Marcos Brindicci / Reuters Pieces of ice fall from the Perito Moreno glacier in Argentina, December 16, 2009.
Foreign Affairs From The Anthology: Climate Wars
Explore the Anthology

What Might Man-Induced Climate Change Mean? [Excerpt]

Climate has always influenced human affairs. There are now increasing signs that man may in turn be altering global climate. This could change economic, political and even military relations among nations.

Climate drives agricultural and forest production, and it largely governs the way people live and work. Unexplained natural climatic variation has characterized all of human history and prehistory. Many climatologists now believe that in the present advanced stage of industrialization the addition of carbon dioxide and particulate matter to the atmosphere through burning of fossil fuels and clearing of land has become a significant agent of climatic change that could measurably raise the temperature of the earth by the end of this century. This would bring about appreciable shifts in the global pattern of activities dependent upon climate: agriculture, forestry, residential heating and cooling, water-dependent industry, recreation, and many more. It could affect the level of the seas.

Movement of climatic zones is likely to be at least as important as the global temperature change itself. The ultimate result of higher temperature, and of the more active atmospheric water circulation that will probably accompany it, could well be a net increase in global biological productivity. But the impacts will not be felt equally. Some regions and nations will gain; others will lose.

If the geophysical assumptions are correct, the process of climatic change due to industrialization is probably almost irreversible; the only practical strategy is adjustment. Technology will help to ease that adjustment, but the institutional rigidities of our advanced societies may correspondingly make the response to changed climate stickier than in earlier, simpler ages.

No one can yet say surely that the cumulative burning of fossil fuels at high rates will alter climate significantly. The answer lies at the end of a long cascade of uncertainties. There is uncertainty about the rates at which carbon dioxide, particulate matter, and other materials will be added to the atmosphere. How much will remain, and how much will be removed by physical and biological processes? There is still some disagreement whether additional atmospheric carbon dioxide will actually increase global temperature. If so, it is uncertain exactly how much temperature change will result from a given level of carbon dioxide. There is further uncertainty about how temperature change will be translated into shifts in global climatic zones. Ecologists are unable to say accurately how the postulated climatic shifts will affect cultivated and noncultivated plant and animal communities. And the social and political implications are still more problematical.

Yet none of the uncertainties is absolute. Estimates, within some range of error, can be made for each. The sum of these estimates suggests a fairly high probability that measurable man-induced climatic change is in the offing. Thus, it seems worth taking a look at the possible long-term implications for human institutions.

II

Projections based on anticipated annual burning of fossil fuels, and on the fraction of the resulting carbon dioxide expected to remain in the atmosphere, lead to forecasts that atmospheric concentrations of carbon dioxide will range between 375 and 400 ppm by the end of this century. These models attempt to estimate cumulative levels of unabsorbed carbon dioxide under several plausible scenarios of future use of fossil fuels (coal, of course, as well as oil and gas). All assume a steady growth, at alternative rates, in overall consumption. The best analyses indicate that a doubling of the preindustrial level can be expected sometime between 2020 and 2040, depending upon which of the alternative use rates finally prevails.

These models assume that the earth's plant cover - the biosphere - is constantly taking up some of the added carbon dioxide through increased growth, or at least is not adding to the total in the atmosphere. However, recent analyses present several lines of evidence that the biosphere is actually a source of carbon dioxide about as large as the fossil fuel source. The reason is that net destruction of plant life and soil organic matter releases carbon dioxide. The new analyses suggest that the rate of forest clearing, particularly in the tropics, is much greater than had previously been suspected. This conclusion is still controversial. If it is correct, a doubling of atmospheric carbon dioxide would be much closer in time. This is an example of the kind of uncertainties that can be reduced only through a concerted international effort.

Whatever the time scale, how will the projected increase in carbon dioxide translate into changes in global temperature? Because of the complexity of competing processes in the atmosphere, it is impossible to use direct observations, relating historic temperature changes to the known historic increases in atmospheric carbon dioxide. Resort must be to complex calculations based on radiation properties of atmospheric gases and the observed structure of the atmosphere. Even the most realistic of these models involve many unknown factors, omit important feedback mechanisms, and require much computer time for their solution.

