Policy Implications of Greenhouse Warming Mitigation, Adaptation, and the Science Base (1992) / Chapter Skim
Currently Skimming:
28 Geoengineering
28 Geoengineering
Pages 433-464
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 433... ...
Most of these options have to do with the possibility of compensating for a rise in global temperature, caused by an increase in greenhouse gases, by reflecting or scattering back a fraction of the incoming sunlight. Other geoengineering possibilities include reforesting the United States to increase the storage of carbon in vegetation, stimulating an increase in oceanic biomass as a means of increasing the storage and natural sequestering of carbon in the ocean, decreasing CO2 by direct absorption, and decreasing atmospheric halocarbons by direct destruction.
|
From page 434... ...
There is also a need for more detailed design, development, and cost analysis of the proposed deployment systems, perhaps including experimentation with specific hardware for deployment. Such work would give much more information with which to decide whether such systems could be deployed at a reasonable cost, and whether they would be likely to work as suggested by the preliminary evaluations included below.
|
From page 435... ...
We can use the past and our understanding of the nature of the physics and chemistry to guide us in looking for new effects as natural events occur: the next significant volcanic eruption, for example, can be used as an opportunity to extend our understanding of the effects of dust, sulfuric acid aerosol, and chemicals produced by volcanic eruptions on stratospheric chemistry and the climate system. The possibility would have to be taken into account that a natural event occurring during a mitigation activity could push the system beyond its normal bounds.
|
From page 436... ...
Improving our understanding of these matters in this way may enable us to make rational decisions on what risks to take if we desire to use geoengineering or other means of mitigation to counter any greenhouse warming produced by greenhouse gas increases. Particular caution must be exercised because although changing atmospheric chemistry and changing global reflectivity may both have an impact on global mean temperature, the relevant physics for each is very different.
|
From page 437... ...
of carbon compared to the 750,000 Mt (750 petagrams) of carbon in the atmosphere (World Resources Institute, 19901.i Although it should be noted that the amount of carbon stored in the ocean and lithosphere is much larger than that in either the atmosphere or the land, the time scales over which they equilibrate with the atmosphere are very large.
|
From page 438... ...
TABLE 28.1 Total Planting and Seeding by Ownership Category in FY 1989 Acres Percent of All Planting Federal government National forests307,138 10.2 Department: of the Interior52,006 1.7 Other federal agencies9,257 0.3 TOTAL368,401 12.2 Nonfederal public State forests57,133 1.9 Other state agencies6,013 0.2 Other public agencies13,515 0.4 TOTAL76,661 2.5 Private Forest industries1,248,565 41.3 Other industry22,225 0.8 Nonindustrial owners1,306,096 43.2 TOTAL2,576,886 85.3 GRAND TOTAL3,021,948 100.0
|
From page 439... ...
Researchers have documented drastic improvements in the present net productivity (carbon uptake) of several species of trees.
|
From page 440... ...
Therefore a reforestation strategy for sequestering carbon might theoretically involve the use of fast-growing species with advanced silviculture techniques on optimal sites. However, there is a trade-off between maximum carbon storage and maximum rate of carbon uptake.
|
From page 441... ...
Policy Options Public policy decisions to increase carbon storage through reforestation involve such silviculture issues as replanting, selection of species to be planted, and land management practices such as fertilization. To implement these reforestation options, however, someone must pay for the reforestation itself and for the cost of maintaining land in forest cover.
|
From page 442... ...
This analysis recognizes the large land resource required and adopts a conservative approach with respect to the U.S. Forest Service analysis of the amount of carbon that might be sequestered.
|
From page 443... ...
Thus trace inputs from atmospheric dust events could trigger blooms of the plankton and ultimately lower atmospheric CO2. Finally, the ice core record shows that glacial times, with dry and dusty continents, are characterized by strong dust input to oceans.
|
From page 444... ...
The NRC workshop suggests that iron fertilization might remove an average of 1.8 Gt C/vr over a 100-Year period. ,, ~, The workshop suggests an application of 1 to 5 Mt Fe/yr in the form of a solution of ferrous chloride (FeCl2)
|
From page 445... ...
, for a total of $12 to $18 million per year. Ferrous chloride, mentioned by the NRC workshop, is much more expensive than ferrous sulfate.
|
From page 446... ...
, anaerobic decomposition of algae to CH4, and the possible formation of large amounts of haloforms and dimethyl sulfide. As noted in the discussion of cloud stimulation below, the natural organisms whose growth would be stimulated by the addition of iron might be expected to produce dimethyl sulfide, which would form cloud condensation nuclei.
|
From page 447... ...
