Global Analysis - May 2015
Global Surface Temperature Data Transition
Global Surface Temperature Data Transition
Effective with this (May 2015) monthly climate report, NCEI transitions to updated versions of its land and ocean surface temperature datasets. When combined, these merged datasets are now known as NOAAGlobalTemp (formerly MLOST). This page provides answers to some questions regarding the updated data.
Q. What are the new versions of land data and ocean data in NOAAGlobalTemp?
A. The new version of NOAAGlobalTemp uses GHCN-Monthly version 3.3.0 (updated from version 3.2.2.) for land surface air temperature data and ERSST version 4.0.0 (updated from version 3b) for ocean surface temperature data.
Q. What are the corrections to the ERSST dataset?
A. Version 4 of the ERSST dataset improves or corrects for several factors related to sea-surface temperature (SST) measurements. These include: updated and substantially more complete input data from ships and buoys, improved metadata associated with these observations, updated SST quality control procedures, revised SST anomaly evaluation methods, updated corrections to ship SSTs using nighttime marine air temperature, accounting for differences inherent in buoy (relative to ship-borne) observations, and improved methods of identifying and using persistent statistical relationships between neighboring regions to help validate observations and address missing data. Complete information on these changes is available in Huang et al. (2015).
Q. What are the corrections to the GHCN-Monthly dataset?
A. The changes to the land dataset were technical in nature. Some accommodated the consolidation of certain upstream sources. Most changes did not add or subtract data from GHCN-M, but resulted in changed flags and metadata associated with some stations. Some corrections did add or affect data from a small number of stations. These included: incorporating recently-available Australian data from late 2011, minor improvements to quality control for duplicate stations and outliers, and how pairwise homogeneity adjustment algorithms handle: (a) stations in very remote locations, (b) some composited ("threaded") US stations, and (c) stations with long gaps in their records. These changes, and their impacts, are fully detailed in the NCEI Technical Report related to GHCN-M version 3.3.0.
Q. How did these changes impact the global temperature record?
A. The overall character of the global temperature time-series remains largely unchanged, but some years and periods were affected by the change to version 4.0.0 of ERSST. The changes are visible here. Periods with relatively more noticable differences are: the years during and prior to World War Two (related to improved metadata associated with ship-borne observation type), and the 21st century (related to corrections that account for the growing use of buoy observations during these years). There are also minor differences after World War Two due to corrections that account for evolving changes in observing technologies from buckets to ship intake and hull measurements. The GHCN-M transition had virtually no impact on the global temperature timeseries, as the corrections affected a small number of stations.
Q. How will this change the ranks for annual temperatures?
A. 2014 remains the warmest year on record in the new version, by roughly the same margin as in the previous version. 2010 remains the 2nd warmest year, but is no longer tied with 2005 in that rank. Nine of the previous version's ten warmest years remain among the ten warmest of the new version, although the relative ranks of three through ten are reordered in places. A list of before and after ranks is available here.
Q. In general, why do datasets transition?
A. The curation and stewardship of historical weather and climate data, like any vital records, must account for changes over time. These may include: the introduction or discovery of new source data (such as the digitizing of records previously held on paper), changes in the situation or usage policies of data providers, progress in the scientific understanding of data and related analysis (such as the relationship between buoy and ship-borne data), improved quality control techniques, and evolving computational and storage technologies.
Q. How is this new dataset related to the Karl et al. (2015) paper published in Science?
A. The SST dataset used in the new NOAAGlobalTemp is the same as that used in Karl et al. (2015). The Karl et al. (2015) article used a different dataset for its land-based data. This dataset, with additional updates, is expected to be transitioned into NOAAGlobalTemp operations by early 2016, subject to any revisions arising from internal or external review.
Gleason, B., C. Williams, M. Menne, J. Lawrimore, 2015: Modifications to GHCN-Monthly (version 3.3.0) and USHCN (version 2.2.5) processing systems. GHCN-M Technical Report No. GHCNM-15-01. National Centers for Environmental Information, Asheville, NC. 20 pp. http://www1.ncdc.noaa.gov/pub/data/ghcn/v3/techreports/Technical%20Report%20GHCNM%20No15-01.pdf
Huang, B., V.F. Banzon, E. Freeman, J. Lawrimore, W. Liu, T.C. Peterson, T.M. Smith, P.W. Thorne, S.D. Woodruff, and H-M Zhang, 2015: Extended Reconstructed Sea Surface Temperature Version 4 (ERSST.v4). Part I: Upgrades and Intercomparisons. J. Climate, 28, 911-930. http://dx.doi.org/10.1175/JCLI-D-14-00006.1
Karl, T.R., A. Arguez, B. Huang, J.H. Lawrimore, J.R. McMahon, M.J. Menne, T.C. Peterson, R.S. Vose, and H-M Zhang, 2015: Possible artifacts of data biases in the recent global surface warming hiatus. Science aaa5632. Published online 4 June 2015. dx.doi.org/10.1126/science.aaa5632.
Liu, W., B. Huang, P.W. Thorne, V.F. Banzon, H-M Zhang, E. Freeman, J. Lawrimore, T.C. Peterson, T.M. Smith, and S.D. Woodruff, 2015: Extended Reconstructed Sea Surface Temperature Version 4 (ERSST.v4): Part II. Parametric and Structural Uncertainty Estimations. J. Climate, 28, 931-951. http://dx.doi.org/10.1175/JCLI-D-14-00007.1