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1.0 Introduction

Weather and climate have had major impacts on people and civilization as long as humanity has existed on this planet. The effects of weather on the earliest primitive societies were local and relatively direct; temperature and precipitation variations affected comfort, hunting, and agriculture, while severe storms undoubtedly caused life and property losses. Climate variations, however, affected whole civilizations, stimulating mass migrations of societies as shifting climate patterns made them leave their homes to seek more hospitable surroundings.

One might think that recent improvements in technology have made modern societies less vulnerable to severe weather and variations in climate. But just the opposite is true. The importance of weather and climate has never been greater in the United States and the world. Rapidly increasing populations and the complexities of national and world economies have made societies more sensitive and more vulnerable to disruptions caused by weather phenomena such as flash floods, blizzards, severe storms, and hurricanes; and to climate variations such as droughts, excessive rainfall, and temperature extremes. The climatic changes anticipated in the next few decades are unprecedented in modern experience. To a society fixed by national boundaries and constrained by an intricate economic system based on presumptions of constancy, these changes will be of major proportions.

1.1 Present Sensitivities to Weather and Climate

A few examples illustrate the nation's high sensitivity to weather and climate:

• The safety and efficiency of our air transportation system are adversely affected by weather. Over 250 lives were lost in commercial airline crashes at New Orleans and Dallas as a result of wind shear "microbursts" associated with severe thunderstorms. Although technology has made individual aircraft less susceptible to adverse weather, the air transportation system, with its interdependent components, is overstressed and increasingly weather sensitive. Two-thirds of all flight delays and over half of all aviation fatalities are weather related.