Global surface temperature


Global surface temperature is the average temperature of Earth's surface at a given time. It is a combination of sea surface temperature and the near-surface air temperature over land, weighted by their respective areas. Temperature data comes mainly from weather stations and satellites. To estimate data in the distant past, proxy data can be used for example from tree rings, corals, and ice cores. Observing the rising GST over time is one of the many lines of evidence supporting the scientific consensus on climate change, which is that human activities are causing climate change. Alternative terms for the same concept are global mean surface temperature or global average surface temperature.
Series of reliable temperature measurements in some regions began in the 1850—1880 time frame. 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. 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. 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.
GMST is often further aggregated by year or month. Through 1940, the average annual GMST increased, but was relatively stable between 1940 and 1975. Since 1975, it has increased by roughly 0.15 °C to 0.20 °C per decade, to at least 1.1 °C above 1880 levels. The current annual GMST is about, though monthly temperatures can vary almost above or below this figure.
The global average and combined land and ocean surface temperature show a warming of 1.09 °C from 1850–1900 to 2011–2020, based on multiple independently produced datasets. The trend is faster since the 1970s than in any other 50-year period over at least the last 2000 years. Within that upward trend, some variability in temperatures happens because of natural internal variability.
The global temperature record shows the changes of the temperature of the atmosphere and the oceans through various spans of time. There are numerous estimates of temperatures since the end of the Pleistocene glaciation, particularly during the current Holocene epoch. Some temperature information is available through geologic evidence, going back millions of years. More recently, information from ice cores covers the period from 800,000 years ago until now. Tree rings and measurements from ice cores can give evidence about the global temperature from 1,000-2,000 years before the present until now.

Definition

The IPCC Sixth Assessment Report defines global mean surface temperature as the "estimated global average of near-surface air temperatures over land and sea ice, and sea surface temperature over ice-free ocean regions, with changes normally expressed as departures from a value over a specified reference period".
Put simply, the global surface temperature is calculated by averaging the temperature at the surface layer of the ocean and over land.
In comparison, the global mean surface air temperature is the "global average of near-surface air temperatures over land, oceans and sea ice. Changes in GSAT are often used as a measure of global temperature change in climate models."
Global temperature can have different definitions. There is a small difference between air and surface temperatures.

Temperature data from 1850 to the present time

Total warming and trends

Changes in global temperatures over the past century provide evidence for the effects of increasing greenhouse gases. When the climate system reacts to such changes, climate change follows. Measurement of the GST is one of the many lines of evidence supporting the scientific consensus on climate change, which is that humans are causing warming of Earth's climate system.
The global average and combined land and ocean surface temperature, show a warming of 1.09 °C from 1850–1900 to 2011–2020, based on multiple independently produced datasets. The trend is faster since the 1970s than in any other 50-year period over at least the last 2000 years.
Most of the observed warming occurred in two periods: around 1900 to around 1940 and around 1970 onwards; the cooling/plateau from 1940 to 1970 has been mostly attributed to sulfate aerosol. Some of the temperature variations over this time period may also be due to ocean circulation patterns.
Land air temperatures are rising faster than sea surface temperatures. Land temperatures have warmed by 1.59 °C from 1850–1900 to 2011–2020, while sea surface temperatures have warmed by 0.88 °C over the same period.
For 1980 to 2020, the linear warming trend for combined land and sea temperatures has been 0.18 °C to 0.20 °C per decade, depending on the data set used.
It is unlikely that any uncorrected effects from urbanisation, or changes in land use or land cover, have raised global land temperature changes by more than 10%. However, larger urbanisation signals have been found locally in some rapidly urbanising regions, such as eastern China.

Methods

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.

Early temperature records

The longest-running temperature record is the Central England temperature data series, a single-location data set that starts in 1659.
On 15 December 2025, the Copernicus Programme's Earth System Science Data released the GloSAT reference analysis, a gridded data set of air temperature change across global land and ocean extending back to the 1780s, using marine air temperature observations rather than the sea surface temperature measurements.
Before GloSAT's release, the period for which reasonably reliable instrumental records of near-surface land temperature exist with quasi-global coverage was generally considered to begin around 1850. Earlier records exist, but with sparser coverage, largely confined to the Northern Hemisphere, and less standardized instrumentation.
The temperature data for the record come from measurements from land stations, ships, and buoys. On land, temperatures are measured either using electronics sensors, or mercury or alcohol thermometers which are read manually, with the instruments being sheltered from direct sunlight using a shelter such as a Stevenson screen. The sea record consists of ships taking sea temperature measurements, mostly from hull-mounted sensors, engine inlets or buckets, and more recently includes measurements from moored and drifting buoys. The land and marine records can be compared.
Areas that are densely populated tend to have a high density of measurement 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.
Land and sea measurement and instrument calibration is the responsibility of national meteorological services. Standardization of methods is organized through the World Meteorological Organization.
Most meteorological observations are taken for use in weather forecasts. Centers such as European Centre for Medium-Range Weather Forecasts show instantaneous map of their coverage; or the Hadley Centre show the coverage for the average of the year 2000. Coverage for earlier in the 20th and 19th centuries would be significantly less. While temperature changes vary both in size and direction from one location to another, the numbers from different locations are combined to produce an estimate of a global average change.

Satellite and balloon temperature records (1950s–present)

measurements of atmospheric temperature at various altitudes begin to show an approximation of global coverage in the 1950s. Since December 1978, microwave sounding units on satellites have produced data which can be used to infer temperatures in the troposphere.
Several groups have analyzed the satellite data to calculate temperature trends in the troposphere. Both the University of Alabama in Huntsville and the private, NASA funded, corporation Remote Sensing Systems find an upward trend. For the lower troposphere, UAH found a global average trend between 1978 and 2019 of 0.130 degrees Celsius per decade. RSS found a trend of 0.148 degrees Celsius per decade, to January 2011.
In 2004 scientists found trends of +0.19 degrees Celsius per decade when applied to the RSS dataset. Others found 0.20 degrees Celsius per decade up between 1978 and 2005, since which the dataset has not been updated.
The most recent climate model simulations give a range of results for changes in global-average temperature. Some models show more warming in the troposphere than at the surface, while a slightly smaller number of simulations show the opposite behaviour. There is no fundamental inconsistency among these model results and observations at the global scale.
The satellite records used to show much smaller warming trends for the troposphere which were considered to disagree with model prediction; however, following revisions to the satellite records, the trends are now similar.

Global surface and ocean datasets

The methods used to derive the principal estimates of global surface temperature trends are largely independent from each other and include:
These datasets are updated frequently, and are generally in close agreement with each other.