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From page 5...
... Concern arises about human activities that release greenhouse gases because important absorption bands for CO2 and other atmospheric gases are far from saturation; increasing the concentration of the gases will continue to affect the net emission or absorption of energy from a given layer of the atmosphere and thus the climate. The second fundamental point is that the atmospheric concentration of C02 is rising.
From page 6...
... We talk about American agriculture in the year 2000, global energy use to 2l00, and possible changes in sea level over the next three to five centuries. Is it meaningful to talk of such remote times?
From page 7...
... u n o -H 1M ecu.
From page 8...
... Are CO2-induced climatic changes already identifiable? What would be the effects of substantial warming induced by increased atmospheric concentrations of CO2 and other greenhouse gases on agriculture, water supply, and polar regions and sea level?
From page 9...
... The United States accounts for about one quarter of worldwide fossil fuel emissions, as do Western Europe and Japan, the Soviet Union and Eastern Europe, and developing countries. To estimate future emissions of CO2 from fossil fuels, Nordhaus and his co-authors adopted two approaches.
From page 10...
... This range contrasts with the 4.3% figure for past and projected growth in CO2 emissions that prevailed for several years in the literature on the CO2 issue. The mean growth rate of fossil fuel C02 emissions over the past l20 years has more recently been estimated at about 3.5% per year (Elliott, l983)
From page 11...
... ll 8 (uoqjeo jo 8 8 SNOISSII/\I3 N08dVD o «tr < 01 § •H -U B o k i O
From page 12...
... and to respect the cost and availability of fossil fuels. The analysis attempts to recognize explicitly the intrinsic uncertainty about future developments by identifying the most important uncertain parameters of the model, by examining current knowledge and disagreement about these parameters, and then by specifying a range of possible values for each uncertain parameter.
From page 13...
... The World Climate Programme (l98l) group of experts adopted a range of 50 to l50 Gt of C for biospheric emissions in the l980 to 2025 period.
From page 14...
... , carbon dioxide is well mixed in the atmosphere; measurements from the global network of sampling sites show relatively small spatial and temporal variations that are explainable largely in terms of fossil fuel sources
From page 15...
... The year-to-year increases in atmospheric concentrations are generally becoming larger with time, roughly in step with emissions of CO2 from fossil fuel combustion. Indeed, according to Machta (this volume, Chapter 3, Section 3.4)
From page 16...
... reports several estimates that give a value at the present time of about 2 Gt of C/yr, or 40% of fossil fuel emissions. The terrestrial biota and soils contain about three times as much carbon as the atmosphere, and their changes could influence the atmospheric burden.
From page 17...
... See Brewer, Chapter 3, Section 3.2 for further explanation. plausible that future changes in the atmosphere could lead to a significantly increased net biotic flux of carbon to or from the atmosphere.
From page 18...
... , apparently because of mixing with air from over the oceans. Fossil fuel emissions are included for comparison.
From page 19...
... . In the last few years, carbon cycle models, like energy models and climate models, have become more sophisticated.
From page 20...
... On the other hand, if net releases of CO2 from the biosphere comparable to those from fossil fuels are now in progress and have been for the past several decades, the question of carbon-cycle modeling is different. If, for example, C02 released annually from deforestation were in the upper part of the range that Woodwell suggests, the current models would fail to reproduce the observed atmospheric C02 growth TABLE l.l Sensitivity Study Using a Box Model of the Carbon Cycle (Keeling and Bacastow, l977)
From page 21...
... For a quarter or half century, the inertia built into the world economy and carbon cycle leaves an impression of relative certainty about outcomes. After the early part of the next century, however, the degree of uncertainty becomes extremely large.
From page 22...
... See Nordhaus and Yohe, Chapter 2, Section 2.l, and Figure 2.l8 for further detail. On this result, Nordhaus and Yohe base a central conclusion: Given current knowledge, odds are even whether the doubling of carbon dioxide will occur in the period 2050-2l00 or outside that period.
From page 23...
