Tiempo Climate Portal

Global surface air temperature

The global surface air temperature record is the main indicator of the state of the global climate system. It is commonly used in efforts to detect the effects of greenhouse gas emissions on climate.

The global, Northern Hemisphere and Southern Hemisphere temperature records can be downloaded from the Climatic Research Unit web site. The data are presented as monthly and annual departures in degrees Celsius from the relevant monthly mean for the period 1961-90.

Discussion

The global surface air temperature record shows that an overall warming of about 0.5°Celsius has occurred since the middle of the 19th century, in keeping with model predictions of the effect of the changing atmospheric composition over that time.

The warming has, however, been variable in strength with two periods of marked warming — during the 1920s and 1930s and in recent decades — punctuating periods when global temperature remained relatively stable.

The records for the Northern and Southern Hemisphere show similar trends.

Accounting for the variations in large-scale surface air temperature is a major focus of climate research.

The global temperature record is based on many millions of observations taken at standard meteorological stations on land and by so-called ships of opportunity in marine areas.

The reliability of the record has been subject to considerable attention. The spatial representativeness of the record is obviously more limited in the earlier years but even during the 19th century it is sufficient to define long-term trends (though perhaps not year-to-year variations).

Data availability

The gridded surface air temperature data set on which the large-scale averages are based can be downloaded. Other data sets are also available.

On the Web

Information sheets on the global temperature record and causes of temperature change are available.

Acknowledgements

The gridded global temperature data set used to produce large-scale temperature averages is maintained by the , University of East Anglia, and the Hadley Centre in the United Kingdom.

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