  The spectral view of variability is a compelling and adaptable tool for
understanding variability of the climate. In Mitchell (1976) seminal paper, it
was used to express, on one graph with log scales, a very wide range of climate
variations from millions of years to days. The spectral approach is
particularly useful for suggesting causal links between forcing variability and
climate response variability. However, a substantial degree of variability is
intrinsic and the Earth system may respond to external forcing in a complex
manner. There has been an enormous amount of work on understanding climate
variability over the last decades. Hence in this paper, we address the
question: Can we (after 40 years) update the Mitchell (1976) diagram and
provide it with a better interpretation? By reviewing both the extended
observations available for such a diagram and new methodological developments
in the study of the interaction between internal and forced variability over a
wide range of timescales, we give a positive answer to this question. In
addition, we review alternative approaches to the spectral decomposition and
pose some challenges for a more detailed quantification of climate variability.