... is at the top of the list; several of these parameters have rarely been noted as factors affecting future CO2 trends. Another surprise concerns two parameters that have been extensively discussed in the CO2 literature: the extent of world resources of fossil fuels and the carbon cycle (based on a range for the airborne fraction of between 0.38-0.59)
From page 24...
... If the rate of emissions from fossil fuels is slower, then biotic emissions could account for a somewhat more significant share of overall increase. Nordhaus and Yohe have also made extremely tentative estimates of the effect of energy-sector policies designed to reduce the burning of fossil fuels, in particular the imposition of fossil fuel taxes, set for illustrative purposes at $l0 per ton of coal equivalent.
From page 25...
... Thus, the growth in atmospheric concentration from these sources might continue for many decades but perhaps not for many centuries. Methane also forms another link in the question of future atmospheric composition.
From page 26...
... The atmospheric concentrations of these trace gases are not all independent of one another. Complicated chemical reactions among them, as well as with other gases not particularly radiatively active, can affect their concentrations.
From page 27...
... . Comparisons of simulated time means of a number of climatic variables with observations show that modern climate models provide a reasonably satisfactory simulation of the present large-scale global climate and its average seasonal changes.
From page 28...
... FIGURE l.ll Schematic illustration of the components of the coupled atmosphere-ocean-ice-earth climatic system. The solid arrows are examples of external processes, and the open arrows are examples of internal processes in climatic change.
From page 29...
... . Investigations with a variety of climate models continue to show a broad range of estimates of appreciable warming.
From page 30...
... Unfortunately, we cannot at present predict the magnitude and locations of regional climate changes with much precision or confidence. Although current models are not sufficiently realistic to provide reliable predictions in the detail desired, they do suggest scales and ranges of temporal and spatial variations.
From page 31...
... It is worth noting that because the concentration of each of these gases is small enough for their radiative effect to be treated as optically thin, the temperature effect is linearly proportional to TABLE l.4 Some Estimates of Surface Temperature Change Due to Changes in Atmospheric Constituents Other Than CO2 Mixing Ratio Change Surface (ppb) Temperature Constituent From To Change (°C)
From page 32...
... These studies can be useful in exploring the sensitivity of climate to various factors, in evaluating how well climate models perform, and in exploring the kinds of regional patterns of change that are possible. However, the search for a historical analogue to C02-induced climatic change is hampered by inadequacies in data and by the absence of close parallels of cause and effect.
From page 33...
... To the extent that one can judge from scanty data, southern hemisphere temperatures have increased more steadily than in the north by about the same total amount. In view of the relatively large and inadequately explained fluctuations over the last century, we do not believe that the overall pattern of variations in hemispheric-mean or global-mean temperature or associated changes in other climatic variables either confirms or contradicts model projections of temperature changes attributable to increasing atmospheric CO2 concentration.
From page 34...
... The success achieved by several workers in explaining the temperature record in diverse ways demonstrates that a number of hypotheses can fit the poorly defined historical data and estimated preindustrial concentrations. The available data on trends in globally or hemispherically averaged temperatures over the last century, together with estimates of C02 changes over the period, do not preclude the possibility that slow climatic changes due to increasing atmospheric CO2 projections might already be under way.
From page 35...
... concentration of C02- The ordinate represents the increase (AT) in global mean equilibrium surface temperature between l850 and the period l96l-l980.
From page 36...
... For purposes of analysis, in the next three sections we accept the estimates from models for C02 emissions, concentrations, and climate change and examine their implications for agriculture, water resources, and sea level and polar regions. For examination of agriculture, Waggoner looks ahead about 20 years and adopts maximum assumptions of change: about 400 ppm and a l°C warming.
From page 37...
... However, most effects of CO2 on photosynthesis and plant growth have been studied and measured during short periods when other factors such as light, water, temperature, and nutrients were adjusted to an optimal level. In addition, growth habits and adaptations to different environments might alter the effects of changing CO2 concentration.
From page 38...
... . If we assume no significant adaptation of inputs and limited geographic mobility, the warmer and drier climate assumed to accompany the increased C02 will decrease yields of the three great American food crops over the entire grain belt by 5 to l0%, tempering any direct advantage of C02 enhancement of photosynthesis.
