A perspective on Climate Change free of the shouting, manipulating, and politicising – from 1983

Time-Life Atmosphere

Before the internet was born – in 1983 – Time-Life Books Published a series on Planet Earth. One of those books was titled Atmosphere and was edited by Oliver E. Allen. Chapter 6 was titled, ‘Prophecies Of Climates To Come’.

You can read it below. It brings perspective and allows you to draw your own conclusions. So I will do the same.

‘During the 1970s a succession of unexpected and almost freakish weather events afflicted various parts of the globe. Bitter cold spread southward from the North Pole, and Arctic pack ice began drifting into temperate latitudes, posing a threat to shipping. Portions of the Soviet Union experienced their worst drought in centuries, while U.S. and Canadian grain growing areas were beset by ruinously heavy spring rains. Year after year of extraordinarily scant rainfall in India and in the sub-Saharan region called the Sahel caused famines that claimed more than 200,000 lives. The winters of 1976-1977 and 1977-1978 brought murderous cold and snow to the Eastern United States. Snow fell in Miami, and in March 1978, Boston endured a “snow hurricane,” an unusual blizzard with 100-mile-an-hour winds that dumped 27 inches of snow on the city in 24 hours. In 1979 all of the Great Lakes froze from shore to shore for the first time in memory. A European Common Market commission, announcing a major study of climate trends, pointed out that, during the previous 15 years, Europe had suffered the coldest winter since 1740, the driest winter since 1743 and the severest drought since 1726-but also the mildest winter since 1834 and the hottest month in 300 years.

With records tumbling everywhere, it seemed to many that something odd and perhaps drastic was happening to the world’s weather. There were suggestions that a trend toward prolonged global cooling – perhaps even toward a new ice age – had begun; but others thought the trend was in the opposite direction, toward rising temperatures worldwide. Any such change would be of far more than academic significance. Even slight fluctuations in average temperature can affect the length of the growing season and, consequently, agricultural yields. Long-term variations in temperature also mean new patterns of energy use for heating and cooling. Since both food and fuel are potential sources of conflict among and within nations, making proper allowances for the role of climate in human events can be of critical importance.

With the aid of a stereomicroscope, William J. Robinson of the University of Arizona reads an ancient climatic record chronicled in tree rings.
The thin rings (between arrows) in a section of a Douglas fir were caused by a drought that lasted from 1276 to 1299 A.D.

Amid all the discussion of various alarming possibilities, climatologists – scientists who study long-term changes in weather patterns – remained notably circumspect in their interpretation of the wild fluctuations in the weather of the 1970s. For one thing, they had amassed enough data about past climate to know that erratic swings from drought to flood and from blizzard to heat wave have been common throughout the earth’s history. In fact, climatologists are generally in agreement that, after having enjoyed an unusually favourable period of few meteorological extremes for approximately 80 years, the earth is reverting to a more normal routine-such as that of the 1970s-in which natural excesses are likely to occur with unpleasant frequency.

During the era of benign weather that began around 1890, the world’s climate was both warmer and more stable than anything mankind had experienced for almost 1,000 years, giving rise to the widespread impression that climate does not change much. This impression was partly the result of a lack of information about the long-term trends of the past. It had not been possible to make accurate measurements of weather conditions until the 17th Century, when the necessary instruments were invented, and for decades thereafter record keeping was spotty.

A core sample taken from 300 feet beneath the Pacific Ocean floor near Mexico provides valuable information about the climate nearly 100,000 years ago. Each pair of light and dark bands represents one year of sedimentation: The light layers are the remains of microorganisms that flourished near the ocean surface during the dry season; the dark bands indicate silt that washed into the ocean from the land during the rainy season.

