A World of Weather, Edition 3: Chapter 17 Introduction

CHAPTER 17

THE HUMAN IMPACT ON WEATHER AND CLIMATE Weighing no more than a few grams, a single leaf rests serenely upon a frozen, snow-covered pond (see Color Plate 2.A). The darker leaf absorbs more solar radiation per unit area than the surrounding snow. The resulting increase in the leaf's temperature causes some snow in its immediate vicinity to melt. The leaf's influence on its surroundings demonstrates that even the most seemingly trivial and inconspicuous cog in nature can alter its environment.

Is it any wonder, then, that the human population, approximately 6.1 billion strong as of 2001 and growing at the rate of about 1.2% per year, exerts an increasingly significant impact on its environment - the entire planet? Human population has experienced an unprecedented explosion in the last 200 years. Consider that the world's population did not reach one billion until around 1800, but the second billion was added by 1925, and the third by 1959. Human population is forecast to swell to approximately nine billion by the year 2050. With this rapidly growing population comes an increasing anthropogenic, or human-induced, impact on our planet's weather and climate.

Figure 17.1a is a nighttime composite visible image of the earth from space, while Figure 17.1b is a close-up of the United States. On a global scale, the continents are outlined by the lights of cities as well as by fires ablaze at the ground. These lights, whether natural or artificial, are powered predominantly by the burning of carbon-rich natural resources such as coal, oil, and wood. In the process, gases and particles enter the atmosphere, changing the air's composition and radiative properties. At the same time, earth's surface is being altered, modifying the natural exchanges of energy (and mass, such as water) between ground and air.

In many ways, the old saying that "everybody talks about the weather but nobody does anything about it" is no longer valid. Although we cannot yet disarm a tornado or energize a particular cumulus cloud to produce rain on a specific plot of parched ground, we are, sometimes unintentionally, altering the environment. The discharge of a smokestack contributing to the formation of fog (see Color Plate 17.A) is an unmistakable example of this human imprint on the atmosphere, while the soot-stained snow around the Siberian industrial city of Troisk, seen in Figure 17.2, clearly illustrates our footprint on the earth's surface. In this chapter, we explore the reaches of this human impact on weather and climate, considering global, regional, and local effects. In the process, we will travel from the tropical rain forests of the Amazon to the brutal cold of the stratosphere high above Antarctica.