation could begin in even less than a century, and warming could begin even faster. In any case, much less than drastic change could, as we have seen, affect millions of people in one season, let alone a year or tens of years.

For some time most observers ready to chance an opinion have predicted a cooling trend, and as we have seen the world could face renewed glaciation around 4,000 years from now if other factors did not intervene. [13] The future combination of the earth's orbit, tilt, and wobble suggest a repetition of the events of the last ice age in terms of a 100,000-year cycle, beginning with warm conditions similar to, or warmer than, our own. Such warm conditions, abnormal in the sense that they have prevailed for only 10 percent of the last million years, have each lasted around 10,000 to 12,000 years. On this reckoning our time is running out. Cooling and warming can sometimes be abrupt. There may be such triggers as oscillation within the oceans, or sudden increases in volcanic dust.

The precise effects of cooling, fast or slow, are unknown, but we can make some guesses from what happened on previous occasions. The events of the Little Ice Age from roughly 1560 to 1850 A.D., with warmer and colder patches, are a matter of historical record. In Western Europe, colder winters and poor summers caused shorter growing seasons, occasional famines, and disruption generally, particularly in the acute period of the 1690s. The advance of the Alpine glaciers, crushing mountain villages in their way, is a little illustration of what would happen in the event of a major new glaciation. The present boundaries between climatic zones would shift southwards in the northern hemisphere and northwards in the southern one.

Each year the cover of snow and ice on land in the northern hemisphere would last longer or not melt at all. Growing seasons would become shorter, and yields from most of the present grain-growing areas of the world would sharply decline. It was once supposed that in such conditions there would be greater rainfall in the tropics, but this is not necessarily the case. Indeed, drought might come to areas now relatively free of it. The absorption of vast quantities of water into the spreading ice caps would lower sea-levels worldwide, exposing much of the present continental shelves and changing the pattern of evaporation and the directi6n of some winds and currents.

Obviously, the redevelopment of a glacier in the English Channel, the evolution of tundra conditions in the Great Plains, or the disappearance of New Zealand under ice would depend on particular temperatures and the extent of glaciation around the poles. But if anything like the last glaciation took place, we could say that most of Northern Europe north of the line of the English Channel, a substantial part of North America and the Soviet Union, most of the mountain countries of the world, and parts of China and Australia would be buried under ice hundreds, if not thousands, of feet thick.

The pattern would not be consistent. In some areas there might be little change. Differences in temperature and precipitation between one zone and another would be greater than they are now. Ocean temperatures in the tropics might even be warmer. But the world as we know it would have become unrecognisable, and its carrying capacity for life, including that of man, would be drastically altered.

But what now of movement the other way towards a warmer earth? In a perspective of millions of years a climate considerably warmer than the present is normal. It may be that we are now emerging from the cyclical glaciations of every 150 million years or so, as the solar system moves out of an area of galactic dust or the sun itself behaves in different fashion.

Whether these extraterrestrial influences will bring back the apparently warm and steady conditions of earlier epochs is highly speculative. But there are other factors of much shorter time-scale to suggest warming up. These are the work of our own species. We have already seen the changes made to the surface of the earth, the increase in energy generated or captured there, the development of heat domes over cities, and the injection of increasing quantities of carbon dioxide and other gases into the atmosphere.

Of most significance for the future is the increase in these so-called greenhouse gases. For any who doubt it, the state of the atmosphere of the planet Venus at 450ºC represents an awful warning.

During the last ten years an enormous amount of work has been done on the greenhouse gases. Although there are still a few voices in dissent, most concerned are convinced that warming will take place. In 1979 a panel chaired by Jule Charney concluded that if the quantity of carbon dioxide in the atmosphere should double (in other words, reach around 580 ppm) there would be a global warming of around 3ºC with a margin of error of 1.5ºC either way.

