"The Earth's climate, over the millenia of its existence, has been shaped by the cosmic forces of nature--by the cooling of the Earth's core, variations in the intensity of the Sun, changes in the tilt of our planet. These were accompanied by the remarkable alterations in the life forms our planet supported. Life itself probably emerged from the 'primeval soup' of the first oceans. The hot and humid Cretaceous period led on to the dinosaurs and pterdactyls of 100 million years ago. The last few million years have been marked by alternate Ice Ages and warm periods. Sea levels fell during the Ice Ages and rose again as ice and glaciers melted. Today's climate is being changed by events that have taken--on a cosmic timescale--but the batting of an eyelid. In the 300 years or so that have encompassed the agricultural and industrial revolutions, man has begun to replace nature as the engine of climatic change.^
Today, the activities of...human beings may be changing the climate faster than any natural event. This is a fact of life, and there is little point in pondering its morality. There is point, however, in asking where the process is leading us. Until recently, the process was inadvertent. It is no longer so. We now know that to continue increasing the concentration of certain gases in the atmosphere will inevitably lead to a warmer, and probably wetter, planet. How warm, how wet, and how soon are three of the questions that scientists are learning to answer. We await their definitive response with some trepidation. The need for a greater understanding of the problem was fully appreciated by the early 1970s, when the United Nations Environment Programme (UNEP) was created. UNEP, the World Meteorological Organization and the International Council of Scientific Unions joined forces to place the study of the greenhouse effect on a firm scientific footing.^
At that time, it was estimated that carbon dioxide levels in the atmosphere would double by the year 2030. Then came the oil price increases of the 1970s, a cut-back in the world energy consumption and a new forecast--that it would take another century to double carbon dioxide levels. Since then, we have discovered the potent potential effect of other greenhouse gases--an effect that threatens, again, to double the effective carbon dioxide level by 2030. We have come full circle, by a rather roundabout route. This publication summarizes our current [1987] knowledge of the subject in a way that is understandable to all. I hope it will stimulate widespread public interest in the subject, and spur those who can help devise policies for the protection of the Earth's climate to greater and more informed efforts." --Excerpted from the Foreword, by Mostafa K. Tolba, 1987 Executive Director of the United Nations Environment Programme, pages 2-3.
