The greenhouse gases

"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 inad