"... We have tried but have been unable to find any overlooked or underestimated physical effects which could reduce the currently estimated global warmings due to a doubling of atmospheric C02 to negligible proportions or reverse them altogether ... It appears that the warming will eventually occur... " [14]

These conclusions were examined and confirmed by another panel under the chairmanship of Joseph Smagorinsky in 1982. This panel also found that warming would be 2 - 3 times as great over the polar regions as over the tropics, and that warming would be significantly greater over the Arctic than over the Antarctic. Further inferences from use of models were that there would be increased run-off from polar and surrounding regions; snow would melt earlier every year and fall later; the moisture of soil in the summer would diminish in middle and high latitudes of the northern hemisphere; and the coverage and thickness of sea ice over the Arctic Ocean and around the Antarctic continent would decrease. [15]

These conclusions have not since been challenged. Of course they do not take account of any contrary natural tendency towards cooling. Nor do they reckon with the effects of other trace gases which might increase warming. The regional effects cannot yet be judged except in the broadest terms. But we can already say with Smagorinsky, that the warming would have more drastic effects in high latitudes than in low ones; that patterns of ocean current, wind, and precipitation would change; that sea-levels would rise if parts of the Arctic and Antarctic ice caps melted; and that the distribution and behaviour of living organisms, from plants to animals, would be affected. In short, the world would be a different place.

The timing is critical. Are any of these changes possible within the span of a human life? The answer is probably yes. The rate of increase in the greenhouse gases is related to the use of fossil fuels, the destruction of forests, and industrialisation generally. If the annual increase of 4 percent in fossil-fuel consumption in the 1970s had continued, atmospheric carbon dioxide might, other things being equal, have reached 580 ppm by the year 2030.

The rate has since dropped, and the date may have receded. But the trend is still the same way, and in any case perceptible warming could of course begin much sooner. It is not yet possible to say whether it would come gradually or in jumps; but if the greenhouse hypothesis is correct, many people now alive will be there to witness its results.

In examining what might happen to them and later generations, it may be worth looking back into the past. The further back in time we look the less good the analogy can be, not only because of the increasing fuzziness of our information but also because some of the climatic determinants were probably different. Even so, conditions prevailing during three warmer periods in the past have some relation to what might happen in the future. [16]

The first such period was in the early Middle Ages, between 850 and 1250 A.D., when average temperature in low and temperate latitudes, with variations in time and place, was probably around 1ºC more than today. The effects were most evident in the frontier areas between climatic zones - the Arctic, the temperate, and the desert:

• The Arctic seems to have retreated towards the pole: in warmer and wetter conditions forests advanced, cereal production took place in Iceland, Norway, and even Greenland, and the disappearance of sea ice from the East Greenland current affected the migration of fish.
• Further south, summers were warmer and winters cooler with severe droughts in some areas, particularly Eastern Europe.
• Vines were cultivated some 3º to 5º further north than now and 100 to 200 meters higher above sea-level.
• The southern part of the Mediterranean was probably wetter, and more rain fell on the northern Sahara.
• In North America, there was a comparable pattern of change in the early part of the period: one result was the increasing desiccation of what is now Mexico and the south-western part of the United States.

Climatic variation could well have been a contributory factor to the expansion of the Norsemen in Europe and of the steppe peoples of Asia; it may earlier have helped precipitate the collapse of the classic civilisations of pre-Columbian Mexico.

The second period was between 5,000 and 7,000 years ago, when average temperature in low and temperate latitudes, again with variations in time and place, was probably around 1.5ºC more than today. This was the warmest period in world history since the end of the ice age. But melting of the ice sheets and glaciers following the end of the ice age was incomplete, particularly in North America. This created a marked asymmetry or meteorological distortion in atmospheric circulation between 8,000 and 6,500 years ago. Mankind had not yet begun the clearance of forests and vegetation which later contributed to the process of desiccation and extension of desert conditions.

Subject to these qualifications, the pattern seems to have been similar to that of early mediaeval times but more humid. [17] Although the forests advanced northwards and upwards, conditions in the subarctic were, with the exception of Alaska, warmer and drier than they are now. But Western Europe, parts of the Mediterranean, and even the Near East were wetter, and parts of the Sahara formed a luxuriant prairie.

India, eastern China, East Africa, and western Australia were likewise wetter, and parts of the Antarctic could have been warmer. Less is known about conditions in the Americas, but it seems that Mexico and what are now the prairie lands of the United States were drier. Towards the end of the period, water from the melting ice combined with changes in land released from the ice burden raised sea-levels with drastic effects on shorelines.

The third period was around 125,000 years ago, in the warmest patch before the onset of the last ice age which persisted with fluctuations from about 70,000 to 10,000 years ago. Present information suggests an average temperature in low and temperate latitudes of between 2ºC and 2.5ºC higher than now, with many regional variations and considerably more humidity. The land then looked very different, not least because the sea was 5-7 meters deeper.

But the broad pattern was not dissimilar, with a northward shift of climatic zones in the northern hemisphere. Southern England was then the home of the hippopotamus, the elephant, and the lion, and was covered with thick deciduous forest. Arctic sea ice was displaced towards the pole but the central core of Arctic sea ice, and the Arctic and Antarctic ice caps, were fundamentally the same, if smaller than they are now.

