A variable is a function that maps one type of information to another.
The blueprint of a variable is its dimensionality: the dimensions of its domain (to what it maps things) and its range (what it maps). The entire Earth system can represented with a set of variables or system descriptors.
Examples
Seawater temperature (atmosphere)
Seawater Temperature is a variable that maps a single value (range: °K), to four dimensions (domain: longitude, latitude, elevation and absolute time).
- HADIsst1
- IPCC AR6 WG1 Atlas - CMIP6
- BRIDGE climate data
Global richness of genera (biosphere)
This variable (range: # of genera), domain (absolute time, set of organisms).
- Sepkoski’s genus level diversity curves
Relationship to data items
The basic idea of the chronosphere is that every data product can be described as a manifestation of a variable, i.e. it becomes a value that it takes.
We can trace how our understanding of the Earth System evolves in a secondary (knowledge) time dimension.