The assumption that a 1 percent decrease in sunlight is equivalent to mitigating the greenhouse effect of 1000 Gt of carbon (or 4000 Gt CO:) is key for all of the estimates that follow.6 - ~ ^ ^ ~ Ramanathan's increase of 0.5 percent in planetary albedo quoted above as sufficient to halve the effect of a CO2 doubling is used here and below as a 1 percent screening effect for estimating purposes.
|
From page 448... ...
To minimize launch costs, very small dust particles are required. However, because of solar radiation pressure, small dust is driven out of orbit or into the earth's atmosphere in very short times; the particles are barely orbital (Mueller and Kessler, 1985~.
|
From page 449... ...
Mass Estimates Ramaswamy and Kiehl (1985) estimate that an aerosol dust loading of 0.2 g/m2 for dust with a radius of about 0.26 An increases the planetary albedo by 12 percent, resulting in a 15 percent decrease of solar flux reaching the surface.
|
From page 450... ...
One possible effect of this heating might be to change the atmospheric chemistry to augment or destroy stratospheric ozone. Additional stratospheric dust could provide additional surface area on which chlorine compounds could be adsorbed, thus possibly increasing the rate of destruction of stratospheric ozone.
|
From page 451... ...
Note that the dust can be expected to produce visible optical effects, such as spectacular sunsets, as in the case of volcanic dust. Delivery Scenarios Naval Rifles A 16-inch naval rifle fired vertically could put a shell weighing about 1 t up to an altitude of 20 km.
|
From page 452... ...
Uncertainty regarding clouds and the required dust density for a 1 percent effect on radiative forcing suggests that it is reasonable, and even conservative, to put these costs in the range $0.03 to $1.0/t CO2 mitigated. Rockets At the present time, the cost of sounding rocket launches (using available surplus rockets such as the Nike Orion, which cost about $25,000 and carry a payload of 500 pounds)
|
From page 453... ...
The comments made above about the possible effect of dust on stratospheric ozone apply as well to ozone in the low stratosphere, but not in the troposphere. The altitude of the tropopause varies with latitude and season of the year.
|
From page 454... ...
suggests that the average low-cloud reflectivity could be increased if the abundance of cloud condensation nuclei (CCN) increased due to emissions of SO2.
|
From page 455... ...
Mass Estimates of Cloud Condensation Nuclei With Albrecht's assumption in mind that cloudiness in a typical ocean region is limited by the small number of CCN, we now extrapolate to the entire globe. On the average, 31.2 percent of the globe is covered by marine stratiform clouds (Charlson et al., 19871.
|
From page 456... ...
rr~ Cost Estimates The primary cost of this process involves the mechanism for distributing SO2 in the atmosphere at the correct location. Assume a fleet of ships, each carrying sulfur and a suitable incinerator.
|
From page 457... ...
ATMOSPHERIC CHLOROFLUOROCARBON REMOVAL Another option for mitigating greenhouse warming could be to remove chlorofluorocarbons (CFCs) from their principal reservoir, the lower atmosphere or troposphere.
|
From page 458... ...
CONCLUSIONS Several of the geoengineering possibilities discussed in this chapter, including atmospheric CFC removal, space mirrors, and the multiple balloon stratospheric screen, appear, with current technology or that expected to be available soon, to be either impractical, too cumbersome to manage, or too expensive. These ideas might merit some further study to be certain of this conclusion but do not now seem worth great effort.
|
From page 459... ...
Cloud stimulation by provision of cloud condensation nuclei appears to be a feasible and low-cost option capable of being used to mitigate any quantity of CO2 equivalent per year. Details of the cloud physics, verification of the amount of CCN to be added for a particular degree of mitigation, and the possible acid rain or other effects of adding CCN over the oceans need to be investigated before such a system is put to use.
|
From page 460... ...
It will be important to observe the effects on stratospheric chemistry of any volcanic eruptions that occur, with special attention to separating the effects of dust, aerosol, and hydrochloric acid. Of these systems to alter the planetary albedo, the increase of low-level marine clouds by increasing CON and the delivery of dust to the stratosphere by using large rifles seem the most promising.
|
From page 461... ...
, one can make a crude estimate of the mass of lower stratospheric dust by noting that they give the density at 20 km as about 1 ma/ m3. The "all sizes" curve in their Figure 9 suggests a reasonably constant concentration in the 8 km from 12 to 20 km.
|
From page 462... ...
1976. The global scale dispersion of the eruption clouds from major volcanic eruptions.
|
From page 463... ...
1990. Costs of Sequestering Carbon Through Tree Planting and Forest Management in the United States.
|
From page 464... ...
Report GMR-2820. Warren, Mich.: General Motors Research Laboratories, and paper presented at the Conference on the Parameterization of Extended Clouds and Radiation for Climate Models, sponsored by the International Council of Scientific Unions and organized by the Joint Organizing Council of the Global Atmospheric Research Program of the United Nations, Oxford, England, September 1978.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.