The deviation of a measured temperature from its long-term average for a specific location and time.Temperature anomaly is the difference between a measured temperature at a given place and time and the average temperature for that same place and time over a reference period, typically 30 years. It is a way of expressing how much warmer or cooler conditions are than what is considered 'normal' for that spot. Because the anomaly removes the regular seasonal cycle and geographic variations, it lets scientists compare temperature changes across different regions and seasons on a common scale.
The concept has been used in meteorology and climatology for over a century, but it became a standard tool in the mid-20th century as global temperature datasets were assembled. No single inventor is credited; it emerged from practical needs in weather forecasting and climate monitoring.
To compute an anomaly, climatologists first establish a climatology—the long-term average temperature for each calendar day or month at a station or grid point. They then subtract that average from the actual observed temperature. The result is a positive number if conditions are warmer than average, negative if cooler. Anomalies are often averaged over large areas or the whole globe to track climate change, because they cancel out local quirks like altitude or proximity to oceans.
Temperature anomalies are the primary metric in global warming assessments, reported by agencies like NASA and NOAA to show how each year compares to the 20th-century average.
A 1°C global temperature anomaly represents a huge amount of energy—enough to heat the entire atmosphere by several degrees if it were concentrated there.







