There is growing scientific evidence that humanity faces a number of threats that jeopardize its future. Public perceptions of these threats, both their risks and reactions to them, are important in determining how humanity confronts and addresses the threats. This study investigated the perceived probability of threats to humanity and different responses to them (nihilism, fundamentalism and activism), in four Western nations: the US, UK, Canada and Australia. Overall, a majority (54%) rated the risk of our way of life ending within the next 100 years at 50% or greater, and a quarter (24%) rated the risk of humans being wiped out at 50% or greater. The responses were relatively uniform across countries, age groups, gender and education level, although statistically significant differences exist. Almost 80% agreed "we need to transform our worldview and way of life if we are to create a better future for the world" (activism). About a half agreed that "the world's future looks grim so we have to focus on looking after ourselves and those we love" (nihilism), and over a third that "we are facing a final conflict between good and evil in the world" (fundamentalism). The findings offer insight into the willingness of humanity to respond to the challenges identified by scientists and warrant increased consideration in scientific and political debate.