Al Qaeda detonates a nuclear weapon in Times Square during rush hour, wiping out half of Manhattan and killing 500,000 people. A virulent strain of bird flu jumps to humans in Thailand, sweeps across Asia, and claims more than fifty million lives. A single freight car of chlorine derails on the outskirts of Los Angeles, spilling its contents and killing seven million. An asteroid ten kilometers wide slams into the Atlantic Ocean, unleashing a tsunami that renders life on the planet as we know it extinct. Social science. Large print. Risk assessment.