The most generally accepted models all predict that increased carbon dioxide will produce an increase of temperature near the ground. The temperature response is nearly logarithmic; that is, each proportionate increase in the concentration of carbon dioxide produces about the same absolute increase in global temperature. Stephen Schneider of the National Center for Atmospheric Research has critically reviewed the models in existence up to 1975. He concluded that those which best reflect current geophysical knowledge converge on an increase of between 1.5°C and 3°C for each doubling of carbon dioxide - the increase predicted in 2020 to 2040, roughly 40 to 60 years away - with lesser increases appearing in the meantime. Small as such changes may appear, they are enough to make a substantial difference in many economically important processes at the earth's surface, as will be seen later.

The general neglect of feedback mechanisms for clouds and ocean circulation in these models opens the possibility that the estimates may be substantially in error in either direction. However, Schneider concluded that there is no strong evidence that present models are more likely to overestimate the rise than to underestimate it.

There is one major problem with these model estimates. They do not precisely accord with observations over the last century. Careful analysis of worldwide temperature records indicates that global mean temperature apparently rose by a total of about 0.6°C between 1850 and 1940. Since then, instead of continuing to increase as would have been predicted by the carbon dioxide theory, temperatures have apparently dropped about 0.3°C to the present. Some climatologists believe that since about 1971 global mean temperature has been increasing again, but this is too short a time to firmly establish a trend.

A number of respected atmospheric scientists cite the lack of warming during the industrial era since 1940 as strong evidence that the postulated effect is not important, and that global cooling still predominates. However, the occurrence of an apparent trend contrary to that predicted by theory, even over a period of 30 years, is in itself neither surprising nor a refutation of the theory.

Temperature fluctuations, up or down, of 1°C or more per century throughout the past have been inferred from a variety of historical and paleoecological records. It is easy to argue that the period 1940-70 was one of normal cooling, on which was superimposed some warming due to the carbon dioxide effect. The cooling was therefore less than it would have been in the absence of industrial carbon dioxide. The verdict must remain "not proven." But if the warming effect of carbon dioxide over the next 40 to 60 years should be toward the higher (3°C) range in the models reviewed by Schneider, its magnitude would far outweigh the apparent 1°C range of normal fluctuation, even assuming that the latter continues to be in the direction of cooling.

III

What is clear is that any warming that does occur will not be uniformly distributed. That is one point on which all the experts seemingly agree. Both the climatic simulation models and past observations confirm this estimate.

Temperature increases will be greater at high latitudes than near the equator. This is borne out by experience during warming and cooling trends in the past century. A 1°C increase in global mean temperature might result in a change of 0-0.5° between 10°N and 10°S latitude, 2-4°C at 60°N and 60°S latitude, and even more than that closer to the poles. The impact of a 2°C mean increase would be roughly twice as great, and so on.

This is important in two ways. In the first place, the tropics, already near the limits of tolerance for many organisms including man, will not become unbearably hotter even in the face of a considerably higher mean temperature. Neither is there likely to be much change in precipitation in the wet tropics. The greatest impact in the equatorial zone is likely to be a second-order one, resulting from changes in demand and prices for agricultural exports and imports, due to climatically induced economic changes elsewhere.

At high latitudes, on the other hand, both agricultural productivity and general livability are likely to be improved, particularly where the length of the growing season is now marginal or sub-marginal for crop production. Of the great subarctic land masses, those in the Soviet Union would appear to stand a better chance of reaping significant benefits than those in Canada or Alaska or the Scandinavian countries. The reasons for this conclusion will be considered in more detail below.

This is a good point at which to consider the impact of higher poleward temperatures on the polar icecaps and on sea level. A complete melting of glacial ice, almost all of which is in Antarctica, would raise the level of the oceans by more than 50 meters, but this is most unlikely on a time scale of less than many centuries, if then. Even with a polar warming of several degrees, air temperatures over Antarctica would still be below freezing most of the time. Furthermore, dry air alone is a relatively inefficient melting agent compared with solar radiation, which would be little altered.

More complex scenarios can be visualized. Some have suggested that a moderate warming of the Antarctic ice, without melting, would accelerate glacier flow and discharge of ice into the ocean. Or warm polar water could induce a flow of ice from the continental shelf into the sea, possibly raising sea level by five meters in 300 years. A rise of much smaller magnitude could be catastrophic for a nation such as the Netherlands, but this does not seem a major near-term threat.

