Global Catastrophic Risks (forthcoming, OUP, June 2008), edited by Nick Bostrom and Milan Cirkovic, with a foreword by Sir Martin Rees.

"To the (incomplete) extent that true risk levels are reflected in actuarial statistics, the world is a safer place than it has ever been: world life expectancy is now 64 years, up from 50 in the early twentieth century, 33 in Medieval Britain, and an estimated 18 years during the Bronze Age. Furthermore, technology and complex social organizations offer many important tools for managing the remaining risks.
Nevertheless, it is important to recognize that the biggest global catastrophic risks we face today are not purely external; they are, instead, tightly wound up with the direct and indirect, the foreseen and unforeseen, consequences of our own actions”.
From the introductory chapter of Global Catastrophic Risks (forthcoming, OUP, 2008). The whole of this chapter is available free for download below