Index

Anomalies vs. Temperature

In climate studies, temperature anomalies are often more useful than absolute temperatures. A temperature anomaly is the difference between the observed temperature and a baseline average temperature. This baseline is usually calculated by averaging 30 or more years of temperature data for a specific location.

A positive anomaly means the observed temperature was warmer than the baseline, while a negative anomaly means the observed temperature was cooler than the baseline. Unlike absolute temperatures, which can be greatly affected by factors like elevation or whether a station is in an urban or rural area, anomalies help minimize the impact of those differences. For example, a mountain top and a nearby valley might both experience a cooler-than-average summer month, but their absolute temperatures will still be quite different.

Asheville Stations

Using anomalies also helps reduce issues when stations are added, removed, or have gaps in their data. The diagram shows absolute temperatures (lines) for five nearby stations, along with the anomalies for 2008 (symbols). Notice how the anomalies all fall within a small range when compared to the wider spread of absolute temperatures. If one station—say, the coolest station at Mt. Mitchell—were removed, the average absolute temperature would shift noticeably warmer. However, because its anomaly is similar to the neighboring stations, the average anomaly would change very little.