It is not worth looking back further. We simply do not know enough. But the record is at least a guide to speculation. Few serious attempts have been made to fill in the details of a world warmer by around 3ºC. The regional complexities are too great. The Climatic Research Unit of the University of East Anglia in Britain has tried the more modest approach of using cold and warm years earlier in this century to construct models which might reflect conditions in a northern hemisphere warmer by 0.5ºC.

Their most plausible model is based on the contrast between the 20 coldest and the twenty warmest years between 1901 and 1980. On this reckoning the Western European spring, summer, and autumn come out warmer, and winter cooler. Spring and summer are generally drier; autumn is wetter north of the Alps, and drier south of them; and winter is wetter south of the latitude of the English Channel, excluding the Mediterranean coast, and drier north of it, excluding Scandinavia. There is generally more variability of rainfall to the north and less to the south.

For most of North America there are warmer temperatures in all seasons with one or two cooler belts in the south. In the spring it is drier in the north and in Mexico, with a wet belt between them and up the Pacific and Atlantic coasts; in summer dry and wet areas move south and west; in autumn all but the coastal fringes are drier; and in winter the north, east, southeast, and west coast are wetter, with Mexico and the middle west drier. There is generally more variability of rainfall along the coast and less in the continental heartland. [18]

Even this tentative forecast, which shows similarities with the conditions which prevailed in early mediaeval times and around 6,000 years ago, carries big economic implications, in particular for agricultural production and energy consumption. If global warming were to continue upwards, both the resulting changes and their economic implications would become greater and less predictable. The land itself would assume a different shape. Even a small increase in world sea-levels would affect shorelines and harbours.

At present, sea-levels are slowly rising at the rate of 10-20 centimetres per century. An increase in global temperatures to yield an average of 3ºC would have most effect at the poles, and there would be substantial melting of polar and glacial ice. The rise in sea-level has been calculated at around 70 centimetres during the next 100 years. [19] But this might only be a beginning.

The grounded ice sheet in West Antarctica has long been suspected of instability, and as we have seen could have disintegrated in the past, as around 125,000 years ago when the sea was 5-7 metres deeper. It cannot be excluded that it might do so again. If this were followed by melting of other parts of the Antarctic and Arctic ice caps, sea-levels could rise so high that most of the world's great cities and much of its agricultural land would disappear beneath the water (see Figure 7).

Figure 7: The rise of world sea level as the former ice-sheets melted and through post-glacial times. The dates are corrected radiocarbon dates. The figure shows three reconstructions:

1. a very smooth mathematical 'best fit' curve, eschewing all detail;
2. a highly regarded reconstruction of the main stages, calculated from numerous dated shorelines in the Baltic after subtracting the steady rise of the region as the landrecovered from the former ice-load;
3. a carefuly calculated more detailed curve, due to Mörner, supported by points of agreement between reconstructions in different regions.

Courtesy of H. H. Lamb and Methuen Ltd.

On the land there would be a shift polewards and upwards of temperate conditions. So far as agriculture is concerned, there would be longer growing seasons in higher latitudes, and the areas best suited for grain production would move to the north. The higher concentration of carbon dioxide in the atmosphere would probably favour photosynthesis and increased production, and some plants in dry areas might flourish on less water.

The balance of advantage and disadvantage would be local or regional. But it seems likely that production in the main existing grain-growing areas in the world, particularly in the United States and the Soviet Union, would on balance be adversely affected. In all cases it would take considerable time, effort, and investment to adjust to new circumstances, even in areas where they were broadly favourable. Any change would cause disruption in the short term.

This would also be true of animals, each with its own place on the food chain and with its ecosystem. For example, insects usually increase in numbers and species with higher temperatures. We might therefore face a greater, or at least a different, problem in seeking to control pests. Changes in the pattern of wind and ocean current would affect the supply of nutrients and thus the location of the world's fish.

How other animals, including domestic ones, would adapt would depend on how mankind was able to cope with the myriad problems which would arise for each country and for society as a whole. We should also have to reckon with a further range of specific man-made problems. For example, as cities increased in size to accommodate rising population and more energy were generated in or around them to meet human and industrial needs, the extent and temperature of current heat domes would increase. All these problems go further and wider than climatic change, but climatic change could be of critical importance in dealing with them.

