Abstract
Abstract. Narrative evidence contained within historical documents and inscriptions provides an important record of climate variability for periods prior to the onset of systematic meteorological data collection. A common approach used by historical climatologists to convert such qualitative information into continuous quantitative proxy data is through the generation of ordinal-scale climate indices. There is, however, considerable variability in the types of phenomena reconstructed using an index approach and the practice of index development in different parts of the world. This review, written by members of the PAGES (Past Global Changes) CRIAS working group – a collective of climate historians and historical climatologists researching Climate Reconstructions and Impacts from the Archives of Societies – provides the first global synthesis of the use of the index approach in climate reconstruction. We begin by summarising the range of studies that have used indices for climate reconstruction across six continents (Europe, Asia, Africa, the Americas, and Australia) as well as the world's oceans. We then outline the different methods by which indices are developed in each of these regions, including a discussion of the processes adopted to verify and calibrate index series, and the measures used to express confidence and uncertainty. We conclude with a series of recommendations to guide the development of future index-based climate reconstructions to maximise their effectiveness for use by climate modellers and in multiproxy climate reconstructions.
Highlights
Much of the effort of the palaeoclimatological community in recent decades has focused on understanding long-term changes in climate, typically at millennial, centennial, or at best sub-decadal to annual resolution
Three main categories of information appear in these sources that can be used independently or in combination for climate reconstruction: (i) early instrumental meteorological data; (ii) records of recurring physical and biological processes; and (iii) narrative descriptions of shortterm atmospheric processes and their impacts on environments and societies (Brönnimann et al, 2018)
Semi-quantitative nature, the two documentary sources are valuable for reconstructing past climate, especially for summer precipitation (Gong et al, 1983; Zhang and Liu, 1987; Zhang and Wang, 1989; Ge et al, 2011) and meiyu in different cities depending on the record length as described above
Summary
Much of the effort of the palaeoclimatological community in recent decades has focused on understanding long-term changes in climate, typically at millennial, centennial, or at best (in the case of dendroclimatology and palaeolimnology) sub-decadal to annual resolution. The main aims of this paper are as follows: (i) the provision of a global state-of-the-art review of the development and use of the index approach as applied to descriptive evidence in historical climate reconstruction; and (ii) identification of best practice for future investigations. There are instances in the literature where quantifiable data in documentary sources (e.g. sea-ice cover, phenological phenomena) and even instrumental meteorological data are converted to indices for climate reconstruction purposes This occurs mainly in studies where such data are integrated with narrative evidence to generate longer, more continuous and homogenous series with a consistent (monthly or seasonal) resolution. The number of instances where comparative analysis is possible is necessarily restricted by the limited number of studies that have undertaken either different approaches to index development for the same location or identical approaches for different regions
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