Nevertheless, modern climatologists have found ways to deduce the temperature and rainfall patterns of the distant past by studying historical records of such things as wine harvests, the annual blooming of cherry trees in Japan, and the growth and contraction of desert areas and alpine glaciers. In addition, they have measured the width of the annual growth rings of 5,000-year-old bristlecone pine trees, analyzed the chemical content of ice cores taken from the depths of the Greenland and Antarctic icecaps, pondered traces of pollen found in sedimentary rocks, examined the ancient remains of microscopic organisms in sea-floor sediments, and explored layers of silt and clay built up over the centuries on lake bottoms.

From such diverse data scientists have constructed a picture of repeated and extreme climatic fluctuation; in the past 700,000 years, there have been seven ice ages, interspersed with milder interglacial periods. The earth is now enjoying an interglacial that began some 11,000 years ago. During this period there have been a number of swings between moderate cold and warmth, some of them affecting different parts of the globe at different times. One warm spell, called the Big Climatic Optimum, peaked around 4000 B.C. and was followed by cooler millennia. The next warm period began about 500 B.C. and lasted more than 1,500 years (although a minor cold spell intervened from 700 to 800 A .D.). As the warming trend continued, Europe experienced the Little Climatic Optimum from about 800 to 1250 A.D.

This was the age of the Vikings, when Norsemen not only invaded northern Europe but expanded their territorial domain to encompass Iceland and Greenland; Leif Ericson and others are thought to have pressed even farther west to America. Greenland was named when its shores were indeed verdant, and the Norse settlers were able to raise oats, barley and rye. The colony grew until it comprised some 3,000 settlers living on 280 farms. The Little Climatic Optimum was so warm that vineyards flourished in England, producing wines that supposedly rivaled those of France.

Around 1250, the balmy days of the Little Climatic Optimum began slowly but surely to wane. England once again became inhospitable to wine grapes, and on the Continent, vineyards that had flourished on hilltops had to be moved to lower, more protected sites. Long stretches of wet weather introduced a protracted cool period, and the particularly sodden decade of 1310 to 1320 brought terrible suffering to England and northern Europe. In some years wheat harvests were so poor that farmers did not even have enough grain to use as seed the following year. As a consequence, the price of wheat tripled, and death from starvation and related diseases reduced the population of some parts of England by two thirds.

Meanwhile, ice floes began to clutter the waters around Iceland, hindering access to Greenland. Soon, ships were unable to reach the Greenland colonists, farming became impossible and the settlement withered. In 1492 the Pope expressed concern that no bishop had been able to reach his Greenland flock for 80 years; he did not know that the last of the settlers had died by 1450. When a Danish archeologist began excavating a Norse cemetery on the Greenland coast in 1921, he found macabre evidence of the intensifying cold. The oldest remains were buried several feet below the surface, but later graves were shallower; evidently, the permafrost zone had moved upward, making deep digging impossible with primitive tools. The most recent graves – about 500 years old – were very close to the surface, which by 1921 had itself been hardened by permafrost.

The cold that turned Greenland into a frigid wasteland afflicted parts of Europe in the 15th Century. Temperatures began a decline that was not dramatic – they were, on the average, only 1° to 2° F. below those of 1200 – but winters became longer and more severe, and summers were cooler and shorter. This climatic phase would last more than 300 years and would come to be known as the Little Ice Age.

With crops often damaged or destroyed by early-autumn frosts, food supplies were in some years inadequate, and famine again took a terrible toll. A vision of the era is seen in the work of the Flemish painter Pieter Bruegel the Elder, who portrayed cloudy, snow-clad landscapes filled with ice skaters plying the frozen canals and hunters making their way through the drifts. Ice floes drifted farther and farther south; sometime in the 14thCentury a polar bear stepped ashore from a floe that had reached the Faeroe Islands, just 250 miles northwest of Scotland. The Thames River froze six times as often during the Little Ice Age as it had during the Little Climatic Optimum. Henry VIII took advantage of one of these occasions in 1536 to travel on the ice by sleigh from London downriver to Greenwich. In the Alps the glaciers crept down the mountainsides, often crushing houses that had been built in warmer times. As late as the 18th Century, the Little Ice Age was still in full cry. At one point during the American Revolution, Britain’s fleet was immobilized by ice in New York Harbor; cannon could be slid across the harbor from Staten Island to Manhattan.