Melting of the Arctic ice is perhaps slightly more likely. The North Polar ice floats on the Arctic Ocean, fluctuating in thickness from about 15 meters in winter to sometimes no more than a meter or two in summer. Because it is already floating, its disappearance would not alter sea level, but there could be drastic and unpredictable climatic feedbacks. An open ocean would absorb more solar radiation than ice. The Arctic Ocean has apparently not been open for the last million years or so, yet it appears that the Arctic ice could in fact be melted under some circumstances.

As important as shifts in temperature bands may be changes in the pattern of precipitation, particularly the subtropical monsoon. From the equator to the poles, the earth is roughly characterized by an equatorial zone of heavy rainfall, a rather abrupt transition to a belt of deserts and semideserts, a relatively moist zone of prevailing westerly winds in the temperate latitudes where most of the world's advanced nations are concentrated, and increasing dryness toward the poles. This general pattern is greatly modified by continental land masses.

The annual monsoon is particularly important to some of the world's less-developed nations. During summer, the zone of moist tropical air moves north, bringing heavy rainfall to the Indian subcontinent and lesser but still essential amounts to much of Africa south of the Sahara. When the monsoon rains are abundant, crops and water supplies are plentiful. When they fail, hardship follows, as evidenced by the widely publicized drought in the Sahel region of sub-Saharan Africa in the early 1970s.

Reid Bryson of the University of Wisconsin has shown that the position of the boundary between moist monsoon air and dry desert air is extraordinarily sensitive to small changes in the north-south temperature gradient. What apparently happens is that when polar temperatures are relatively warm, there is a strong pattern of global circulation, and the north-south oscillation of the westerly winds that sweep around the temperate regions is confined within a relatively narrow range of latitudes. Farther south, however, the tropical wind patterns are pulled well to the north, and allow the monsoon rains to reach high latitudes. Historically, this kind of strong circulation and northward penetration of the monsoon seems to be associated with unusual warmth throughout the northern hemisphere. This is at least suggestive that the same may happen as a result of general global warming. The monsoon areas of the world could thus be substantial gainers from the climatic effects of worldwide industrialization.

In the mid-latitudes, on the other hand, the effect is more mixed. There the north-south oscillation of the westerly winds largely governs the distribution of precipitation. When global circulation is relatively weak, it is easier for large masses of cold air to spill southward, where they meet warm subtropical air and increase precipitation. Warm air is then forced northward in spinning storm systems that move eastward through the temperate latitudes. With the stronger circulation patterns associated with polar warming, these oscillations tend not to push so far south. Rainfall over the Mediterranean region and the Middle East is suppressed, and there tends to be higher than normal precipitation in the British Isles and at similar latitudes.

Because evaporation is related to temperature, global warming would tend to create a greater flux of water vapor from the land and oceans into the atmosphere. Computer models suggest that the degree of warming estimated from a doubling of carbon dioxide could increase total global precipitation by an average of about seven percent. Again, such an increase would not be uniformly distributed. Much of the added moisture might fall back into the ocean.

Finally there is the factor of variability. What we call climate is just the average, over months and years, of individual weather events. Even if world climate should become warmer and wetter, there will still be cold spells and dry spells, as sharp as in the past. These will be overshadowed, though, by more frequent and perhaps more marked warm episodes.

Neither will all parts of the world warm simultaneously. Historical experience clearly indicates that warm periods in one part of the world will be accompanied by cold in another, just as the bitter winter of 1977 in the eastern United States was matched by the warmest weather in a century in Vienna.

Year-to-year weather variability is important to human comfort, to industry, and to agricultural productivity. Agriculture and industry can more easily adjust to changed conditions if the new weather regime is relatively uniform from year to year. Increased variability makes agriculture in particular a more uncertain venture. Opinions - evidence is too strong a word - differ as to whether global warming will mean more or less climatic variability. The preponderance of opinion seems to be that the increased intensity of global circulation will bring with it the possibility of more frequent and larger deviations from the mean. Fluctuations in agricultural production, and consequent wide swings in grain prices and markets, could follow. The effect on global and national economies and on inflation rates of similar swings in the early 1970s are a vivid memory.

