April 2009

Benefits for climate monitoring and assessment of data rescue activities

by Phil Jones*

Source: WMO statement on the status of the global climate in 2008 (WMO-No. 1039)

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In most regions of the world there are longer instrumental records than apparent in a cursory search of the website or archives of a National Meteorological and Hydrological Service (NMHS). In most cases this results from the NMHS not yet having digitized all the meteorological data in its archives. In many cases the records pre-date the founding of the Service, whereas in others they pre-date the founding of the country. It is important that these early records, which were often taken with meticulous care by early scientists and medical doctors, be digitized and made available for climatological use. These early records are generally to be found in national or learned society archives, sometimes located in the archives of an earlier colonial power. Present-day scientists owe their forebears much gratitude for taking these early measurements with meticulous care and diligence. Given this effort, it would be a shame if they were left to collect more dust in an archive.

Extending climatic series brings a number of scientific benefits, both to the NMHS and to the climatological research community in the country and in the region. The primary benefit is that the longer records enable trends and other analyses to be more extensive, placing recent records and extremes in the longer context. Longer climatic series also provide instrumental data for more extensive calibration of natural and documentary proxies, both of which have the potential for extending the climatic history further back in time. Longer observational data provide better coverage (in both space and time) for extended reanalysis projects, planned to begin from the late nineteenth century. Lastly, longer records are useful for assessing impacts of climate change over more extensive time frames than just the recent past. The following two examples discuss the above for northern and western Europe. They illustrate what has been achieved through more extensive digital instrumental data.

Longer records for the assessment of proxy evidence

Longer climatic reconstructions require information from natural (for example, trees and ice cores) and documentary (written archives) proxy material. These proxy records must use instrumental records to calibrate the proxy source. In many regions, calibration is hampered by the lack of long instrumental records. In Europe, however, it is generally possible to assess the quality of possible reconstructions, especially the longer decadal-timescale details, for almost 200 years. The figure shows examples of such calibration exercises using a long instrumental record developed for northern Fennoscandia. Both proxy series show good replication of instrumental temperatures at the inter-annual and decadal timescales.

Comparison of instrumental and proxy records developed for northern Fennoscandia (using the instrumental temperature series for Haparanda, developed by Klingbjer and Moberg (2003), which extends back to 1800); top panel: April–May instrumental temperatures (red), estimated temperatures based on ice break-up dates (blue); bottom panel: June–August instrumental temperatures (red), calibrated temperatures based on tree-ring width and density data (green, from near Lake Torneträsk)

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Extensions of the North Atlantic Oscillation

The longest record of the winter North Atlantic Oscillation (NAO), back to 1820, has been derived by Jones and others (1997) based on pressure data from Gibraltar and Reykjavik. As the NAO is essentially a measure of the westerly wind strength over western Europe, two long well-located pressure records would provide a good surrogate for the more distant locations in Iceland and southern Iberia or the Azores. The two locations with the greatest potential length anywhere in the world are Paris and London. At both sites, near-continuous daily pressure records have been taken since the late seventeenth century. For Paris, a complete record has been developed back to 1677, missing only most of the years in the 1720s and 1730s. For London, the record is complete from 1692, missing only the years between 1717 and 1722. Despite these short gaps, a very useful approximation to the winter NAO has been developed back to 1692.

References

Jones, P.D., R. Jónsson, T and D. Wheeler, 1997:  Extension to the North Atlantic Oscillation using early instrumental pressure observations from Gibraltar and SW Iceland. International Journal of Climatology, 17:1433–1450.

Klingbjer, P. and A. Moberg, 2003: A composite monthly temperature record from Tornedalen in northern Sweden, 1802–2002, International Journal of Climatology, 23:1465–1494.

* Climatic Research Unit, School of Environmental Sciences, University of East Anglia, UK

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