Last Updated: May 16, 2011

Effective May 2, 2011, the Global Historical Climatology Network-Monthly (GHCN-M) version 3 dataset of monthly mean temperature replaced GHCN-M version 2 monthly mean temperature dataset. Beginning with the April 2011 State of the Climate Report, GHCN-M version 3 will be used for NCDC climate monitoring activities, including calculation of global land surface temperature anomalies and trends. It will also be merged with the Extended Reconstruction Sea Surface Temperature (ERSST) version 3b dataset to form the merged land and ocean surface temperature dataset, which is used to calculate the global average temperature from 1880 to present.

For information on the differences between GHCN-M v2 versus v3, please see the Summary of Recent Changes in the GHCN-M Temperature Dataset and Merged Land-Ocean Surface Temperature Analyses document found at the following ftp site:

ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/blended/ghcnm-v3.pdf

RECENT CHANGES TO THE GLOBAL MERGED LAND AND OCEAN TEMPERATURE GRID FILE:

As of May 16, 2011, the merged land and ocean surface temperature grid that uses the GHCN-M v3 and ERSST v3b will be named as follows:

ncdc-merged-sfc-mntp.dat.gz

This file will be publicly available at the following ftp site:

ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/blended/

Please note that GHCN-M v2 mean temperature dataset will continue to be updated through May 30, 2011, but no support for this version of the dataset will be provided. The merged land and ocean surface temperature grid using the GHCN-M v2 and ERRST v3b will be updated until May 30th and will be made publicly available at the following ftp site:

ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/blended/usingGHCNMv2/

The filename will remain the same: ncdc_blended_merg53v3b.dat.gz

RECENT CHANGES TO THE GLOBAL MERGED LAND AND OCEAN TEMPERATURE ANOMALIES FILE:

As of May 16, 2011, all anomalies data files located in (ftp://ftp.ncdc.noaa.gov/pub/data/anomalies/) will be updated to reflect the recent changes in the GHCN-M v3 dataset transition. The filenames will remain the same despite the new version transition. However, anomalies files using GHCN-M v2 and ERSST v3b will be updated until May 30th and will be made publicly available at the following ftp site:

ftp://ftp.ncdc.noaa.gov/pub/data/anomalies/usingGHCNMv2/


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Last Updated: August 14, 2009

In July 2009, NCDC transitioned to the use of an improved Global Land and Ocean data set (Smith et al., 2008) which allows better analysis of temperatures throughout the record, with the greatest improvements in the late nineteenth century and since 1985. Improvements in the late nineteenth century are due to improved tuning of the analysis methods.