ABSTRACT
We live in a time of renewed perception of climatic and environmental change. For many people this arises from fears about the possibility that mans activities, and their increasing scale and variety, may have side-effects that disturb the climatic regime, just as they are visibly changing other aspects of the environment about us. Others may be interested in the possibility of using the increasing power of our technology deliberately to modify the climate: for instance, to increase the total cultivable area of the world or, sad to say, to change the pattern of climate as a possible strategy of war. In any case, many people now know that there have been significant shifts of climate during the twentieth century: at first, a more or less global warming to about 1950, then some cooling. More recently, a notable increase in the incidence of extremes of various kinds in almost all parts of the world has hit agriculture and created difficulties for planning in many fields.
