Policy Implications of Greenhouse Warming (1991) / Chapter Skim
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3 THE GREENHOUSE GASES AND THEIR EFFECTS
3 THE GREENHOUSE GASES AND THEIR EFFECTS
Pages 10-26
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From page 10... ...
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 11... ...
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 12... ...
As can be seen in Figure 3.3, the incoming arrows, representing the incoming intensity
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From page 13... ...
< _ -~ ~ Other Chlorocarbons -100 -50 O 50 100 CHANGE IN ANTHROPOGENIC EMISSIONS FROM 1990 TO 2030 (percent) 13 FIGURE 3.2 Additional radiative forcing of principal greenhouse gases from 1990 to 2030 for different emission rates.
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From page 14... ...
POLICY IMPLICATIONS OF GREENHOUSE WARMING Reflected (25%) Incident Solar Radiation (100%)
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From page 15... ...
list of possible changes in characterizing features just mentioned imply that increases in greenhouse gas concentrations will lead to modifications of the climate. It is important to recognize that these climate modifications are not instantaneous responses to the gas concentration changes that produce them.
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From page 16... ...
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.
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From page 17... ...
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 18... ...
General circulation models most commonly simulate the equilibrium climatic conditions associated with doubling atmospheric concentrations of CO2 compared to preindustrial levels. Current GCM simulations based on these assumptions show a range of global average equilibrium temperature increases of 1.9° to 5.2°C (3.4° to 9.4°F)
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From page 19... ...
GCM simulations of other climate variables, such as precipitation, soil moisture, and northsouth energy transport, are much less satisfactory. They do not provide credible quantitative estimates of the longer-term changes in global climate that might be driven by greenhouse gas accumulations.
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From page 20... ...
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 21... ...
Southern Hemisphere (c) Global Average ~ ~R P Ll , , , , , I 1870 1890 1910 1930 YEAR 21 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 22... ...
The horizontal line at 15°C is included for reference and is the approximate average global temperature for the period 1951 to 1980. Considerable uncertainty attaches to the record in each panel, and the temperature records are derived from a variety of sources, for example, ice volume, as well as more direct data.
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From page 23... ...
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 24... ...
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 accumulations of greenhouse gases in the atmosphere.
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From page 25... ...
5. Current interpretations of temperature records reveal that the global average temperature has increased between 0.3° and 0.6°C (0.5° and 1.1°F)
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From page 26... ...
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 concentrations.
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