So much for the two extremes, cold and warm, each on its own time-scale, neither of them less plausible nor less likely for being extreme. They help us to realise how much we are creatures of our present balance between them, and how disrupting a major tilt in either direction would be. Each hypothesis tends to leave out the factors which support the other, and their synthesis remains out of reach of human calculation.

The further we look, the more we find missing from our equations; and even if we fully understood the natural rhythms of climatic variability, we would still be unable to predict the future from the past. For the activities of our own species have in this, as in so many other fields, produced new factors which make the past an uncertain guide.

More specifically, we cannot now exclude the thought that natural and man-made trends are already at war with each other. Even if our acts are at present inadvertent, a time may come when we may wish to proceed more deliberately. We might even wish to construct a kind of international thermostat for the management of the world's climate. We may be sure that it would be designed to maintain the status quo.

For most people the best that can be done is to work in the hope and on the assumption that something like the present climate will continue indefinitely. Drastic cooling or drastic warming look like science fiction, and even fluctuations, being unpredictable, have been excluded from individual, national, or international planning. In the memories of the majority the climate has not changed often or drastically enough to bring about worse than local or temporary disruption.

Thus, the swings of current climate, seasonal or otherwise, have come to be seen as the extremes of variability, and on that basis land and resources have been occupied, cultivated, and developed to the natural limit. For the minority along the boundaries between climatic zones the hazards have always been greater, and people have adapted themselves accordingly. But even their memories are short.

One of the reasons for the extent of the disaster in the Sahel since the early 1970s is that the nomadic inhabitants, encouraged by so-called experts from outside, had begun to settle down, and had increased not only their own numbers but those of their herds of cattle and goats far beyond the grazing capacity of the land in other than optimum circumstances. The effects of a periodic drought were thus multiplied into a natural as well as human catastrophe.

It may be understandable that climates should seem to last forever, but if this assumption did little harm in the past it could do a lot now or in the future. An assumption of stability invites planning for the optimum, and planning for the optimum leads to maximum exploitation of land and other resources. Any man-made system, whether a machine, a bridge, or a farm, tends towards the optimum, and the optimum tends to exclude the apparently unnecessary or redundant. Provided that stability is maintained, the system should work with increasing efficiency as improvements are constantly made to it.

The same goes for the adaptation of an animal species to its environment. But the moment the environment changes, those who are best adapted to it suffer most and have the greatest difficulty in adjusting themselves. Without tolerance in its working parts the machine cannot withstand shock; without some measure of engineering redundancy, the bridge collapses under stress; and without flexibility in land use and genetic variability in crops, the farm is ruined by prolonged rain or drought.

If excessive reliance on the optimum was the lesson of the Sahel, it could be the lesson elsewhere in the future as governments seek with all the apparatus of technology to produce greater and greater yields under the relentless pressure of increasing population.

This is not the occasion to reopen the controversy over the balance of population increase and food supply initiated by Malthus in his famous Essay on the Principle of Population in 1798. It is enough to say here that maximum exploitation of land and other resources for the production of food, can prove hazardous if not dangerous to present as well as future generations if it is based on the notion of a stable environment and ignores the climatic dimension.

The variability of the climate requires a corresponding variability in those who live in it, whether animal or plant; and all future planning, all development of skills for increasing food supplies and raising living standards, must take account of the possibility of drastic change and the certainty of continuing fluctuations, and thus be so far as possible geared to the worst rather than the best in prevailing circumstances.

The need for such an approach has been well illustrated by events since 1950. The first half of this century showed a steady warming trend virtually worldwide. Thereafter there has been a series of upsets of no clear pattern, except perhaps a tendency to short-lived extremes. [20] Records are of course better than before, and, although there are significant gaps in world coverage of meteorological events, we know far more about what is happening in other parts of the world. It may be worth giving a few examples:

• Between 1960 and 1969, central Chile suffered the driest decade since the end of the 18th century.
• 1962-65 was the driest 4-year period in the eastern United States since records began in 1738. In 1968 began the severest phase of the continuing drought in the Sahel zone of Africa.
• 1972 was a classically bad year: cold spread southward from the North Pole with record low temperatures reported in Greenland and the east Canadian Arctic; changes in the route of the circumpolar jet stream caused the worst heat and drought in the Moscow area for many centuries and excessive rain in the grain-growing areas of the United States and Canada; and along the boundaries of the tropics a swathe of droughts went round the world, affecting sub-Sahara Africa (including the Sahel), India and Southeast Asia, parts of China and Australia, and Central and South America (where El Nino took the Humboldt current out to sea).
• In 1973-74, floods beyond all previous recorded experience stretched across the central Australian desert. In 1975-76 came the great West European drought, and in 1978-79 the severest winter and lowest temperatures recorded in 200 years in parts of northern Europe and around Moscow.
• 1982-83 saw another visit of El Nino, this time with abnormal results which directly or indirectly affected climate in both hemispheres.

