The Climatic Research Unit (CRU) at the University of East Anglia (UEA) has, since 1982, made available gridded datasets of surface temperature data over land areas and averages for the Northern and Southern Hemispheres and the Globe. Until the development of the internet these were made available via various media. These datasets (the latest being CRUTEM4, http://www.cru.uea.ac.uk/cru/data/temperature/) have been developed from data acquired from weather stations around the world. Almost all these weather stations are run by National Meteorological Services (NMSs) who exchange these data over the CLIMAT network, which is part of the World Meteorological Organization's (WMO) Global Telecommunications System (GTS). Much of the original data in the early 1980s came from publications entitled 'World Weather Records, WWR'. We also make use of data available from the National Climatic Data Center in Asheville, North Carolina (their Global Historical Climatology Network, GHCN). We are also constantly striving to find additional, and homogenized, data from a wide range of sources (see details of earlier work in the publications below and the references in Jones et al. 2012). Both the gridded datasets and the station data archive have evolved over the years and we introduced dataset version numbers in the early 1990s. The methodology we have used in developing the gridded datasets has been described in numerous publications in the climate literature (see list at the end of this document and also http://www.cru.uea.ac.uk/cru/data/temperature/ and the linked FAQs).

Our latest station dataset CRUTEM4 was published in March 2012, and all the station data used are available (on the CRU site and also at http://www.metoffice.gov.uk/hadobs/crutem4/data/download.html). Reading the scientific paper about the dataset (Jones et al. 2012) clearly indicates that most of the homogeneity adjustments that have been applied to the station data have been made by NMSs. The sources (web pages, reports and scientific papers) have been documented in the above paper. The only remaining CRU adjustments are those we applied during the mid-1980s (documented here http://www.cru.uea.ac.uk/st/). There were 312 of these at that time (~10% of the total), and there are now just over 219 (now ~5%) - all for periods before 1980. The number has been reduced due to the replacement of data for some countries by newer, improved data from some NMSs. In the mid-1980s, CRU realized that homogeneity was best accomplished by each NMS, and this was stated in Jones and Moberg (2003). None of the station air temperature series from the mid-1980s up to the present include any CRU adjustments to station temperature data. Instead we incorporated homogeneity-adjusted station series produced by NMSs. The availability and number of these have become more numerous in recent years.

There is often much discussion about exactly what ‘raw' means in this context. Is it the data at every observation time or is it just the monthly average computed by the NMS for each station? With the data for each observation time, does this include changes made to values by NMSs in the course of basic quality control?  The station data CRU have made available are monthly averages from the NMSs and include as much homogeneity assessed and adjusted data as possible and details of what has been done and where. Apart from our adjustments made in the mid-1980s (see above), the rest of the data are directly from the NMSs – also released through CLIMAT messages or through the various World Weather Record (WWR) volumes (by the Smithsonian Institution up to 1950 and by NCDC since then in decade books). GHCN maintains a dataset of unadjusted station temperatures, but this uses the same sources we access. The WWR volumes for the period before 1950 clearly reveal that the compilers looked at the quality of the station data and made some adjustments. Also many of the series submitted by NMSs to later WWR volumes were assessed by each NMS before submission. So, although the GHCN dataset is stated to be unadjusted, the correct title should probably be ‘unadjusted by NCDC'. It is for this reason that in Jones et al. (2012) we stated that the only true source of the original raw temperature data are the NMSs.

Since the early 1980s, some NMSs, other organizations and individual scientists have given or sold us (see Hulme, 1994, for a summary of European data collection efforts) additional data for inclusion in the gridded datasets, often on the understanding that the data are only used for academic purposes with the full permission of the NMSs, organizations and scientists and that the original station data are not passed onto third parties. This is not just temperature data, but station data for some other variables, particularly precipitation. Below, we list the agreements that we still hold. Additional agreements are unwritten and relate to partnerships we've made with scientists around the world and visitors to the CRU over this period. In some of the examples given, it can be clearly seen that our requests for data from NMSs have always stated that we would not make the data available to third parties. We included such statements as standard from the 1980s, as that is what many NMSs requested.

