Planetary macro-engineering using orbiting solar reflectors

The prospect of engineering a planetary climate raises a multitude of issues associated with climatology, engineering on truly macroscopic scales and indeed the ethics of such ventures. Depending on personal views, such large-scale engineering is either an obvious necessity for the deep future, or yet another example of human conceit. In this chapter a simple climate model will be used to assess the possibility of engineering the Earth's climate (geo-engineering) using large orbiting reflectors. Two particular cases will be considered: active cooling of the climate to mitigate against anthropogenic climate change due to a doubling of the carbon dioxide concentration in the Earth's atmosphere and active heating of the climate to mitigate against an advance of the polar ice sheets of a magnitude comparable to that induced by the Milankovitch cycles. These two cases will be used as representative scenarios to allow the scale of the engineering challenge to be determined. In addition, even more visionary applications of solar reflectors to slowly manipulate the Earth's orbit will be investigated. While, engineering on such scales appears formidable at present, emerging capabilities to process lunar and asteroid material will allow such ventures to be considered in the future. This chapter aims to provide a foretaste of such future possibilities