Londoners frolic on the icy surface of the Thames River in this 1677 painting by Abraham Hondius. The Thames froze an unprecedented 10 times during the 17th Century, at the height of the period called the Little Ice Age.

Asia was not spared the Little Ice Age. The cold settled over Japan and China in the 10th Century and lasted until the 14th Century, then moved westward to European Russia in the mid-14th Century and onward to central and western Europe in the 15th Century. Exactly why the large-scale climate shift traveled slowly around the globe in this manner rather than descending over the entire Northern Hemisphere at once remains a puzzle to climatologists.

Records from the Southern Hemisphere are sketchy, but it appears that, at times, the Antarctic pack ice actually receded as the Arctic’s was advancing. This has led to the suggestion that climate trends in the two hemispheres may be out of phase with each other, one warming while the other cools. The evidence is far from conclusive and, in fact, other research indicates that the hemispheres experience similar climate changes, with Southern Hemisphere trends leading the changes in the north by one or two thousand years.Very gradually, imperceptibly at first, the cold began to slacken; during the 19th Century, average temperatures increased a degree or two in the northern temperate latitudes. In the French Alpine village of Argentière, a glacier that had been pushing into the community’s streets stopped in the 1850s, and soon began to retreat. Growing seasons lengthened and the Arctic pack ice retreated. The trend toward more benign weather lasted until World War II. Perhaps by coincidence but perhaps not, this was the heyday of Western imperialism, in much the same way that the Little Climatic Optimum had seen the Norsemen flourish; worldwide population surged upward, its growth sustained by bountiful harvests.

Around the middle of the 20th Century, temperatures in the Northern Hemisphere once more began to inch downward. Between 1940 and 1965 the Northern Hemisphere cooled by about 0.5°F., on the average, and from 1951 to 1972 temperature in the North Atlantic declined steadily. In parts of the United States, the trend was even more pronounced; average temperatures dropped by 1° to 2°F. in summer and 4° to 5 °F. in winter. In 1974, climatologists George and Helena Kukla concluded a study of weather maps and satellite photographs of Arctic conditions during the previous seven years. They had discovered that the snow and pack-ice cover in the Northern Hemisphere had formed earlier, and had covered a larger area, in each of the last three years of the period than in the first four.

The Kuklas suggested that the meteorological extremes experienced in Europe and North America during the early 1970s might be linked to the increased snow cover. When the polar region grows colder in relation to the Equator, its cap of cold air tends to bulge farther southward than normal, developing more pronounced waves along its outer edge. These projecting lobes of cold air deflect the surface westerlies of the middle latitudes farther south, with consequences for climatic change that have been traced by a number of climatologists. Jerome Namias of the Scripps Institution of Oceanography proposed that the cold winters the United States had experienced during the 1970s could be attributed to a persistent, southward-projecting flow of cold polar air. Another scientist, ReidA. Bryson of the University of Wisconsin, argued that a similar kind of pattern was responsible for the devastating drought that struck Africa’s Sahel region during the late 1960s.

Even in good years, rainfall in the Sahel is barely adequate to support farming and livestock raising. The African monsoon, which normally sweeps in from the South Atlantic across the nations on the coast, brings desperately needed moisture to the thirsty Sahel sands, much as the Indian monsoon normally drenches the lands south of the Himalayas. But in the late 1960s and early 1970s the African monsoon rains failed to reach the Sahel several years in a row; during the same period, the Indian monsoon weakened, and crops suffered in China. The failure of the African monsoon occurred, according to Bryson, because the deflection of the westerlies southward over Africa had displaced a large anticyclone that is an important determinant of local climate. This dry, high-pressure system normally hovers above the Sahara. When the monsoon encounters the southern edge of the anticyclone, its moisture condenses and falls as rain over the Sahel. But when the anticyclone is displaced southward, as was the case in the late 1960s and the early 1970s, the monsoon drops its burden of moisture before it reaches the Sahel.

