134 OUR COMMON JOURNEY

The previous chapter examined past trends and ongoing transitionsthat will need to be confronted in efforts to navigate a transitiontoward sustainability. This chapter looks to the future. We recog-nize that much of the continuing interaction between human develop-ment and the environment will be a process of “muddling through. ” The inevitable trial-and-error of selecting a course, learning, and correction will be carried out less by efforts to think through our futures than by the necessity of acting them out. The decisive factor in determining how effective, fair, and efficient this muddling will be is in our choices not of analytic tools, but rather of the social institutions that help to provide the incentives and feedbacks necessary for social learning. We nonetheless believe that the inevitable trials may be made more productive, and the likelihood of costly and irreversible errors may be reduced through orga-nized efforts to assess the possible future implications of present trends, relying on growing understanding of earth system processes and social goals. The international efforts in recent years to address threats to the stratospheric ozone layer is a case in point. Understanding as much as possible about what the future may hold is important. It can identify things societies should try to avoid. It can give useful insights about what societies should do now to prepare for plausible contingencies. It can even help societies to learn what they ought to want for the future, by helping to illuminate the alternatives before them, and some of the impli-cations of trying to achieve alternative futures. In some respects, the future is known. Using the laws of physics, th