These extremes cannot be given a single origin or underlying cause. But certain features can be identified. Among them has been a greater frequency of blocking pressure systems in the Atlantic, causing a decline in westerly winds over Western Europe. There has been a marked cooling in the Arctic, bringing more Arctic sea ice to the coasts of Iceland for more than 50 years.

By contrast there has been a mild warming in the Antarctic and the sub-Antarctic areas, and a general increase of around 1ºC in average temperatures in New Zealand. In broad terms, spring has come slightly later to England, and autumn frosts slightly earlier to the Canadian prairies. In the 1970s, glaciers in Europe and North America began a modest advance.

What should we judge now or in the future as significant? Perhaps the three most interesting points to watch are temperature and precipitation at the poles, especially along the seasonal ice boundaries; wind circulation and blocking in temperate latitudes; and temperature and precipitation on each side of the equator.

During these 30 years or more of freakish weather, world food production has shown a fairly steady increase. This was substantially the result of the application of new ideas and technology to agriculture, from new irrigation schemes to the introduction of miracle grains. But even if production increased year by year (with a few exceptions) and the world distribution system improved, the differences between countries and regions became greater.

In some parts of Africa, food production actually declined; elsewhere it scarcely kept pace with the demands of rising population; only in a few largely temperate countries possessed of fertile soils and advancing technology was there the steep increase in productivity which raised world averages.

Since the 1930s, the pattern of the world grain trade has undergone particular change. Once Western Europe was the only substantial importer of grain. Other parts of the world were self-sufficient or net exporters. But by the 1970s the only major exporters left were the United States and Canada (with Australia, Argentina, and New Zealand far behind). The other main regions - Asia, Africa, the Soviet Union, Eastern Europe, Western Europe, and Latin America - had become net importers.

It should be added that within this pattern much of North American grain exports to Western Europe are now animal feeds, a token of higher living standards in countries whose production of other agricultural commodities is in embarrassing surplus. Elsewhere, particularly in poor countries, the import of North American grains in bad years has become a factor of importance in keeping growing populations alive.

The steep rise in oil prices in 1974 and 1979 served to bring out another vital point. They revealed how dependent food production, in particular that for miracle grains, was upon the supply of nitrogen fertiliser. Natural gas is a major element in its manufacture, and energy a major cost. The areas where the use of fertiliser would have the best result (in short, those areas where it has so far been relatively little used) are those which could least afford higher prices. The same goes for many pesticides.

By the beginning of the 1980s, it was clear to those who wished to see how precarious food supplies for a world population increasing by 1.8 percent a year had become. There have been many brave words about what modern technology can do in the cultivation of the global garden. But as we have already seen the prospects are scarcely cheerful.

There is increasing world dependence on one major grain-growing area to supply deficits; the possibilities for a significant increase in the quantity of land under cultivation, particularly in poorly endowed countries, are uncertain: the problem is rather how to improve or even sustain the productivity of existing land; the success of new agricultural methods, including miracle grains, has its limitations and dangers; fresh water is already in short supply for agriculture as well as industrial and other purposes; and even the sea - the source of life itself - is not a bottomless resource.

In such circumstances every small fluctuation in a continuously fluctuating climate can present a progressively greater challenge. There is an increasing risk of social disruption within regions, countries, and communities over such age-old issues as fertile land and water supplies, of deepening division between rich and poor in favoured and unflavoured parts of the world, and, perhaps worst for our species as a whole, of fouling the future for the sake of the present.

For, as we have seen, the climate itself could be put at risk by the activities, deliberate or inadvertent, of mankind, and governments will be tempted, under pressure from the hungry, the deprived, or the unemployed, to take actions which not only beggar their neighbours, but also damage or alter the delicate mechanisms of the atmosphere.

None of these horrendous things may happen. We may achieve a balance in our affairs and a limit to our population with no more than local disruptions and disasters to which we are - or should be - accustomed. In any case there is much that we could do if we had the will to do it. The remainder of this book is devoted to consideration of what is being done and what could be done within the climatic dimension.