Climatologists generally agree with the link Bryson proposed between the course of the westerlies and the drought in the Sahel. According to Bryson, the same mechanism – polar cold prompting a prolonged southward deflection of the westerlies – can be invoked to explain climatic variations in the past, such as the changes that began to affect much of the Northern Hemisphere around 1250, when Greenland grew colder and the Norse settlement went into decline. The drought that gripped the North American plains east of the Rocky Mountains at the same time may also have been the result of the southward-deflected westerlies; remaining over the region, they may have prevented moisture-laden tropical air from moving northward.

But the westerlies, and even falling polar temperatures, are only intermediaries and not initiators of climatic change. What could cause the Pole to cool in the first place? Bryson suggested that the drought in the Sahel – and, indeed, the global cooling trend that has only recently reversed – may ultimately have been triggered by dust. He argued that small particles in the atmosphere, especially pollutants and volcanic ash, can block a good deal of incoming solar energy while allowing terrestrial radiation to pass into space, thus reducing the amount of heat available to warm the earth. Most climatologists reserve judgment. The evidence, they say, is too meager to prove that dust was the cause of the drought in the Sahel.

In their investigations of climatic change, scientists divide the possible causes into those that are generated on earth – such as volcanic activity – and those derived from forces beyond the atmosphere, as from the sun. Of the possible earthly causes, a particularly worrisome one to some climatologists is the so-called greenhouse effect, which traps the heat of solar radiation and warms the earth. The greenhouse effect is the result of the way two atmospheric gases, carbon dioxide and water vapor, act on solar and terrestrial radiation. Both of the gases are largely transparent to short-wave radiation, which includes ultraviolet and visible light, but they absorb long-wave, or infrared, radiation.

Most of the radiation reaching the earth from the sun is visible light, which passes through atmospheric carbon dioxide and water vapor and heats the earth’s surface. (The very-short-wave solar radiation is largely absorbed by oxygen or ozone higher in the atmosphere.) Thus warmed, the earth reradiates much of the energy received – but in the longer-wave, infrared range. Some of this infrared radiation escapes into space, but some of it is absorbed aloft by carbon dioxide and water vapor, and heats the atmosphere. The warmed atmosphere, in turn, emits more infrared radiation some back to earth and some out into space. The delicate balance between radiation gained and radiation lost by the atmosphere as a whole depends chiefly on the concentrations of the two gases. The total amount of water vapor present has apparently remained quite constant for as long as scientists have been able to measure it; the level of carbon dioxide, however, is a different matter.Carbon dioxide is released into the air by a number of natural processes, among them the burning or decaying of plants and the exhaling of breath by animals and humans. (Animals absorb oxygen from air and exhale carbon dioxide, while plants take in carbon dioxide and expel oxygen.) Analysis of such things as the air trapped in ancient ice indicates that the concentration of carbon dioxide in the atmosphere remained fairly constant for thousands of years.

Since the 19th Century, however, the level has been rising. One contributing factor was the clearing of forests to meet the insistent demand for firewood and tillable land; more carbon dioxide was released by the burning and decaying of the wood, and fewer living trees remained to absorb the gas. Another factor was the increasing use of fossil fuels. Now, with industrial output and the use of automobiles on the rise, the amount of carbon dioxide in the atmosphere is going up at an increasing rate: Scientists estimate that it increased by about 20 per cent between 1880 and 1980, and they think it will rise by at least another 10 per cent by the year 2000, and by still another 10 per cent in the 10 years following.

Accumulation of carbon dioxide presumably causes more absorption of infrared radiation – and thus more heat – in the atmosphere. But estimates vary on just how much average global temperatures might be affected. Some scientists think that readings might be up by almost 2°F. by the first part of the 21st Century, with an even steeper rise thereafter – assuming that some other factor does not counterbalance the heightened greenhouse effect. Other computations, however, indicate that the temperature increase may not be that great.

