Policy Implications of Greenhouse Warming Mitigation, Adaptation, and the Science Base (1992) / Chapter Skim
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3 The Greenhouse Gases and Their Effects
3 The Greenhouse Gases and Their Effects
Pages 12-28
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From page 12... ...
Indirect evidence from tree rings, air bubbles trapped in glacial ice as it formed, and other sources has been used to reconstruct past concentrations of these gases. The dispersion and transformation of greenhouse gases in the atmosphere are also fairly well understood.
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From page 13... ...
CFor each gas in the table, except CO2, the "lifetime" is defined as the ratio of the atmospheric concentration to the total rate of removal. This time scale also characterizes the rate of adjustment of the atmospheric concentrations if the emission rates are changed abruptly.
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From page 14... ...
EARTH'S RADIATION BALANCE The climatic system of the earth is driven by radiant energy from the sun. Incoming solar radiation at the top of the earth's atmosphere has an average intensity, over the year and over the globe, of 340 W/m2.
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From page 15... ...
FIGURE 3.2 Additional radiative forcing of principal greenhouse gases from 1990 to 2030 for different emission rates. The horizontal axis shows changes in greenhouse gas emissions ranging from completely eliminating emissions (-100 percent)
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From page 16... ...
, 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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From page 17... ...
list of possible changes in characterizing features just mentioned imply that increases in greenhouse gas concentrations will lead to modifications of the climate. surface plus 104 percent upward radiation balanced by 50 percent of incoming solar continuing to the earth's surface, 70 percent outgoing radiation, and 88 percent downward radiation)
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From page 18... ...
Scenarios of changes in committed future warming accompanying different greenhouse gas emission rates can be constructed by repeating this process for given emission rates and adding up the results. SOURCE: Courtesy of Michael C
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From page 19... ...
The scale labeled 5°C is associated with the hypothesis that the equivalent of doubling CO2 would produce a 5° increase in the equilibrium global average temperature, and the 1°C scale accompanies the hypothesis that such a doubling would imply a 1° increase. Figure 3.4 can be used to construct scenarios of changes in committed future warming resulting from policies that lead to different greenhouse gas emission rates.
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From page 20... ...
This is especially so given that the expected global temperature rise is smaller than current naturally occurring regional temperature fluctuations on all time scales, daily, seasonal, and decadal. General circulation models most commonly simulate the equilibrium climatic conditions associated with doubling atmospheric concentrations of CO2 compared to preindustrial levels.
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From page 21... ...
Simply looking at the global average temperature associated with an equivalent doubling of preindustrial levels of CO2 does not convey some important aspects of climate change. For example, there is no particular significance to exactly that level of greenhouse gas concentrations.
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From page 22... ...
In particular, it is not possible to determine how much, if any, of the average global temperature rise over the last century might be attributed to greenhouse warming. Increasing atmospheric concentrations of greenhouse gases may produce changes in both the magnitude and the rate of change of global average temperature that have few or no precedents in the earth's recent history.
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From page 23... ...
Southern Hemisphere (c) Global Average 1870 1890 1910 1930 YEAR 1950 1970 1990 FIGURE 3.5 Combined land air and sea surface temperature relative to 1951-1980 average temperatures.
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From page 24... ...
The top panel shows the last million years, the second panel amplifies the last 100,000 years, the third panel the last 10,000 years, and the bottom panel the last 1,000 years. The horizontal line at 15°C is included for reference and is the approximate average global temperature for the period 1951 to 1980.
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From page 25... ...
Some have suggested that global warming due to increased atmospheric concentrations of greenhouse gases could lead to disintegration of the West Antarctic Ice Sheet, most of which is grounded below sea level. If climate warms and warmer ocean water intrudes under the ice sheet, the release of ice from the sheet would accelerate.
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From page 26... ...
No credible claim can be made that any of these events is imminent: nonetheless, with continuing greenhouse gas accumulations, none of them are precluded. CONCLUSIONS Neither the available climate record nor the limited capabilities of the climate models permit a reliable forecast of the implications of continued
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From page 27... ...
2. The sensitivity of the climatic system to greenhouse gases is such that the equivalent of doubling CO2 could ultimately increase the average global temperature by somewhere between 1° and 5°C (1.8° and 9°F)
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From page 28... ...
The resulting transient period, or "lag," means that the global average surface temperature at any time is lower than the temperature that would prevail after all the redistribution had been completed. At the time of equivalent CO2 doubling, for example, the global average surface temperature may be as little as onehalf the ultimate equilibrium temperature associated with those concentrat~ons.
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