Climate variability and change

Abstract

The concepts of climate variability, due to natural processes, and of cli— mate change, related to man’s activitites, are illustrated. Different types of internal mechanisms, such as multiple equilibria and the integration of noise, are discussed. A systematic approach to discriminate between natu- ral variability and anthropogenic change indicates that the latest warming trends in the observational record can no longer be understood as “vari- ability” but is likely related to external processes, and in particular to the enhanced greenhouse effect. Finally we discuss briefly major challenges climate research will face in the coming decades.