The oceans could help. They absorb even more of the gas than trees and other green plants (which may be growing more luxuriantly these days because carbon dioxide is more plentiful). In the past, ocean waters have apparently been able to absorb 45 per cent or more of the carbon dioxide added to the atmosphere. However, the process is hardly straightforward: Any increase in temperature would not only diminish the oceans’ capacity to absorb carbon dioxide, but would increase the rate of evaporation, and thus the amount of water vapor in the atmosphere. The greenhouse effect therefore could actually be heightened – although perhaps not right away: It would take a decade or two for a temperature increase to make itself felt in the upper layers of the ocean. Some of the keenest debates among climatologists arise when they try to assess the moderating role of the oceans.

Despite widespread concern about the greenhouse effect, scientists have no irrefutable proof that the increase in atmospheric carbon dioxide is in fact warming the earth. All predictions are based on laboratory studies and computer calculations. But a lack of conclusive data, as one climatologist has pointed out, “does not mean the theory is wrong.”

The formidable difficulties of calculating long-term climatic trends are illustrated by a consideration of the effect of clouds. Depending on their type, they may either raise or lower temperatures at the earth’s surface. Thin, wispy cirrus clouds, for instance, block relatively little incoming solar radiation but do inhibit the reradiation of heat from the earth, and thus tend to increase temperatures below. On the other hand, a low-lying canopy of stratus clouds can have the opposite effect: Since stratus clouds reflect more solar radiation and are also warm enough to radiate more heat back into space, they keep the earth’s surface cool in the daytime.

Climatologists are similarly uncertain about the overall importance to climate trends of the particles that pollute the atmosphere. Large particles, such as dust or smoke from fires, have little effect on long-term climate because most of them rise only as far as the lower troposphere and settle back to earth quickly. Small particles, known as aerosols, are another story. Since they are so small, they remain aloft longer and are carried farther from their source by winds, thereby affecting larger areas. While large particles settle within hours or, at most, days, aerosols can stay in the upper troposphere for weeks and in the stratosphere for months or years.

Tropospheric aerosols can either cool or warm the earth’s surface, depending on such factors as their size, chemical composition, shape and absorptivity. Stratospheric aerosols, however, tend to have a cooling effect on surface temperatures because they are too high up for the heat they gain by absorption to affect ground temperatures. No one yet knows when, or whether, the effect of man-made atmospheric aerosols might become truly significant in terms of climatic change.

The one type of atmospheric aerosol that scientists generally agree does produce some cooling is that spewed out of volcanoes. The dense clouds of dust, ash and gas rising from volcanic eruptions can reach into the stratosphere, travel around the world and linger for years, reflecting into space solar heat that would normally warm the earth. The British climatologist Hubert Lamb has gathered evidence that outbreaks of volcanic activity tend to coincide with cold periods. He found, for example, that there was an unusually high frequency of eruptions between 1500 and 1900, roughly the same time span as the Little Ice Age.

But the long-term effects of massive volcanic eruptions are, again, open to dispute. After years of intensive study, the Soviet climatologist M. I. Budyko concluded that a severe eruption yielding a particularly dense cloud could reduce the amount of direct solar radiation reaching the earth’s surface by 10 per cent for one to two years. Allowing for the different ways in which land and water absorb or reflect heat and for the circulation and dissipation of heat by the atmosphere, Budyko calculated that such an eruption could reduce temperatures the world over by as much as 1°F. The 1963 eruption of Mount Agung in Bali, for instance, is believed to have been responsible for an average decline of almost 1°F. in the tropics.

