Worldwide historical surface air temperatures


Most of the meteorological data accessed from the map in the previous page are provided by access to the public domain NASA Goddard Institute for Space Studies (GISS) web page. 

The reason for mainly using GISS data is not that this database is considered to offer the highest quality of data, compared to other fine databases located at various institutions all over the world. All these meteorological databases represent the result of careful and painstaking work during many years. Among these different databases, the GISS database has tradition for estimating the highest global surface air temperatures. But in contrast to some other databases, the GISS database follows a admirable public domain policy, including free data access not only to gridded data products, but also to the individual meteorological series.

All data are homogenized, i.e. corrected for environmental change in the surroundings of the measuring instrument and for errors arising at the point of measurement, such as due to known equipment or procedural faults, change of measuring site, change of surroundings, change of averaging method, etc. Presumably some of the data series may still be affected by a local urban heat island (UHI) effect larger than assumed by standard UHI correction techniques, or by temporal, local temperature inversions prevailing during winter periods with calm conditions in cold regions. At the moment, it difficult to correct for such potential measurement errors, as proper correction requires detailed investigations at each individual site. 

In order to reduce such effects from local heating sources, mainly stations located outside large settlements has been selected for display below. However, to ensure good geographical coverage, it has not been possible to follow this general rule strictly for all geographical regions. In addition, especially long meteorological data series have been selected where such was available.