Limitations on Absolute Temperature Data

Absolute Temperature Data

• Climate scientists make their calculations based on daily readings taken at many locations around the world, from stations in the Arctic to ships at sea. These readings are the absolute temperature data. For instance, if a weather station in Maine in January records a temperature of 25 degrees Farenheit, then 25 degrees is the absolute temperature for that location on that date. However, this figure is of limited use on its own in climate science.

Anomalies

• Instead of using the absolute temperature data collected every day, scientists study the anomalies between the absolute temperature data and the average baseline temperature over a period of years. This is because the absolute temperature data cannot easily be compared between one data set and another, and the anomalies provide a way to standardize all of the information into a form that can be compared directly. This allows climate scientists to observe not only the actual temperatures, but temperature trends.

Problems with Absolute Temperature Data

• One of the problems with trying to use absolute temperature data directly is that not all of it is available every day. For instance, if scientists collect data from 10,000 locations on one day, and one of those locations is a weather station in Alaska, then this weather station from a cold climate will usually bring the average temperature down. If, on a particular day, that station is not functioning or is unable to communicate, its data would not be included in the average and the daily average temperature would appear to be warmer even if it actually was not.

Calculating Anomalies

• To convert absolute temperature data into a more useful form, scientists take an average of temperatures for a particular location over a period of at least 30 years. This is the baseline temperature for that location on that date. When the absolute temperature data is collected for that date and location, it may be higher or lower than the baseline temperature. If the temperature is higher than baseline, it is called a positive anomaly. If it is lower than baseline it is a negative anomaly. When anomalies from all the stations of the world are combined and averaged, scientists are able to determine if the planet as a whole was cooler or warmer than average on that day, and missing stations or differences in location will not skew the result.