Geoengineering – deliberately modifying the Earth’s environment to reverse climate change – is increasingly being proposed as a bridge to a carbon-neutral future. In June of 2008 the national science academies of the G8+5 nations (Brazil, Britain, Canada, China, France, Germany, India, Italy, Japan, Mexico, Russia, South Africa, and the United States) released a joint statement that included a specific call for research on the potential of geoengineering technologies to help stabilize the Earth’s climate (http://www.nationalacademies.org/includes/climatechangestatement.pdf). The possibility that geoengineering will be applied to combat global warming raises a host of environmental questions. Will such approaches actually work? Who will control the thermostat for the Earth? What other environmental consequences might arise and where would the effects be the greatest? We propose to hold a symposium that examines these and other issues, linking closely to the overall theme of the 2009 Annual Meeting: Ecological Knowledge and a Global Sustainable Society.