Clouds & Climate Change: Preface

The color photograph of the full Earth taken by astronauts on their way to the moon ushered in a new age. Looking at Earth from space, we cannot see our political boundaries. Nor can we usually see the effects of our own activities.

What was and is striking about the image of the Earth from space is its exquisite and delicate beauty: the patterns of white clouds against the deep blue of the oceans. These patterns alter from moment to moment, from day to day, from season to season. They are probably quite different now than they were a billion or 4 billion years ago. Despite the fact that cloud patterns, amounts, and thicknesses change, the world’s climate has remained remarkably constant, and no doubt clouds play an important role in determining and regulating that climate. Defining the role of clouds in climate is one of the trickiest problems for scientists developing computer models of climate. (The modelers might dearly love to have the clouds go away!) It is also essential to determining whether and how human activities are upsetting the Earth’s delicate balance. To perceive, for example, how pollution may be affecting clouds, we must understand what a cloud is and what forces may shape or alter it.

These are questions that this module addresses. It introduces the basic features and classifications of clouds and cloud cover, and explains how clouds form, what they are made of, what roles they play in determining climate, and how they both cause and are affected by climate changes.