From page 39...
... . affected, if, as indicated by climate models, temperatures change little there.
From page 40...
... l.2.7 Sea Level, Antarctic, and Arctic Many processes can cause an apparent change in sea level at any particular location. They include local or regional uplift or subsidence of the land; changes of atmospheric pressure, winds, or ocean currents; changes in the volume of the ocean basins owing to volcanic activity, marine sediment deposition, isostatic adjustment of the Earth's crust under the sea, or changes in the rate of seafloor spreading; changes in the mass of ocean water brought about by melting or accumulation of ice in ice sheets and alpine glaciers; and thermal expansion or contraction of ocean waters when these become warmer or colder.
From page 41...
... Indeed, the present is a time of quiet sea level compared with the violent oscillations that occurred during roost of the last l00,000 years. The projected climatic warming from increasing atmospheric CO2 and other greenhouse gases will lead to an increased transfer of water mass to the sea from continental (Greenland and Antarctic)
From page 42...
... Of even greater uncertainty is the potential disintegration of the West Antarctic Ice Sheet, most of which now rests on bedrock below sea level. This could cause a further sea-level rise of 5 to 6 m in the next several hundred years.
From page 43...
... If the time required for the ice shelves to disappear is l00 years, Bentley1s analysis would not be incompatible with a minimum time of 300 years for disintegration of the West Antarctic Ice Sheet. The corresponding average rate of rise of sea level would be slightly less than 2 m/l00 years, beginning about the middle of the next century.
From page 44...
... l.3 SERIOUSNESS OF PROJECTED CHANGES In assessing the seriousness of the changes projected in the preceding sections, there are two enormous sources of uncertainty. One source is the contents of the above outlook itself: uncertainties about sources and uses of energy, which in turn embody uncertainties about population, per capita income, energy-using and energy-producing technologies, density and geographic distribution of populations, and the distribution of income; a multitude of uncertainties about the carbon cycle; uncertainties in translating a growth curve for C02 in the atmosphere into appropriately time-phased changes in climate in all the regions of the globe; uncertainties about whether human activities other than release of C02 will be affecting the climate and what "natural" climatic trends will be; and, finally, uncertainties about effects on plant growth, water supplies, sea level, and other factors.
From page 45...
... Seeking higher yields and more profit, farmers will correct their course annually, and they may even adapt to a slowly changing climate unconsciously and successfully. Thus, we do not regard the hypothesized CO2-induced climate changes as a major direct threat to American agriculture over the next few decades.
From page 46...
... . The impact would be especially severe in the Missouri, Rio Grande, Upper Colorado, and Lower Colorado regions where even current water requirements would exceed the supplies after climatic change by between 20 and 270%.
From page 47...
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From page 48...
... Resuming the question of sea level, we concluded above that with a postulated warming of about 3 or 4°C from CO2 and other greenhouse gases a gradual rise is probable over the next l00 years as a result of thermal expansion of the ocean, ablation of the Greenland and Antarctic ice caps, and retreat of alpine glaciers. We have also mentioned that, because of events in Antarctica, a much larger rate of rise is not unlikely during the following several centuries.
From page 49...
... It is therefore worth emphasizing that there are ways to defend against rising sea levels. For built-up and densely populated areas, defenses could be cost effective for a rise of as much as 5 or 6 m.
From page 50...
... And, climatic shifts may change the habitats of disease vectors or the hosts for such vectors. l.3.3 The Problem of Unease about Changes of This Magnitude Enveloping our specific and more speculative concerns about impacts of climatic change on water resources, sea level, and other areas discussed is a profound uneasiness about inducing environmental changes of the magnitude envisaged with major increases in atmospheric CO2 and other greenhouse gases.
From page 51...
... Disappearance of the permanent Arctic ice would result in a marked increase in the thermal asymmetry of the planet, with only one pole still glaciated. Such asymmetric conditions could produce further, unanticipated climatic changes (Flohn, l982)
From page 52...
