Development of Temperature Indices for Scotland and Northern Ireland
Report No SR (99) 07 F
Feb 2000

The Centre for the Study of Environmental Change and Sustainability (CECS) at the University of Edinburgh was appointed in May 1999 by the Scottish and Northern Ireland Forum for Environmental Research (SNIFFER) to produce a report entitled "Development of Temperature Indices for Scotland and Northern Ireland". The work was carried out with sub-contractors from the Environmental Science Department at the University of Stirling; the Meteorological Office and the Marine Laboratory of the Fisheries Research Services.

The aims of the study were:

• To develop a set of long-term marine and terrestrial indices representative of the climates of Scotland and Northern Ireland.
• To compare and contrast any regional marine and terrestrial indices that might be developed.
• To compare and contrast the regional marine and terrestrial indices with other European and global indices.
• To provide a framework for the continued maintenance of the indices, such that they would become a first point of reference for those undertaking regional climate change studies in Scotland and Northern Ireland.

Three regional terrestrial indices were identified as being sufficiently climatically different to justify development: a Northern Ireland Index (NII), a Scottish Mainland Index (SMI) and a Scottish Islands Index (SII). Data for the indices were chosen on the basis of length of record, perceived quality of record and the provision of a climatically representative set of stations for the region in question. In the case of Northern Ireland, only a single suitable station was identified at Armagh. The Scottish Islands Index consisted of data from Stornoway and Lerwick, and the Scottish Mainland Index of data from Braemar, Dumfries, Edinburgh Royal Botanic Gardens, Paisley and Wick. Before calculating indices the data series were first checked for completeness. Where necessary they were regressed with other suitable series in order to fill gaps or extend the series. Homogeneity testing was undertaken in order to identify discontinuities in the records. These may be caused by changes in exposure, instrumentation or measurement techniques and were identified and corrected by comparison with other similar series. Final indices were produced as the unweighted monthly, seasonal and annual means of minimum, maximum and mean temperature for the candidate series. Limited data were available for the marine indices which were calculated for three areas that were considered as important indicators of ocean climate status. A West Coast Index, a Shelf Edge Index and a North Sea Index were produced using both data measured in-situ along ocean transects at multiple depths (except for the West Coast Index) and through use of a global 1° resolution long-term sea-surface temperature data set (GOSTA Plus).

A comparison of 30-year means of annual mean temperature between 1873-1902 and 1961-1990 demonstrated clearly that, although the amount of warming varied, the three SNIFFER terrestrial indices showed warming of between 0.11°C and 0.39°C - similar to both the Hansen global index and the Central England Temperature record. Most of this warming was found to result from an increase in the mean minimum temperature, rather than any significant change in the mean maximum temperature. The Shelf Edge (the only long-term marine index) showed warming of between 0.12°C and 0.29°C over the past century (depending on the use of in situ measurements or the global sea-surface temperature data set).

A set of temperature indices have been developed from 130-year terrestrial (1872-1998) and 100-year marine (1901-1999) records that are considered to be representative of Scotland and Northern Ireland. They indicate a warming trend of similar magnitude to other regional and global studies. The warming arises mostly from increases in the mean minimum temperature rather than significant changes in the mean maximum temperatures.

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