A recent article from the University of Pittsburgh’s Centre for Biosecurity, Reducing the Risk of Human Extinction.
Abstract: In this century a number of events could extinguish humanity. The probability of these events may be very low, but the expected value of preventing them could be high, as it represents the value of all future human lives. We review the challenges to studying human extinction risks and, by way of example, estimate the cost effectiveness of preventing extinction-level asteroid impacts.
via Schneier