Appearing during the first three hours, Prof. Peter Ward, the author of Under a Green Sky, discussed his latest work on hydrogen sulfide extinctions, and how we are creating the circumstances for extinctions in the future. His research has connected past mass extinctions and global warming. Greenhouse gases and the melting of the ice-caps could create a dangerous situation where the ocean currents stop circulating. The stagnation of the oceans' waters would lead to the thriving of a type of bacteria that produces hydrogen sulfide. Killing off life in the ocean and sending toxic gases into the atmosphere, hydrogen sulfide could actually turn the sky green, he noted.
The coast off of Namibia is a hydrogen sulfide "hot spot" and the eruptions can be seen in this NASA satellite photo. Curiously, it has been found that hydrogen sulfide can have startling medical benefits, putting injured people into a kind of suspended animation until they can be treated. For more on hydrogen sulfide, see this Wired interview with Ward.
He also talked about how the melting of ice and subsequent rise of sea levels will flood coastal cities. There'll be enormous costs associated with moving cities and infrastructure to inland locations, and the influx of saltwater could wipe out agriculture, he warned.