Agriculture shares many of the characteristics and problems of manufacturing industry but it is peculiar in a number of ways. It is, and has always been, particularly vulnerable to changes in the local weather. Production is seriously curtailed in weather that differs from the mean significantly by being very cold, very wet and very hot and dry. These responses to the environment may be made worse by plant diseases and animal diseases, themselves sometimes responsive to climatic change. In the past the result has been famine and high prices. By contrast, especially favourable conditions can enhance plant yields and animal production and produce a surfeit of food with resulting glut and the collapse of prices. In the preceding section we have demonstrated how science has provided the farmer with a greater degree of control over these variables affecting his business so that year on year production of both plants and animals is more stable. This has allowed better planning and budgeting for the farming business.

A second characteristic of agriculture is that, because most countries are at least partly self-sufficient in staples, changes (even marginal ones) in the level of production from year to year result in great fluctuations in the price of world commodities and perturbation in the farmers' annual income which is largely outwith their control, with consequent severe social disruption.

In an effort to moderate these effects, which otherwise threaten to extinguish agricultural industries, governments have had recourse to various forms of protection and price support; the policies of British governments in our fifty-year period are outlined in Chapter 2.