Can historical temperature data records be trusted? Haven't they been skewed by non-climate factors like instrument changes and "urban heat islands"?

January 23, 2014

Our global historical temperature records can be trusted to represent changes in Earth's temperature over long time periods. Different scientific and technical teams in the United States and other countries have assessed weather stations' historical temperature data and concluded that the data are of high quality and are well suited for studies of global temperature changes from 1880 to 2012.

If ignored, non-climate factors can skew individual stations' data records by sometimes introducing an "artificial" cooling trend and sometimes introducing an "artificial" warming trend. Important examples are changes in the type of measuring instrument used in the record and the effect of buildings and pavement in the vicinity of temperature measuring stations (i.e., the "urban heat island effect"). But these and other known problems have not been ignored; rather, steps have been taken to remove or minimize non-climate impacts on the long-term records. These steps are well documented and have been undertaken in a transparent way. The non-climate artifacts have been identified and removed from station data records in cases where there is high confidence that it can be accomplished without harming the data quality. In cases where there is reason to believe that station data contain significant errors that cannot be corrected, those data are removed from national and global averages.

Although the possibility of unknown or uncorrected errors in the land surface temperature data cannot be completely excluded, many other lines of evidence confirm that our world has warmed over multiple decades:

Okpilak Glacier

The marked retreat of Okpilak Glacier in Brooks Range, Alaska, is one example of glacier retreat worldwide. Images from the National Snow and Ice Data Center (NSIDC) Glacier Photograph Collection.


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