Physical Sciences Division

7.5 Ensuring long-term observed climate records

CDC pioneered the development of the Comprehensive Ocean-Atmosphere Data Set (COADS)-an international resource for historical weather observations over the globe. The ability to detect any future changes in regional, hemispheric, and global climate, and to make improvements in global climate models, depends crucially on the availability of high-quality retrospective data and metadata. As such, COADS forms the central oceanic ingredient for past and present National Scientific Assessments and for the Intergovernmental Panel on Climate Change, as well as for Global Atmospheric Reanalyses by US groups and by the European Centre for Medium-Range Weather Forecasts.

In 1985, the cooperating organizations issued the first version (Release 1) of this comprehensive historical record of marine meteorological data-observations from ships now extending back for over two centuries, supplemented since the late 19th century by data from oceanographic research vessels, and in recent decades from moored and drifting environmental buoys-and made them widely available and readily accessible to users. Both observational and gridded monthly summary products, which offer an unparalleled level of archival and statistical detail, were offered to the research community. These products have been periodically updated and enhanced, with the period of record now covering 1784-1997. To date, the data have been the basis for more than 500 published papers (up to 60 a month in American Meteorological Society Journals for recent years).

In 2001, a major milestone for COADS was the release of higher quality data and products that extend from 1997 back to 1784. Our most recent efforts concentrated on the period prior to 1950, requiring exceptional efforts in data archaeology to locate and digitize millions of historical ship records from US and international archives that were never previously available in digital form. This also required extensive cooperation with a host of international partners, including China, Germany, India, Japan, the Netherlands, Russia, and the United Kingdom. Major input data sources for the pre-1950 period are detailed in Table 7.4.

Final observational and statistical products based on these and other data were completed in early 2001, comprising COADS Release 1c (1784-1949). Similar updates to more contemporary periods, Releases 1b (1950-1979) and 1a (1980-1997), were finished during 1996-1997. Thus upon completion of Release 1c, the original Release 1 (1854-1979) data were fully replaced by a consistent set of data and metadata products covering the extended period 1784-1997, with many additions of new and improved data. Web-based capabilities are now under development for subsetting in space and time of the basic 1784-1997 observations and statistics into easily used ASCII formats. When these new capabilities are finalized, COADS Release 2 will be considered complete.

Increases in the number of observations for the pre-1950 period due to new data are illustrated in Fig. 7.7. The two panels show the number of observations prior to 1950 previously available in COADS Release 1, plus the new observations recently added. The major contribution of the Maury Collection (left panel) towards extending the start of COADS prior to 1854 is clearly evident. It should be noted, however, that instrumental data are sparse prior to 1854 and most of these observations are wind estimates from sailing ships. Similarly, the right panel shows the importance of additions from the UK MDB, Kobe and US Merchant Marine Collections in the first half of the 20th century.

The increase in SLP observations between Release 1 and Release 1c is dramatic especially in the 19th century (Fig. 7.8). Much of the Release 1 data prior to about 1880 were from a "Dutch" source (possibly of international origin), in which pressure was available among supplemental data but not adjusted for gravity. These SLP observations have been adjusted for gravity and made available for the first time in Release 1c. We believe that these and other important increases in the numbers of historic observations have significantly improved COADS coverage, providing a good basis for future planned improvements.

A "Workshop on Advances in the Use of Historical Marine Climate Data" will be hosted by CDC 18-21 September 2001 in Boulder, Colorado, USA. The workshop, organized by NOAA, the UK Met Office and the Japan Meteorological Agency, and sponsored by the Global Climate Observing System (GCOS) and WMO, will build on the blend of the US Comprehensive Ocean-Atmosphere Data Set (COADS), with the UK Met Office MDB, plus with newly digitized data in the US and from other international partners. The blended product, encompassing 1784-1997, will provide the climate research community with an unprecedented assembly of in situ marine data.

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