Geoengineering, the large-scale technological control of climate processes in order to offset anthropogenic global warming, is at this stage merely a prospective technology, yet it is already a controversial one. The idea of attempting to bring about deliberate large-scale changes in a complex, dynamic, chaotic system such as the atmosphere is highly ambitious. Like rDNA biotechnology and other new and emerging technologies before it, it is likely to provoke objections from opponents which are religious or implicitly religious in nature; for example, that it is “playing God” – overstepping the proper and safe limits of human freedom and control.