The instrumental temperature record is a record of temperatures within Earth's climate based on direct measurement of air temperature and ocean temperature. Instrumental temperature records do not use indirect reconstructions using climate proxy data such as from tree rings and marine sediments. Instead, data is collected from thousands of meteorological stations, buoys and ships around the globe. Areas that are densely populated tend have a high density of measurements points. In contrast, temperature observations are more spread out in sparsely populated areas such as polar regions and deserts, as well as in many regions of Africa and South America. In the past, thermometers were read manually to record temperatures. Nowadays, measurements are usually connected with electronic sensors which transmit data automatically. Surface temperature data is usually presented as anomalies rather than as absolute values. A temperature anomaly is presented compared to a reference value, also called baseline period or long-term average). For example, a commonly used baseline period is the time period from 1951 to 1980.

Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making up a substance.