Here are two challenges that the world has had to face in 2008: 1) Construction of the Large Hadron Collider was recently completed. Experiments using this machine will yield new knowledge of a fundamental kind. There is also a theoretical risk, believed to be vanishingly small but not zero, that the machine could create a black hole capable of destroying the Earth. Should the machine be turned on? 2) Fertilizing “desert” regions of the oceans with iron is expected to stimulate phytoplankton growth, sucking carbon dioxide into the oceans and thus helping to mitigate climate change. It might also alter vital ocean ecosystems. To know the full consequences of ocean fertilization, large-scale experiments are needed. Should they be allowed?