A talk Jamais Cascio gave at Hub Westminster in the Truth and Beauty event series. Jamais delivers by far the most powerful and frightening talk I've been to in years, considering not just the scientific and technical, but the political and military reality of geoengineering as a response to crises induced by global warming.
(Technical note: audio and video on this page is set up using HTML5+OGG. Firefox and Chrome handle this correctly. If you have to download the .ogg files to view/listen, use VLC. All tools are cross-platform and FOSS.)