A temperature anomaly is the difference from an average or baseline temperature. The baseline temperature is typically computed by averaging 30 or more temperatures over a certain reference period, often called a base period. Temperature anomalies are a measure of temperature compared to a reference temperature, which is often calculated as an average of temperatures over a reference period. Records of global average surface temperature are usually presented as anomalies rather than as absolute temperatures. Using reference values computed for distinct areas over the same time period establishes a baseline from which anomalies are calculated, so that normalized data is used to more accurately compare temperature patterns to what is normal.

Temperature anomalies can be positive or negative, indicating whether the observed temperature was warmer or cooler than the reference temperature, respectively. Anomalies provide a frame of reference that allows more meaningful comparisons between locations and more accurate calculations of temperature trends. However, anomalies alone are not sufficient to characterize exceptionality of temperature values. The standard deviation quantifies the degree of variation of a datasets values.

Temperature anomalies can be used to study climate change and its effects on the environment. For example, NASAs Earth Observatory uses land surface temperature anomalies to monitor changes in temperature patterns over time.