Many of the chapters of this book have looked at the rate of past environmental change, and at potential rates of change-or more likely at potential rates of changes in the rates of change-of the environment in the short-and mediumterm future. Many have also looked at how some rates of change-for example plant migration-can or cannot keep up with, for example, changes in climate. Some have also looked at the rates of change in societies which have been confronted by problems of climatic change. In Chapter 3 there is considerable discussion of the failure of the Vikings in Greenland to adapt to what for them appeared to be worsening climatic conditions, although other cultures survived in even ‘worse’ circumstances. What such studies suggest is that there is no way in which we can talk meaningfully of a rate of environmental change without talking about its impact on something else. From the perspective of human society it is the direct and indirect impacts on society that matter most in determining what is a critical rate of change-a point which Max Wallis also heavily underscores.