Policy Implications of Greenhouse Warming Mitigation, Adaptation, and the Science Base (1992) / Chapter Skim
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A Questions and Answers About Greenhouse Warming
A Questions and Answers About Greenhouse Warming
Pages 663-691
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From page 663... ...
Rising atmospheric concentrations of CO2, CH4, and CFCs suggest the possibility of additional warming of the global climate. The panel refers to warming due to increased atmospheric concentrations of greenhouse gases as "greenhouse warming." Measurements of atmospheric CO2 show that the 1990 concentration of 353 parts per million by volume (ppmv)
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, and at the earth's surface, at 133 percent (45 percent absorbed solar radiation plus 88 percent downward radiation from the atmosphere balanced by 29 percent evaporation and mechanical heat transfer and 104 percent upward radiation)
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-CFCs do not occur naturally, and so they were not found in the atmosphere until production began a few decades ago. Continued increases in atmospheric concentrations of greenhouse gases would affect the earth's radiative balance and could cause a large amount of additional greenhouse warming.
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The overall contribution of greenhouse gases to global warming depends on their atmospheric lifetime as well as their ability to trap radiation. Table A.1 shows the relevant characteristics of the principal greenhouse gases.
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This time scale also characterizes the rate of adjustment of the atmospheric concentrations if the emission rates are changed abruptly. CO2 is a special case because it is merely circulated among various reservoirs (atmosphere, ocean, biota)
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FIGURE A.2 Additional radiative forcing of principal greenhouse gases * om 1990 to 2030 for different emission rates.
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It cannot be proven to a high degree of confidence that this warming is the result of the increased atmospheric concentrations of greenhouse gases. There may be an underlying increase or decrease in average temperature from other, as yet undetected, causes.
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1 °C 5°C _ 0.3 _ 1.5 _ 0.2 _ 0.1 1.0 0.5 0.0 -0.1 0.0 FIGURE A.3 Commitment to future warming. An incremental change in radiative forcing between 1990 and 2030 due to emissions of greenhouse gases implies a change in global average equilibrium temperature (see text)
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The oceans, covering roughly 70 percent of the earth's surface, absorb heat from the sun and redistribute it to the deep oceans slowly. It will be decades, perhaps centuries, before the oceans and the atmosphere fully redistribute the absorbed energy and the currently "committed" temperature rise is actually "realized." The temperature at which the system would ultimately come to rest given a particular level of greenhouse gas concentrations is called the "equilibrium temperature." Since atmospheric concentrations of greenhouse gases are constantly changing, the temperature measured at any time is the "transient" temperature, which lags behind the committed equilibrium warming.
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Interactions between temperature change and cloud formation and the resulting feedbacks · Effects of global warming on biological sources of greenhouse gases · Interactions between changing climate and ice cover and the resulting feedbacks · Amount and regional distribution of precipitation · Other factors, like variation in solar radiation 18. How can the uncertainties best be handled?
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It is possible only at great expense or by incurring risks not now understood, unless the earth is itself self-correcting. Continued increases in atmospheric concentrations of greenhouse gases would probably result in additional global warming.
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of change in the radiative forcing of the earth. It is useful to categorize the possible types of intervention into three types: Actions to eliminate or reduce emissions of greenhouse gases Actions to "offset" such emissions by removing such gases from the atmosphere, blocking solar radiation, or altering the earth's reflectivity or absorption of energy · Actions to help human and ecologic systems adjust to new climatic conditions and events In this study the panel analyzes the first two types of action together under the label of "mitigation," since they are aimed at avoiding or reducing greenhouse warming.
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Climatic changes associated with additional greenhouse warming are expected to emerge slowly enough that these industries may be expected to adjust as climate changes. Some industries, such as electric power production, have longer investment cycles, and might have more difficulty responding as quickly.
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Human societies exhibit a wide range of adaptive mechanisms in the face of changing climatic events and conditions. Projected climatic changes, especially at the upper end of the range, may overwhelm human adaptive mechanisms in areas of marginal productivity and in countries where traditional coping mechanisms have been disrupted.
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Some type of anticipation for meeting them may be justified. The category of extremely adverse impacts would be associated with high potential costs and would disrupt most aspects of the system in question.
