This paper first describes the nature of short term variability of the coupled atmosphere‐ocean‐biosphere system as shown by analysis and diagnosis of observations during the past 100 years. By ‘‘short term’’ we mean those fluctuations of the coupled climate system whose time scales range from 10 days to 1000 days. We have deliberately excluded any discussion of short range weather forecasting (less than 10 days) and decadal changes (more than 1000 days).