The inability of some agencies to release climate data held is not uncommon in climate science today. The Dutch Met Service (KNMI) run the European Climate Assessment and Dataset (ECA&D, http://eca.knmi.nl/) project. They are able to use much data in their numerous analyses, but they cannot make all the original daily station temperature and precipitation series available because of restrictions imposed by some of the data providers. Currently they can make available about 70% of the station data series they use. A series of ongoing workshops (see Peterson and Manton, 2008 for details and also http://www.clivar.org/organization/etccdi/resources/workshops-extremes-indices ) has been held in diverse regions of the world to produce analyses of trends in extremes. NMSs are generally happy to release derived products from their data, even if they restrict access to their digital climate archives. A third example is the Global Precipitation Climatology Centre (http://gpcc.dwd.de), run by the German Weather Service (DWD) who make various versions of gridded precipitation datasets freely available, but due to restrictions imposed by data providers are not able to give access to any of the station monthly precipitation totals. The problem is a generic issue and arises from the need of many NMSs to be or aim to be cost neutral (i.e. to sell the data to recoup the costs of making observations and preparing the data).

What ECA&D and GPCC are doing is producing gridded products, which can be made freely available for anyone to use. The developers cannot make all the station data available, however.  ECA&D make what they can available, but GPCC has a policy of not making any available. Station data availability is often most acute when it comes to daily precipitation data.  Frei and Schar (1998) and Yatgai et al. (2009) are further examples of where gridded datasets are developed but the original station data cannot be made available.

We receive numerous requests for station data (not just monthly temperature averages, but precipitation totals and pressure averages as well). Requests come from a variety of sources, often for an individual station or all the stations in a region or a country. Sometimes these come because the data cannot be obtained locally or the requester does not have the resources to pay for what some NMSs charge for the data. We point enquirers to the GHCN web site. We are, however, now able to supply the station temperature data used in CRUTEM4 and the previous version CRUTEM3. We also recommend that users make use of the gridded products as the series are always more complete than the original station series.

We rely on the CLIMAT network for updating CRU data series in near-real time. After quality control at the Hadley Centre these data are made available (since 2000) at http://hadobs.metoffice.com/crutem3/data/station_updates/. We thus make extensive use of the CLIMAT network as well as the publication Monthly Climatic Data for the World (MCDW) produced by NCDC, Asheville. Within the next one to two years we will replace some of the CLIMAT data with quality-controlled station data from a small number of countries (see Jones et al. 2012 for details). We will also use additional homogenized station data when work is completed from an NMS or in a scientific publication.

Some years ago, WMO enacted Resolution 40 (http://www.map.meteoswiss.ch/map-doc/WMO/WMOresol40.htm) which covers the exchange of meteorological data and many data products and services produced by NMSs. This resolution applies only to NMSs and whilst Annex 1 of this resolution implies that much data should be freely available for research and operational uses (commercial is discussed separately), many NMSs still impose conditions and charge for access (see the earlier discussion related to KNMI and GPCC).

 

Files

 

References

  • Frei, C. and Schär, C., 1998: A precipitation climatology of the Alps from high-resolution rain-gauge observations. Int. J. Climatol. 18, 873-900.
  • Hulme, M., 1994: The cost of climate data: A European experience. Weather 49, 168-176.
  • Jones, P.D. and Moberg, A., 2003: Hemispheric and large-scale surface air temperature variations: An extensive revision and an update to 2001. J. Climate 16, 206-223.
  • Jones, P.D., Lister, D.H., Osborn, T.J., Harpham, C., Salmon, M., Morice, C.P. 2012: Hemispheric and large-scale land surface air temperature variations: An extensive revision and an update to 2010. J. Geophys. Res. 117, D05127, doi:10.1029/2011JD017139.
  • Peterson, T.C. and Manton, M.J., 2008: Monitoring changes in climate extremes: a tale of international collaboration. Bull. Amer. Meteorol. Soc. 89, 1266-1271.
  • Yatgai, A., Arakawa, O., Kamiguchi, K., Kawamoto, H., Nodzu, M.I. and Hamada, A., 2009: A 44-year daily gridded precipitation dataset for Asia based on a dense network of rain gauges. SOLA 5, 137-140, doi:10.2151/sola.2009-035.

