Atmospheric carbon dioxide concentration has increased globally from about 280 ppm before the Industrial Revolution (Pearman 1988) to about 353 ppm in 1990. That increase, and the continuing increase at a rate of about 1.5 ppm per annum, owing mainly to fossil fuel burning, is likely to cause change in climate, in primary productivity of terrestrial vegetation (managed and unmanaged), and in the degree of net sequestration of atmospheric CO into organic form. The quantitative role 2 of the latter in attenuating the increase in atmospheric CO concentration itself is 2 an important but uncertain element of the global carbon-cycle models that are required to predict future increases of atmospheric CO concentration. 2 In my experience in workshops and other multidisciplinary gatherings, argument arises in discussion of this topic among different groups of scientists such as bioclimatologists, plant physiologists, biogeochemists and ecologists. Plant concentration physiologists are often impressed by the positive effect of higher CO 2 on plant growth under experimental controlled environments and argue that this would be at least partly expressed in the field for many species and communities.

r-------------{ Environment (Disease) Fig. 1. A schematic presentation of the interplay between the external environment, pathogen and animal, which influences resistance to infectious disease. Disturbance in equilibrium results in infection and disease skin and the mucous membranes of the respiratory tract. These tissues are in contact with the environment, and direct injury to them facilitate entry of pathogenic microorganisms through these important natural barriers. Sunburn and frostbite are examples of such adverse effects. Climatic factors such as heat and cold may also act as physiological stress factors which affect the specific and non-specific responses of the body to infection. 1.1.2 Pathogen Survival Climatic factors may affect dispersal, spread and survival of pathogenic micro organisms in the environment. This is also true for arthropod vectors such as mosquitos and ticks (Smith 1970; Ferguson and Branagan 1972). The density of the animal population is an important factor determining the concentration of patho gens in the environment. Population density can be influenced by weather condi tions, as animals respond to heat and cold by typical changes in behaviour. For example, in cold weather they tend to huddle together. This behaviour results in increased population density, which in turn involves an increased risk of the spread of airborne infections.

This volume contains reviews on five different aspects of bioclimatology: (1) The establishment, maintenance and use of data from automatic weather station networks for agricultural purposes; (2) Techniques for estimating global and ultraviolet irradiance at the earth's surface, and the net radiation balance from operational satellite observations; (3) Mathematical models of the effects of climate on energy and mass balance in crop production; (4) Paleoecological and experimental studies of the response of stomatal density to changes in the atmospheric CO2 concentrations; and (5) The sensory and behavioral responses of insects and other invertebrates to small CO2 gradients resulting from plant and animal metabolism, considering the global changes in CO2 concentration and air temperature.

The economic costs of frosts in agriculture and horticulture in many parts of the world can be very significant. Reports in the media include accounts on how frosts have devastated coffee crops in Brazil or in Papua New Guinea, and how frosts have seriously damaged the Florida citrus industry. Frost may cause losses in current harvests or a decline in future yields through more permanent damage to trees and bushes. Damaging frosts may occur as infrequent, short-term events with sub-zero temperatures or with unusually severe winter temperatures which extend over long periods. In this book we have aimed at providing a comprehensive review of recent advances in the area of frost research. The stimulus for writing this book has come from the recognition that there is a shortage of recent texts which deal exclusively with the bioclimatology of frost. Bioclimatology deals with the relations between climate and life and the present text is particularly concerned with the effects of low temperatures on plants. Our purpose has been to assist researchers, engineers, extension officers and students in understanding the physical aspects of frost occurrence and frost distribution as well as the biological and phenological aspects of frost damage and to provide an overview of direct and indirect methods of frost pro tection and prevention.