Instrumental temperature record

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.^[1] 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.^[2] 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.

The longest-running temperature record is the Central England temperature data series, which starts in 1659. The longest-running quasi-global records start in 1850.^[3] For temperature measurements in the upper atmosphere a variety of methods can be used. This includes radiosondes launched using weather balloons, a variety of satellites, and aircraft.^[4] Satellites can monitor temperatures in the upper atmosphere but are not commonly used to measure temperature change at the surface. Ocean temperatures at different depths are measured to add to global surface temperature datasets. This data is also used to calculate the ocean heat content.

The data clearly shows a rising trend in global average surface temperatures (i.e. global warming) and this is due to emissions of greenhouse gases from human activities. The global average and combined land and ocean surface temperature show a warming of 1.09 °C (range: 0.95 to 1.20 °C) from 1850–1900 to 2011–2020, based on multiple independently produced datasets.^[5]: 5 The trend is faster since 1970s than in any other 50-year period over at least the last 2000 years.^[5]: 8 Within that upward trend, some variability in temperatures happens because of natural internal variability (for example due to El Niño–Southern Oscillation).