It is now widely recognized that human activities are transforming the global environment. In the time it has taken for this book to come to fruition and be published, the evidence for climate change and its disruption of societal activities has become stronger. In the first 11 months of 1998, there were major floods in China and Peru, enormous damage from Hurricane Mitch in Central America, record-breaking heat waves in Texas, and extensive drought and fires in Indonesia; weather-related property losses were estimated at over $89 billion, tens of thousands of lives were lost, and hundreds of thousands of people were displaced. This greatly exceeds damage estimates for any other year. The environment was ravaged in many parts of the globe. Many of these losses were caused by weird weather associated with the biggest El Niņo on record in 1997-98, and they were probably exacerbated by global warming: the human-induced climate change arising from increasing carbon dioxide and other heat-trapping gasses in the atmosphere. The climate is changing, and human activities are now part of the cause. But how does a climate change manifest itself in day-to-day weather?
This book approaches the topic by explaining distinctions between weather and climate and how the rich natural variety of weather phenomena can be systematically influenced by climate. Appreciating how the atmosphere, where the weather occurs, interacts with the oceans, the land surface and its vegetation, and land and sea ice within the climate system is a key to understanding how influences external to this system can cause change. One of those influences is the effect of human activities, especially those that change the atmospheric composition with long-lived greenhouse gases.
Climate fluctuates naturally on very long time scales (thousands of years), and it is the rapidity of the projected changes that are a major source of concern. The possible impacts of the projected changes and how society has responded in the past and can in the future are also described. Everyone will be affected one way or another. So this is an important topic, yet it is one about which a certain amount of disinformation exists. Therefore it is as well to understand the issues in climate change and how these may affect each and every one of us. What we should do about the threats, given the uncertainties, is very much a choice that depends upon values, such as how much we should be stewards for the planet and its finite resources for the future generations. Many people favor a precautionary principle, "better safe than sorry," and err on the side of taking actions to prevent a problem that might not be as bad as feared. This book helps provide the knowledge and enlightenment desirable to ensure that the debate about this can be a public one and carried out by people who are well informed.
Kevin E Trenberth
October 1999