IV

The emphasis so far has been on global warming through increased atmospheric carbon dioxide. At least two other potential human impacts on global climate could be influential: discharge of particulate matter and release of heat into the environment from burning of fossil and nuclear fuels (called heat emission).

The transparency of the global atmosphere, as measured at many places, is steadily decreasing due to continued addition of fine particles. These arise chiefly from three man-made sources and one natural: burning of fossil fuels, wind-borne agricultural dust, and smoke from slash-and-burn agriculture in the tropics, plus intermittent injections into the stratosphere of debris from major volcanic eruptions. Particles reflect and scatter solar radiation back to space, reducing the amount available for heating of the surface. They also absorb solar radiation, and thereby heat the atmosphere. Recent evidence suggests that the second effect predominates in the lower atmosphere, at least up to the point where particle loading would be a serious health hazard. Although the impact of particulate matter on global climate is not negligible, the Energy and Climate Panel of the National Academy of Sciences concluded that man-induced particulate loading is unlikely to increase to the point that it is a serious threat in this respect. (The blunt fact is that, before then, impacts on human health and on agricultural productivity would require stringent control measures.)

The panel reached similar conclusions with regard to the impact of heat emission on climate. Even a future world population of ten billion people, with a per capita energy use several times greater than at present, would release an amount of heat equivalent to only a thousandth of the daily radiation received from the sun. If evenly dispersed, this would have little measurable effect on climate.

Concentrated heat emissions could, however, trigger changes in climate if, as some atmospheric scientists believe, global circulation is sensitive to small changes in inputs at crucial times and places. That this may be so is suggested by computer simulation experiments carried out by the International Institute for Applied Systems Analysis (in Vienna) and the United Kingdom Meteorological Office. Economically significant changes in simulated temperature and rainfall were indicated almost everywhere in the northern hemisphere as a result of concentrated heat discharge from assumed large "energy parks" (specifically, centers for the production and distribution of electricity). The present models do not simulate climate in a fully realistic way, so that these results must be interpreted cautiously. Other climate simulation models, when more fully developed, should permit better prediction of the effects of carbon dioxide increase and also help to give better answers to the questions raised by heat emission.

A further reason for giving most attention to carbon dioxide is that its climatic effect, if real, will be less reversible than that of the other two factors. Particles in the troposphere - the layer of the atmosphere where active weather processes occur - have a mean residence time of perhaps 10 days. They stay a bit longer in the stratosphere, three years or so. In either case, stringent measures to reduce particle emission would be reflected in the atmosphere in weeks or at most years. The same is true of concentrated heat sources, which could be turned off instantly if one was willing to disregard other social consequences.

Carbon dioxide is different. Even if burning of fossil fuels were suddenly to be banned all over the world - a far-fetched possibility - it would take decades, maybe centuries, for the concentration of carbon dioxide in the atmosphere to decrease significantly.

VI

Carbon dioxide enters the atmosphere from so many sources that any effective social control of its emission on a global scale is most unlikely. As a practical matter, it is stoppable only at the source, by worldwide prohibition of coal mining, peat cutting, and extraction of oil and natural gas. Short-term economic and social consequences are almost sure to rule out the required unanimous international consent. Fossil fuels are so convenient for so many purposes, and so easily extracted, that they are almost certain to be used to the limit of their availability even if there should be a global commitment to emphasize nuclear, solar, and geothermal energy resources in their place. As we have already noted, because of the long residence time of excess carbon dioxide in the atmosphere, even an appreciable decrease in the rate of fossil fuel burning will only delay the time of maximum climatic effect. It will not prevent it.

If the world community is unwilling or unable to take the stringent measures necessary to stop carbon dioxide emission, society must simply adjust to changing climate. Technology may aid in that adjustment, but it also may make the transition more difficult. Witness how a moderate snowfall, little more than a minor inconvenience a couple of generations ago, ties up an automobile-bound modern city.

Technology and social patterns will influence the way that human institutions react to climatic change. The extinction of the Norse colony in Greenland during the medieval cooling period is unlikely to be duplicated in an era of rapid communication and efficient transportation. One can surmise, though, that the death of the Norsemen was due in part to their unwillingness or inability to adapt to the subsistence techniques of the native population, which did survive. How much more adaptable are modern societies?

