Global Temperature Data Sets: Overview & Comparison Table

Global surface temperature data sets are an essential resource for monitoring and understanding climate variability and climate change. The most commonly used data sets combine historical observations of near surface air temperatures at land stations with global data sets of sea surface temperatures (SST) obtained from a changing mix of ship-based and buoy measurements. While the concept of these data sets is fairly simple, their construction is challenging due to difficulties in obtaining data, documenting and accounting for changes in instrumentation and observing practices, addressing changes in station location and local land use, understanding random measurement errors, and deciding where and how to infill missing data in space and time.

The three most highly cited combined land temperature and SST data sets are NOAA's MLOST, NASA's GISTEMP, and  the UK's HadCRUT. A new merged land-ocean temperature data set is available from the Berkeley Earth group. The University of Delaware and berkeleyearth.org produce global land-only surface temperature data sets. HadCRUT also has a land-only version, CRUTEM. Each group has approached the above challenges somewhat differently. The final data sets differ in their spatial coverage, spatial resolution, starting year, and degree of interpolation (only HadCRUT is uninterpolated). Most of these data sets are presented as anomalies (departures from baseline, long-term mean temperatures); only the Delaware data provide absolute temperatures for each timestep, while the other projects provide a baseline climatology to which the anomalies may be compared. Numerous comparisons of global and hemispheric mean temperature anomaly timeseries calculated from these data sets have been made, showing highly consistent variations and trends. Nonetheless, users doing more analysis than the global mean temperature will find important distinctions among the data sets.

Besides the in-situ based data sets summarized here, other estimates of global temperatures (since the 1970s) are based on satellite measurements such as from the MSU and AIRS instruments, or on atmospheric reanalyses.