 

Literature describing the development of CRU land temperature datasets

  • Jones, P.D., Lister, D.H., Osborn, T.J., Harpham, C., Salmon, M., Morice, C.P. 2012: Hemispheric and large-scale land surface air temperature variations: An extensive revision and an update to 2010. J. Geophys. Res. 117, D05127, doi:10.1029/2011JD017139.
  • Morice, C.P., Kennedy, J.J., Rayner, N.A. and Jones, P.D., 2012: Quantifying uncertainties in global and regional temperature change using an ensemble of observational estimates: the HadCRUT4 dataset. Journal of Geophysical Research, 117, D08101, doi:10.1029/2011JD017187.
  • Brohan, P., Kennedy, J., Harris, I., Tett, S.F.B. and Jones, P.D., 2006: Uncertainty estimates in regional and global observed temperature changes: a new dataset from 1850. J. Geophys. Res. 111, D12106, doi:10.1029/2005JD006548.
  • Jones, P.D. and Moberg, A., 2003: Hemispheric and large-scale surface air temperature variations: An extensive revision and an update to 2001. J. Climate 16, 206-223.
  • Jones, P.D., New, M., Parker, D.E., Martin, S. and Rigor, I.G., 1999: Surface air temperature and its variations over the last 150 years. Reviews of Geophysics 37, 173 199.
  • Jones, P.D., Wigley, T.M.L. and Kelly, P.M., 1982. Variations in surface air temperatures, Part 1: Northern Hemisphere, 1881-1980. Monthly Weather Review 110, 59-70.
  • Jones, P.D., Raper, S.C.B., Bradley, R.S., Diaz, H.F., Kelly, P.M. and Wigley, T.M.L., 1986: Northern Hemisphere surface air temperature variations: 1851-1984. Journal of Climate and Applied Meteorology 25, 161-179.
  • Jones, P.D., Raper, S.C.B. and Wigley, T.M.L., 1986: Southern Hemisphere surface air temperature variations: 1851-1984. Journal of Climate and Applied Meteorology 25, 1213 1230.
  • Jones, P.D., Wigley, T.M.L. and Wright, P.B., 1986: Global temperature variations, 1861-1984. Nature 322, 430-434.
  • Jones, P.D., 1988: Hemispheric surface air temperature variations: Recent trends and an update to 1987. Journal of Climate 1, 654-660.
  • Jones, P.D., Groisman, P.Ya., Coughlan, M., Plummer, N., Wang, W-C. and Karl, T.R., 1990: Assessment of urbanization effects in time series of surface air temperature over land. Nature 347, 169-172.
  • Jones, P.D. and Briffa, K.R., 1992: Global surface air temperature variations over the twentieth century: Part 1 Spatial, temporal and seasonal details. The Holocene 2, 165-179.
  • Jones, P.D., 1994: Hemispheric surface air temperature variations: a reanalysis and an update to 1993. Journal of Climate 7, 1794 1802.
  • Bradley, R.S., Kelly, P.M., Jones, P.D., Goodess, C.M. and Diaz, H.F., 1985: A Climatic Data Bank for Northern Hemisphere Land Areas, 1851-1980, U.S. Dept. of Energy, Carbon Dioxide Research Division, Technical Report TRO17, 335 pp.
  • Jones, P.D., Raper, S.C.B., Santer, B.D., Cherry, B.S.G., Goodess, C.M., Kelly, P.M., Wigley, T.M.L., Bradley, R.S. and Diaz, H.F., 1985: A Grid Point Surface Air Temperature Data Set for the Northern Hemisphere, U.S. Dept. of Energy, Carbon Dioxide Research Division, Technical Report TRO22, 251 pp.
  • Jones, P.D., Raper, S.C.B., Cherry, B.S.G., Goodess, C.M. and Wigley, T.M.L., 1986: A Grid Point Surface Air Temperature Data Set for the Southern Hemisphere, 1851-1984, U.S. Dept. of Energy, Carbon Dioxide Research Division, Technical Report TR027, 73 pp.