title: Geoengineering the climate: an overview and update.
abstract: The climate change that we are experiencing now is caused by an increase in greenhouse gases due to human activities, including burning fossil fuels, agriculture and deforestation. There is now widespread belief that a global warming of greater than 2(°)C above pre-industrial levels would be dangerous and should therefore be avoided. However, despite growing concerns over climate change and numerous international attempts to agree on reductions of global CO(2) emissions, these have continued to climb. This has led some commentators to suggest more radical 'geoengineering' alternatives to conventional mitigation by reductions in CO(2) emissions. Geoengineering is deliberate intervention in the climate system to counteract man-made global warming. There are two main classes of geoengineering: direct carbon dioxide removal and solar radiation management that aims to cool the planet by reflecting more sunlight back to space. The findings of the review of geoengineering carried out by the UK Royal Society in 2009 are summarized here, including the climate effects, costs, risks and research and governance needs for various approaches. The possible role of geoengineering in a portfolio of responses to climate change is discussed, and various recent initiatives to establish good governance of research activity are reviewed. Key findings include the following.- Geoengineering is not a magic bullet and not an alternative to emissions reductions.  - Cutting global greenhouse gas emissions must remain our highest priority. (i) But this is proving to be difficult, and geoengineering may be useful to support it.  - Geoengineering is very likely to be technically possible. (i) However, there are major uncertainties and potential risks concerning effectiveness, costs and social and environmental impacts.  - Much more research is needed, as well as public engagement and a system of regulation (for both deployment and for possible large-scale field tests).  - The acceptability of geoengineering will be determined as much by social, legal and political issues as by scientific and technical factors. Some methods of both types would involve release of materials to the environment, either to the atmosphere or to the oceans, in areas beyond national jurisdiction. The intended impacts on climate would in any case affect many or all countries, possibly to a variable extent. There are therefore inherent international implications for deployment of such geoengineering methods (and possibly also for some forms of research), which need early and collaborative consideration, before any deployment or large-scale experiments could be undertaken responsibly.
authors.affiliation: School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, European Way, Southampton SO14 3ZH, UK. j.g.shepherd@noc.soton.ac.uk
authors.forename: J G
authors.initials: JG
authors.lastname: Shepherd