| Function | Construct a comparison baseline |
|---|---|
| Must be stated in | Caption, methods, or metadata |
| Baseline change | Requires consistency in variable and domain |
Definition and context
A reference period makes it possible to calculate mean values against which to compare observations. In climate science, the choice should be stated in the information accompanying each product. Two anomalies with different reference periods cannot be compared as though they automatically shared the same zero.
Imagine the same temperature expressed relative to two hypothetical baselines. If one baseline is one degree warmer, the anomaly relative to it will be one degree smaller. The observation has not changed. This idea explains a shift in the scale, but actual conversions must preserve the variable, region, and aggregation period. There is no universal adjustment that can be applied to any dataset without consulting its methodology.
What we know and its limits
Introductory reference sheet. Properties and applications depend on measurement conditions; consult the sources before making comparisons.
Follow the evidence
The original sources for exploring this explanation and its limits.
- Temperature Q&As
Copernicus Climate Change Service · ECMWF
Questions about temperature, reference periods, and comparability. - Climate indicators · Temperature
Copernicus Climate Change Service · ECMWF
Difference between annual and multi-year temperature averages.
Image credits
Photo by Matheus Bertelli on Pexels · Original source · Pexels License