Policy Implications of Greenhouse Warming (1991) / Chapter Skim
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A QUESTIONS AND ANSWERS ABOUT GREENHOUSE WARMING
A QUESTIONS AND ANSWERS ABOUT GREENHOUSE WARMING
Pages 85-113
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From page 85... ...
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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From page 86... ...
APPENDIX A Reflected (25%) Incident Solar Radiation (100%)
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From page 87... ...
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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From page 88... ...
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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From page 89... ...
Yes. Figure A.2 shows projected changes in radiative forcing for different greenhouse gases between now and 2030.
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From page 90... ...
Am N2O like _ _ _ ,~ -- - Other Ch~orocarbons -1 00 -50 O 50 100 CHANGE IN ANTHROPOGENIC EMISSIONS FROM 1 990 TO 2030 (percent) FIGURE A.2 Additional radiative forcing of principal greenhouse gases from 1990 to 2030 for different emission rates.
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From page 91... ...
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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From page 92... ...
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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From page 93... ...
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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From page 94... ...
What are the major "unknowns" in predictions? Major uncertainties include: · Future emissions of greenhouse gases · Role of the oceans and biosphere in uptake of heat and CO2 Amount of CO2 and carbon in the atmosphere, oceans, biota, and soils Effectiveness of sinks for CO and other greenhouse gases, especially 2 CH · Interactions between temperature change and cloud formation and the resulting feedbacks feedbacks Effects of global warming on biological sources of greenhouse gases Interactions between changing climate and ice cover and the resulting Amount and regional distribution of precipitation Other factors, like variation in solar radiation 18.
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From page 95... ...
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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From page 96... ...
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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From page 97... ...
, ,[ , 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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From page 98... ...
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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From page 99... ...
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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From page 100... ...
forestry and fishery GNP 17 billion Natural Preserve a large mammal in zoo 1500-3000 year landscaper 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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From page 101... ...
hThe cost of raising an offshore drilling platform 1 m is less than 1 percent of its total cost. Strengthening coastal properties for 100-mph wind would cost between a tenth and a third of current state and local service budgets for the entire United States.
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From page 102... ...
The Antarctic and Greenland ice sheets combined make up the world's largest reservoir of fresh water. The West Antarctic Ice Sheet alone contains enough water to raise global average sea level about 7 meters (23 feet)
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From page 103... ...
PREVENTING OR REDUCING ADDITIONAL GREENHOUSE WARMING 32. What are the sources of greenhouse gas emissions?
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From page 104... ...
TOTAL 32,880(100) aCO2-equivalent emissions are calculated from the Greenhouse Gas Emissions column by using the following multipliers: co2 CH4 CFC-ll and-12 N2O Numbers in parentheses are percentages of total.
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From page 105... ...
The panel ranks options for reducing greenhouse gas emissions or removing greenhouse gases from the atmosphere according to their cost-effectiveness. Some of these options have net savings or very low net implementation costs compared to other investments.
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From page 106... ...
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 millions ., 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. CThis depends on the actual implementation level and is controversial.
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From page 107... ...
CO2 equivalent emissions 0 2 4 6 8 EMISSION REDUCTION (billion tons CO2 equivalent per year) FIGURE A.4 Comparison of mitigation options.
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From page 108... ...
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. Other systems are sensitive to climatic changes but can be adapted at a cost whose present value is small in comparison to the overall level of economic activity.
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From page 109... ...
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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From page 110... ...
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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From page 111... ...
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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From page 112... ...
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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From page 113... ...
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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