... ! 1.0 08 10' YEARS AGO •C 131.0 08 '.0s YEARS AGO FIGURE l.l4 An approximate temperature history of the northern hemisphere for the last 850,000 years.
From page 53...
... At the same time, one might observe that -- barring the kind of surprises mentioned above -- the climate changes under consideration are not large in comparison with the climate changes individuals and social groups have undergone historically as a result of migration. Table l.l0 shows U.S.
From page 54...
... 54 41 co § 3 I 3 s s 5 O M O M O -H 4J U m H I I
From page 55...
... fossil fuels to help effect the change. The marginal effects of climatic change on the distribution of wealth may range from quite positive to quite negative.
From page 56...
... In contrast, water resources are usually regional or local. Worldwide agreements involving some of the main consumers or producers of fossil fuels would be
From page 57...
... 57 essential to programs for reducing CO2 emissions; in contrast, water development and conservation are national in scope or involve a few neighboring countries. l.4.2 The Organizing Framework If we accept that the issue is climate, then it follows that the organizing framework for welfare and policy implications of atmospheric CO2 should also be built around climate change, not around CO2.
From page 58...
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From page 59...
... 0 -c •o 4J » A a e 41 in m ? - € •H §„ Si 8 n -H m m ^3 iM SS OJ to rH u 4J i0 k i ^ 01 i0 4J « a Agriuulture, laed use, Farmieg and dust Agriuultural (NjO, CH4 Water supply, teuheology, coeservatiol sourues (iu desalinizat ^Responses ma; Goveremeets rH rH -H > » 10 (MCO a a.
From page 60...
... Impacts of climatic change could, of course, be numerous and diverse, affecting agriculture and water supply, ecosystems, and location of industry, for example, and adaptive response could thus take numerous forms, from writing assessment reports (studying the problem)
From page 61...
... Although the prospect of historically unprecedented climatic changes is troubling, the problems that may be associated with it are of quite uncertain magnitude, and both climate change and increased C02 may also bring benefits. There are theory and evidence for each link in the chain of causal inference that we have described, but it could be that emissions will be low, or that concentrations will rise slowly, or that climatic effects will be small, or that environmental and societal impacts will be mild.
From page 62...
... And, similarly, responses that might be useful with respect to C02-induced climatic changes -- such as reducing water demand or increasing water supply in the Great Plains of the United States -- might be appropriate responses to other problems, like depletion of the Ogallala Aquifer. Attitudes toward CO2 may be different if one treats it jointly with other issues; policies judged expensive for one issue might seem more affordable as responses to a combination of issues.
From page 63...
... It is not too soon to begin to think of ways in which the planned use of water could alleviate potential effects of climatic changes or even take advantage of them. Several possible measures come to mind: changes in legislation that would allow water to be transferred from one river basin to another; improved efficiency in the use of water for irrigation; conservation of waste water and of municipal water supplies; limitations on the size of irrigated areas; increases in crop yields per unit volume of applied water; and enhancement of the recharge of aquifers (Revelle, l982)
From page 64...
... Our study does, however, suggest that considerations of the ease of substitution between fossil and nonfossil fuels and between energy and labor inputs in the economy, along with extraction costs of fossil fuels, and the bias of technological change in the energy sector are of great importance in determining future emissions, which will account for considerable variance in atmospheric concentration over the next century. Thus, we conclude that l.
From page 65...
... However, our current assessment of the probability of an alarming scenario justifies primarily increased monitoring and vigilance and not immediate action to curtail fossil fuel use.
From page 66...
... l.5.5 Applied Research and Development The prospect of climate change clearly lends urgency to applied research and development in two areas besides energy: agriculture and water resources. Although no detailed timetable of climatic change is yet available, we have some notion of the general character of the climatic challenges that may be ahead of us.
From page 67...
... Where this water exists in aquifers that are easily rechargable, it represents a potentially permanent addition to water supplies. White pointed out that the techniques have been of major importance in developing countries that can use them to gain access to previously untapped supplies without building elaborate storage and conveyance works.