A few climatologists think that a long series of eruptions could conceivably initiate a full-scale ice age, but that scenario does not enjoy much scientific support. “There is no evidence,” states meteorologist Stanley Gedzelman, “that volcanic eruptions have ever produced any long-lasting climate changes. The only way for volcanic eruptions to do so would be if the level of volcanic activity was at least 10 times greater than it has been over the last century.”

The greenhouse effect, shown here in simplified form, occurs when carbon dioxide and water vapor in the lower atmosphere reflect heat that would otherwise be radiated out into space by the sun-warmed earth.

To identify forces that could produce long-term changes, many climatologists look outside the intricate, generally self-stabilizing and self-adjusting atmosphere, and consider what might be wrought by the sun or by the earth’s relationship to the sun. For if the entire atmosphere runs on energy coming from the sun, perhaps major climatic changes occur only if that energy supply fluctuates. The total amount of radiation reaching the earth from the sun is called the solar constant – a name that reflects the longstanding belief that it never changes. Evidence that began to emerge in the late 19th Century suggested that the assumption needed reexamining, and the clues were provided by sunspots.

These dark blotches on the surface of the sun, now known to be temporary intensifications of the solar magnetic field, were studied by Galileo in 1611 (he used them to calculate the speed of the sun’s rotation) and had been noticed centuries before that. But by the mid-19th Century, just about the only thing that was known about them was that the outbreaks reach a peak approximately every 11 years. Then the British astronomer E. Walter Maunder, combing through old records of sunspot sightings, found that for a period of 70 years – from 1645 to 1715 – almost no sunspots had been observed. They had shown up regularly before that, and they resumed thereafter. Maunder’s writings about this odd gap drew little attention until 1976, when U.S. climatologist John Eddy pointed out that the interlude, which he named the Maunder Minimum, coincided with a particularly severe period of the Little Ice Age.

The steady increase of carbon dioxide in the air is clearly documented in this chart of readings taken at an atmospheric-research station in Hawaii. The carbon dioxide level fluctuates widely each year because plants absorb the gas during the growing season, then release it when they decay in the autumn and winter.

Other scientists soon found more evidence of a connection between sunspot cycles and changes’ in climate. They discovered that sunspots in fact have a double cycle: Their frequency reaches a maximum about every 11 years, but the polarity of the sun’s magnetic field changes over a 22-year period. Climatologists studying tree rings, which are narrower in years of light rainfall, learned that droughts had recurred in the Western plains region of the United States approximately every 22 years. Other researchers found that, over the course of nearly five decades, the water level of Lake Victoria in Africa had risen and fallen in synchronization with the 11-year cycle. By the late 1920s, however, any connection that may have existed between sunspots and the lake ‘s water level was broken: The lake went completely out of phase with the 11-year cycle.

A solar prominence of flaming gases licks 370,000 miles into space, preceded by a coronal transient – a ballooning of the sun’s outer corona – visible in this composite photo. When coronal transients reach the earth’s magnetic field, they trigger enormous magnetic storms.

Climatologists believe it is possible that sunspots influence climatic change – though how, they cannot say. Spacecraft ranging far from earth have confirmed that sunspot activity affects the solar wind, the stream of electrically charged particles emitted by the sun. The earth ‘s magnetic field deflects most of these particles, but some manage to enter the upper atmosphere, where they collide with gas molecules and emit the shimmering lights of the aurora. In the early 1950s the American meteorologist Walter Orr Roberts made what seemed at the time to be a farfetched connection. Whenever the aurora borealis illuminated the winter skies above Alaska with unusual brilliance, he discovered, the low-pressure storm systems in the region became especially vigorous. His observations were confirmed, but after 1973 the mysterious relationship disappeared. No one has been able to explain either its existence or its absence.

Another possible extraterrestrial determinant of global climate operates so slowly that it could not cause such minor shifts as a drought or even a Little Ice Age. However, scientists believe it may be the principal mechanism of ice ages and warm periods thousands of years in duration. According to a hypothesis advanced in the 1920s by the Yugoslavian geophysicist Milutin Milankovitch, changes in the earth’s spatial relationship to the sun can bring about profound climatic changes simply by varying the amount and geographical distribution of solar radiation.