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farm GNP 76 billion Forestry Prepare and plant 130 acre Treat with herbicide 41 acre Fertilize 36 acre Thin 55 acre Protect from fire for 1 year 1.36 acre 1983 fire protection on state and 245 million private forestse 1986 U.S. forestry and fishery GNP 17 billion Natural Preserve a large mammal in zoo 1500-3000 year landscaped Preserve a large bird in zoo 100-1000 year Preserve a plant in botanical garden 500 year Recover peregrine falcon 3 million 1970- 1990 Recover all endangered birds of prey 5 million year Preserve an acre in a large reserve 50-5000 acre 1985 expenditure on wildlife-related recreation, including hunting and fishing Budget National Park Service 55.4 billion 1 billion year
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Increasing expenditures on all forest land to $1.36 per acre would cost about $500 million or 3 percent of forest and fishery GNP. fThe cost of recovering all endangered birds of prey is 1 ten-thousandth and the cost of the National Park Service is 2 percent of the annual expenditures on wildlife-associated recreation.
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The West Antarctic Ice Sheet alone contains enough water to raise global average sea level about 7 meters (23 feet)
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PREVENTING OR REDUCING ADDITIONAL GREENHOUSE WARMING 32. What are the sources of greenhouse gas emissions?
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All entries are rounded because the exact values are controversial. aCO2-equivalent emissions are calculated from the Greenhouse Gas Emissions column by using the following multipliers: co2 CH4 CFC-11 and-12 N2O Numbers in parentheses are percentages of total.
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The so-called geoengineering options have the potential of substantially affecting atmospheric concentrations of greenhouse gases. They have the ability to screen incoming sunlight, stimulate uptake of CO2 by plants and animals in the oceans, or remove CO2 from the atmosphere.
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Net benefit 300 million Industrial energy management Net benefit to low cost 500 million Transportation system management Net benefit to low cost 50 million Power plant heat rate improvements Net benefit to low cost 50 million Landfill gas collection Low cost 200 million Halocarbon-CFC usage reduction Low cost 1400 million Agriculture Low cost 200 million Reforestation Low to moderate costs 200 million Electricity supply Low to moderate costs 1000 millione NOTE: Here and throughout this report, tons are metric. aNet benefit = cost less than or equal to zero Low cost = cost between $1` and $9 per ton of CO2 equivalent Moderate cost = cost between $10 and:$99 per ton of CO2 equivalent High cost = cost of $100 or more per ton of CO2 equivalent bThis "maximum feasible" potential emission reduction assumes 100 percent implementation of each option in reasonable applications and is an optimistic "upper bound" on emission reductions.
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CO2 equivalent emissions 4 6 EMISSION REDUCTION (billion tons CO2 equivalent per year) 8 FIGURE A.4 Comparison of mitigation options.
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The panel's analysis suggests that some human and natural systems are not very sensitive to the anticipated climatic changes. These include most sectors of industry.
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The appropriate level of expenditure depends on the value attached to the adverse outcomes compared to other allocations of available funds, human resources, and so on. In essence, the answer depends on the degree of risk aversion attached to adverse outcomes of climate change.
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Current scientific understanding of greenhouse warming is both incomplete and uncertain. Response depends in part on the degree of risk aversion attached to poorly understood, low-probability events with extremely adverse outcomes.
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In addition, there are possible extremely adverse consequences, such as changing ocean currents, that are poorly understood today. The response to such possibilities depends on the degree of risk aversion concerning those outcomes.
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Three areas dominate the panel's analysis of reducing or offsetting current emissions: eliminating CFC emissions and developing substitutes that minimize or eliminate greenhouse gas emissions, changing energy policy, and utilizing forest offsets. Eliminating CFC emissions has the biggest single contribution.
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Because the geoengineering options have the potential to affect greenhouse warming on a substantial scale, because there is convincing evidence that some of these cause or alter a variety of chemical reactions in the atmosphere, and because the climate system is poorly understood, such options must be considered extremely carefully. If greenhouse warming occurs, and the climate system turns out to be highly sensitive to radiative forcing, they may be needed.
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