From page 68...
... Rather than stress the need to attack any particular link in the CO2 argument, we stress the need for balanced attention to the major components: emissions, concentrations, climate change, and environmental and social impacts and responses. A plethora of research recommendations exists, and several areas, for example, the carbon cycle and climatic effects, are being pursued with considerable vigor.
From page 69...
... 5. Human-induced climatic change and the CO2 issue more generally are not problems for which traditional paradigms of policy analysis and methods of assessment, like those taken from economics, engineering, and decision analysis, have had much success (Glantz et al., l982)
From page 70...
... Although politicians may have one eye on posterity, political systems tend to be myopic and to emphasize short-term rewards. Given the need for widespread, long-term commitment, a CO2 control strategy could only work if major nations successfully negotiated a global policy.
From page 71...
... The United States should contribute energetically to this effort from both governmental and nongovernmental communities concerned with studying and responding to the prospect of a CO2-induced climate change. It is worth noting that on particular issues, like detection of a CO2-induced climatic change and evaluation of climate model results, there may be considerable efficiency in having an international focal point.
From page 72...
... 4. Application of models for analysis of policies, where there are, for example, feedbacks to the economy from climatic change or CO2 control strategies, is just beginning.
From page 73...
... prevent any definitive statement today that excludes nonfossil fuel sources. With respect to the oceans, it now appears to be quite possible to measure the changing CO2 properties of the ocean over time by using modern techniques, though no ongoing program yet exists to do so.
From page 74...
... Special attention should be given to the role of the oceans and clouds, model comparison and validation, extremes, and non-CO2 greenhouse gases. The heat capacity of the upper ocean is potentially great enough to delay by decades the response of climate to increasing atmospheric CO2, as modeled without it; and the lagging ocean thermal response may cause important regional differences in climatic response to increasing CO2.
From page 75...
... Particular attention should be paid to improving estimates of mixing time scales in the main thermocline. Cloud amounts, heights, optical properties, and structure may be influenced by (^-induced climatic changes.
From page 76...
... Given the inertia created by the ocean thermal capacity and the level of natural fluctuations, we expect that achieving statistical confirmation of the C02-induced contribution to global temperature changes so as to narrow substantially the range of acceptable model estimates may require an extended period. Improvements in climatic monitoring and modeling and in our historic data bases for changes in CO2, solar radiance, atmospheric turbidity, and other factors may, however, make it possible to account for climatic effects with less uncertainty and thus to detect a CO2 signal at an earlier time and with greater confidence.
From page 77...
... "Greenhouse" gases Stratospheric temperatures other than C02 Radiation fluxes at the top Stratospheric and of the atmosphere tropospheric ozone Precipitable water content (and clouds) Snow and sea-ice covers Polar ice-sheet mass balance Sea level
From page 78...
... Once we become convinced that climate changes are indeed under way, we will seek to predict their future evolution with increasing urgency and with increasing emphasis on parameters of societal importance (e.g., sea level and rainfall)
From page 79...
... l.5.6.7.3 Agriculture Basic research on agriculture in relation to C02 assessment falls into two broad categories: (l) effects of CO2 on photosynthesis and plant growth and (2)
From page 80...
... l.5.6.7.5 Water Resources There is need to develop further the conceptual basis of analysis for all river basins; but the relationships between climate and water resources are complex and unique to each river basin, so that basin-bybasin studies are also needed. Priority should be given to regions with large commitments to irrigated agriculture and for basins where scanty or overabundant flow is already a problem.
From page 81...
... . The West Antarctic Ice Sheet: diagnosis and prognosis.
From page 82...
... . Response of the global climate to changes in atmospheric composition due to fossil fuel burning.
From page 83...
... . Climatic change as a mathematical problem.
From page 84...
... . West Antarctic Ice Sheet and C02 greenhouse effect: a threat of disaster.
From page 85...
... . Current climatic changes in the northern hemispere.
From page 86...
... . Report of the Meeting of Experts on Potential Climatic Effects of Ozone and Other Minor Trace Gases.


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