"As a participant in several international agreements on climate change, the United States has joined with other nations to express concern about climate change. However, at the national level the United States has not yet developed a comprehensive climate change policy. In the absence of a comprehensive policy direction, technological advances are creating alternatives to the traditional approaches to climate change (mitigation and adaptation). If deployed, these new technologies could modify the Earth's climate on a large scale. Moreover, these new technologies may become available to foreign governments and entities in the private sector to use unilaterally--without authorization from the United States government or an international treaty. The term 'geoengineering' describes this array of technologies that aim, through large-scale and deliberate modifications of the Earth's energy balance, to reduce temperatures and counteract anthropogenic climate change. Most of these technologies are at the conceptual and research stages, and their effectiveness at reducing global temperatures has yet to be proven. Moreover, very few studies have been published that document the cost, environmental effects, sociopolitical impacts, and legal implications of geoengineering. If geoengineering technologies were to be deployed, they are expected to have the potential to cause significant transboundary effects. In general, geoengineering technologies are categorized as either a carbon dioxide removal (CDR) method or a solar radiation management (SRM) method. CDR methods address the warming effects of greenhouse gases by removing carbon dioxide (CO2) from the atmosphere. CDR methods include ocean fertilization, and carbon capture and sequestration. SRM methods address climate change by increasing the reflectivity of the Earth's atmosphere or surface. Aerosol injection and space-based reflectors are examples of SRM methods. SRM methods do not remove greenhouse gases from the atmosphere, but can be deployed faster with relatively immediate global cooling results compared to CDR methods."
CRS Report for Congress, R41371