The widespread suffering during the Sahel drought of the early 1970s is at least indicative of the ways in which new technology and social change can make whole populations more, not less, vulnerable to climatic shifts. The nomadic livestock culture of that part of Africa was well adapted to periodic drought. Livestock were pastured near the few permanent watering places during dry periods, and dispersed throughout the region during wet weather. This natural rotation allowed recovery of the forage around the permanent water holes when the nomads left them, and conversely permitted regrowth of the more distant vegetation during the time that animals were concentrated around the water.

In an effort to provide for more livestock, a need brought about in part by increased population due to newly introduced public health measures, deep wells were drilled throughout the region. This permitted wider dispersion of livestock at all seasons, and increased the number that could be supported, at least for a time. The resultant overgrazing led to depletion of the forage resource, which could not recover as it had in the past because the natural rotation cycle had been broken. So when the monsoon failed for several years in a row, first livestock and then people starved.15 It is not at all certain that the actual percentage of the human population affected was greater than in past droughts, but there is no question that a larger absolute number of people faced malnutrition and starvation than in previous episodes.

This somewhat oversimplified account of an extreme case in a region where development was just beginning may not be representative of the situation in the industrialized world, but it is illustrative. Will social institutions in more developed regions endeavor to resist and counteract the effects of climatic change, or will they flow with the tide, making incremental adjustments as they go? The former strategy might work for a while, but eventual disruption and breakdown would seem inevitable. The difference may be important for the peace of the world.

VII

Not only is there great uncertainty about the nature and magnitude of the consequences of global warming, but its principal effects will be felt only in decades to come. Yet actions taken, or not taken, today are likely to affect significantly our children and grandchildren. What is our obligation to future generations, and how shall that obligation be carried out? That is of course an age-old question; the difference now seems to lie in the scope and rapidity of human impact on the globe. Man has apparently become a major geological and geophysical agent in his own right, able to influence the physical and biological conditions of the future, deliberately or inadvertently, in a way not open to our ancestors.

There is an urgent need for intensified research to limit some of the uncertainties which now make informed political choice almost impossible. We must learn more about the carbon cycle itself, particularly the quantitative fluxes of carbon dioxide between the atmosphere and the land and between the atmosphere and the oceans. We must be able to predict more accurately the climatic effect of increased levels of atmospheric carbon dioxide. This is now the major uncertainty in assessing the environmental impact of fossil fuel consumption. We must also learn to anticipate the ecological, economic, social, and political consequences of climatic change. This is a formidable interdisciplinary and international research task whose dimensions are only beginning to be seen. There are heartening indications of a growing international consensus on the need for cooperation to provide solutions.

But research can be only a prelude to action. What actions are called for, or even possible?

In a talk before the American Physical Society, Thomas Moss, principal assistant to Representative George Brown, Chairman of the House Subcommittee on Environment and Atmosphere, pointed out that climatic change is a virtual prototype of a problem poorly matched to existing human institutions. Its time span is longer than a political leader's career. The potential effects are enormous, conceivably dwarfing those of normal man-made technical and social change. This kind of problem presents an almost insurmountable challenge to institutions designed for times when societies were less complex, man's abilities for doing "good" and "bad" much more limited, and thinking more restricted in time and space.

In both its spatial and temporal aspects, global climatic change stands almost alone among the world's environmental problems. Many pollution and natural resource issues do not respect national boundaries, but the carbon dioxide question is unique in that regardless of how much sources may be localized, the atmospheric concentrations will be the same everywhere. It is likewise unique in that its impact will persist long after the sources are eliminated.

And unlike most environmental impacts, this one could in the long run appreciably benefit some nations and regions while harming others. This will make international consensus even more difficult than with other forms of environmental change. Essential to a global consensus is a better understanding of the causes and consequences of climatic change, an understanding that can come only through a truly international multidisciplinary effort. [Full Article]

Related Articles

This site uses cookies to improve your user experience. Click here to learn more.

Continue

Close We are offering free and open access for a short period of time. Read more about why we are doing this.

Days
Hrs
Min
Sec