Introduction

Abstract

The human sense of the passage of time is among the most intimate perceptions that we have of the external world. Our feeling for rates of change is as closely linked, if not more so, to our own activities as to events beyond our control. We form vivid memories of singular events such as droughts, floods, and hurricanes largely by reference to the stages of our own lives at the time of their occurrence and the daily routines they interrupt; but we are unaware or only dimly aware of processes operating at a much slower pace to produce change that is barely perceptible over the course of a human lifetime. Similar limitations characterize our perception of space. We cannot see beyond our local domain and so must rely on second-hand evidence to assess emerging global-scale concerns.