Milankovitch noted that as the earth spins and moves around the sun, both its orbit and its attitude change slightly. The orbit varies from almost circular to strongly elliptical and back again every 93,000 years or so. The earth’s tilt in relation to the plane of its orbit – the cause of earthly seasons – changes from about 22 degrees to more than 24 degrees and back every 41,000 years. The earth also wobbles, rocking in a circular motion around its axis like a slowing top, and this too has a cycle: One full wobble consumes 25,800 years. By altering the distance between the sun and earth or changing the angle at which radiation strikes particular points on the earth, these moves alter the amount of solar energy reaching certain latitudes in certain seasons.

Evidence that supports the critical role Milankovitch attributed to these cycles has accumulated steadily. For instance, scientists from the Lamont-Doherty Geological Observatory in New York discovered that variations in the type of oxygen and in the distribution of the remains of minute marine life – found in sedimentary samples taken from the floor of the Indian Ocean – indicate periodic and severe climate changes. The sea-core record suggests that some of these changes have peaked every 23,000 years, others every 41,000 years and still others about every 100,000 years. It seems highly unlikely that the similarity to the span of orbital variations is mere coincidence.

Because three factors are involved – orbit, tilt and wobble – their cumulative warming or cooling effects are extremely difficult to calculate. Even considered singly, the climatic effect is not easy to predict. Tilt, for example, affects the difference between winter and summer more than it affects the average global temperatures. For the past 10,000 years or so, the degree of tilt has been lessening, a process that should theoretically produce warmer winters but cooler summers. Warmer winters would mean more snowfall at the Poles; cooler summers would mean that less of the accumulated snow would melt each year, and more would remain to form glacier ice. After a period of years the polar ice sheets would increase significantly and eventually usher in a new ice age. Despite uncertainties about some details of the scheme, many climatologists are convinced that the Milankovitch model largely explains the recurrence of ice ages throughout the last million years or so of the earth’s history. And if the explanation is correct, it is almost inevitable that the earth will once again experience another ice age, perhaps within the next several thousand years.

Whether the earth is headed toward cooler or warmer times in the next several decades obviously cannot be decided with any degree of certainty. After the decline in global temperatures charted from the 1940s to the mid-1960s, the averages once again started inching up. During the same years George and Helena Kukla were reporting an increase in Arctic ice, the Antarctic ice pack was shrinking. Many climatologists are of the opinion that whatever trend is operating at the moment, the intensified greenhouse effect will probably overwhelm any cooling trend during the next half century or longer.

The dark blotches on this X-ray image of the sun are low-density holes in the sun’s corona. From these holes erupts the invisible stream of charged particles known as the solar wind.

Two of the most respected climatologists in the United States – William W. Kellogg and Stephen H. Schneider of the National Center for Atmospheric Research in Boulder, Colorado – have concluded “that mankind is likely to be warming the earth, and that the global climate change as early as the turn of this century could well be larger than any of the natural climate changes that we have experienced in the past thousand years or more. This will lengthen the average growing season in many places, and shift the rainfall patterns as well – some for better, some for worse .” William Elliott of the National Oceanic and Atmospheric Administration put it less formally: “If I had to make a prediction for the year 2025, I would say that it will be warmer than today. But I could be wrong, of course.”

Despite the uncertainty, advances in scientific knowledge about the atmosphere have, inevitably, spawned schemes to control the climate. Though such proposals ordinarily have some apparently laudable end, such as increased harvests, they all hold the possibility of unpredictable and irreversible damage to the earthly environment and to society as well. “Before we take comfort in our growing ability to bend nature to our purposes,” Stephen Schneider has written, “we must remember that the atmosphere, the oceans, the land surfaces, and the snow and ice fields-which are the major components of the climate system – all act in concert to determine the climate. The forces that generate winds and rain at one particular place on earth are coupled in varying degrees to those forces at places on the other side of the earth, a relationship meteorologists call teleconnections. Every place on earth is connected to some extent by the climate system to every other place.” Thus, as Reid Bryson has suggested, plunging temperatures at the North Pole can trigger monsoon failures in Africa and India and, simultaneously, drought in North America and endless rain in Europe.

