Advanced noncarbon technologies, such as nuclear fission or fusion, space solar power, and geoengineering, could potentially play an important role in climate stabilization. Several of these technologies are controversial, in early stages of development, or both. Until an option can be shown not to be viable, however, we should work to understand the option's potential benefits and drawbacks.
Nuclear fission is an existing technology that could help stabilize climate. In some countries (e.g., France) nuclear power generates a substantial fraction of electricity, thus displacing CO2 emissions that might otherwise occur. Fission involves generating electricity by splitting heavy atomic nuclei, most commonly U235, into lighter atomic nuclei. Present nuclear reactor technology provides CO2-free electricity while posing unresolved problems of waste disposal and nuclear weapons proliferation. The supply of fissile material, which depends on price, can be extended greatly through the use of breeder reactors; however, such reactors could greatly exacerbate nuclear weapons proliferation. Fission can potentially play a large role in providing carbon-free energy, if the issues of safety, waste disposal, weapons proliferation, resource availability, and public acceptance can be adequately addressed.
Fusion involves generating electricity through the joining or fusing of light atomic nuclei to form heavier atomic nuclei. Fusion power holds the promise of a nearly inexhaustible source of climate-neutral energy. It is unlikely, however, that fusion power will be commercially available in the time frame needed to stabilize climate (Hoffert et al. 2002), although it may play a role in maintaining climate stability in future centuries.
Solar power satellites could be constructed to generate power in Earth orbit or on the moon and beam that power to the Earth (Hoffert et al. 2002). Advantages of the space environment include higher and more consistent solar fluxes (avoidance of clouds, day-night cycle, etc.). Currently, however, launch costs make this approach uneconomical. In general, space power options require very large scales before economies of scale can be realized. Furthermore, there are environmental and public health concerns.
Public resistance to beaming energy through the atmosphere to Earth's surface is likely. Space power will probably not be economically feasible during this century.
It has been suggested that climate change induced by anthropogenic CO2 could be cost-effectively counteracted with geoengineering schemes designed to diminish the solar radiation incident on, or absorbed by, Earth's surface. Several schemes have been proposed; these schemes typically involve placing reflectors or other light scatterers in the stratosphere or in orbit between the Earth and Sun, diminishing the amount of solar radiation incident on the Earth (Keith 2000; Govindasamy and Caldeira 2000). Less exotic, biosphere-based geoengineering approaches are possible, although they may be impractical or expensive or have other undesirable consequences. For example, the albedo of large-scale forests could be increased through selective logging. Changing C4 grasses to C3 grasses could partition more available energy into latent heat rather than sensible heat, thus cooling the planetary surface.
There are serious ethical, environmental, legal, technical, and political concerns associated with intentional climate modification. For example, political tensions could be heightened if countries were to undertake geoengineering efforts without first obtaining international consensus. It has been suggested that geoengineering should be researched as an emergency backup strategy in case we needed to head off a truly threatening climate change catastrophe (e.g., runaway methane hydrate degassing [see Gruber et al., Chapter 3, this volume]). Any geoengineering scheme is likely to have negative consequences, which would need to be carefully studied before any serious consideration of deployment.
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