| Summary: | The idea that the climate of Earth has changed is not new. Much evidence has been collected from the sedimentary record indicating periodic as well as secular changes in climate parameters such as surface temperature, precipitation amount, and ice extent and abundance, on many time scales. But in the last quarter of the twentieth century, there are several new elements in the way climate change is perceived. One is the view that human activity is having an impact on climatic conditions, on a global scale. The conclusion of recent studies indicating that anthropogenic chlorofluorocarbons are the root cause of a measured secular decrease in atmospheric ozone column abundance over the Antarctic in spring, illustrates this point (e.g., Solomon 1990).
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