A number of examples of what human interference with the earth’s teleconnections might bring are afforded by some recent large-scale engineering projects. Distressed by the low productivity of much of the grain-growing region in Siberia and vexed by the relentless Siberian cold, the government of the Soviet Union designed a plan to dam the Ob and Yenisei Rivers, which flow northward through Siberia to the Arctic Ocean, to create several large reservoirs for the irrigation of Siberian farmland. These artificial inland seas would also, it was thought, warm and moisten the winds blowing across them to the dry, frigid steppes beyond. Warmer temperatures and increased rainfall might well make previously barren steppe land fertile. Another part of the plan involved impounding several other rivers in north Russia and channeling some of the water to replenish the Caspian Sea, which has been shrinking in size and growing steadily saltier, thus harming caviar production.

Aside from the huge cost of the project, some analyses suggested serious potential problems. The resulting change in temperature and humidity could alter the Siberian high-pressure system, which exercises a strong influence on the weather in China and much of southern Asia. A chain reaction could affect not only the annual monsoons in Asia but conditions even farther away, such as rainfall in California and New York. Furthermore, depriving the Arctic Ocean of the fresh water contributed by the two rivers could impede the formation of sea ice, since the increased salinity would lower the freezing temperature of Arctic waters. A reduction in the expanse of ice would raise the temperature and the humidity in the Arctic sufficiently, said some climatologists, to increase the annual snowfall there – with still further unpredictable repercussions. Many Soviet scientists disagree with these scenarios and maintain that if the project is ever completed, it will affect only the Soviet Union.

Another scheme proposed by the U.S.S.R. – and reportedly even discussed by President Gerald Ford and Soviet Chairman Leonid Brezhnev at a 1974 meeting in Vladivostok – called for the construction of a dam across the 60-mile-wide Bering Strait between Siberia and Alaska. At first the idea seemed attractive. If warm Pacific water were kept from mixing with – and being chilled by – the cold Arctic Ocean, Siberia’s eastern shore and parts of Alaska would be warmer, ports currently unusable in winter would be ice-free and agriculture would spread farther north. But the reverberations would likely have been felt far away. If the dam allowed no water to pass into the Pacific, the icy polar waters would have to go in another direction and might drain across the top of North America and down Canada’s east coast, further cooling the already forbidding Labrador Current and shortening the growing season in Canada’s Maritime Provinces so much that agriculture might become nearly impossible.

The planners envisioned drawing the warm Gulf Stream northward into the Arctic basin to melt the polar pack ice. No one knows precisely what effects the melting of the ice would have on climate, but it is easy to imagine what might happen to the climate of England or Scandinavia, if the Gulf Stream was to desert its usual northeasterly course.

“At the present time, most meteorologists would agree that warming the Arctic by a small amount would change the global weather and climate,” wrote meteorologist and author Louis J. Battan in 1969 . “Unfortunately, nobody knows how it will change. Will the deserts be brought into bloom and the swamps dried up? Or will the swamps be even more inundated and deserts enlarged? Will the farming regions of the world get more or less rain and snow and when will it fall? Will the ocean surface rise and flood the low-lying cities of the world? Will the changes in general circulation initiate another ice age? No one yet knows the answers to these and a great many other related questions. Until we do, or at least can take a good guess, we better be careful tinkering with the global atmosphere.”

As if gazing into a scientific crystal ball, a researcher at an Australian meteorological station watches a parheliometer record information that might help to reveal climatic trends. Focussed by the glass sphere, the sun’s rays burn a record of each day’s solar radiation into calibrated cards mounted around it.

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