It would be rash to conclude that, on balance, the environment of the globe as a whole is either deteriorating or improving, or that the survival of the societies we know depends upon filling a simple set of prescriptions. It is all too complex and dynamic, whether it involves managing greenhouse gases or Nile snails... The future condition of the globe's interlocking natural and social systems depends more on human behavior than on the further investigation of natural processes, however desirable that may be.