How to Read the Figure:
Variability or variance refers to the range of values between a particular maximum and minimum over time. The horizontal X axis begins on the left with the formation of the Earth 4.5 billion years ago, with orbital cycles occurring within the 100,000 year time scale, NAO and PDO within the 100 year decadal time scale, and the diurnal cycle (daily rotation of Earth on its axis) occurring at 0.0027 of a year. The vertical Y axis show relative variability but is not based on formal measurements. See Overview of Climate Processes for more.

Generally, the shorter the time scale, the more impact on a local spatial scale, and the longer the time scale, the bigger the impact on the global scale. Weather, occurring in a matter of hours to weeks, can vary even at local levels, while climate processes such as orbital forcing can change the climate of the entire planet.

Not all climate experts will necessarily agree on how the figure presents relative climate change. This figure in some respects overgeneralizes and over-simplifies climate processes, and in particular it does not show the interactions of variability over varying time scales. This figure is intended as a mental model to provide a general "powers of ten" overview of climate variability, and to convey the basic complexities of climate dynamics for a general science savvy audience. Throughout the website, references and links to additional information are made available for additional information.

Climate scientists often stress that because a particular phenomenon is called an oscillation, it does not necessarily mean there is a particular oscillator causing the pattern. Some prefer to refer to such processes as variability.

What is variability?

A short definition of variability is "the range of change," and in this case variability refers to the range of climate change caused by various forces through time. The Climate TimeLine has been inspired in part by the original work of NOAA's J. Murray Mitchell who in 1976 wrote a paper on climate change entitled "An Overview of Climatic Variability and Its Causal Mechanisms" (Mitchell, 1976.)

The following interactive graphic is designed to build on Mitchell's original conceptual framework for examining the basic climatic processes and forces.

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