How do scientists measure global surface temperatures?
Thermometers have recorded air temperature at weather stations or surface seawater temperature from ships for many decades, with almost global coverage extending back to 1861. Instruments on satellites have monitored infrared radiation for many years, which is then converted to temperature to provide global records back to 1979. In addition, proxy records—data relating to climate, such as tree rings and ice cores— extend the global surface temperature record back hundreds and even thousands of years.
