The data sets to be constructed will comprise temperature, precipitation (and precipitation-related variables such as drought indices), atmospheric circulation (sea level pressure and geopotential height fields) and important atmospheric circulation indices (e.g., the North Atlantic Oscillation, the Euro-Siberian Oscillation, ENSO), covering the last 500 years. They will encompass a range of spatial scales (from local site, through sub-continental averages and, for temperature, hemispheric mean) and different temporal integration (discrete representation of interannual, decadal, and century time scales).
There is a wealth of long, good quality instrumental climate records, documentary data, and high-resolution and well-dated palaeoclimate data in Europe particularly, but also recently produced in many other Northern Hemisphere locations. Because they derive from different research projects, different laboratories, and different disciplines, very many of these have never been brought together. The opportunity is now available to do this and provide a major improvement over the last published compendium of similar data produced by Mann et al. in 1998. This workpackage will provide a major enhancement of our capability to explore and redefine the nature of natural climate variability for several centuries, both before and during the period of extensive observational climate records. We will assemble many published and many new/unpublished documentary climate records and high-quality palaeoclimate records from Europe and across the Northern Hemisphere within a timeframe of the last 500 years. In specific cases (e.g., for many tree-ring-derived variables), the palaeodata will be reprocessed so as to correct variance bias associated with time-dependent sample replication at individual collection sites; to decompose the data into selected spectral (i.e. period) bands with their associated statistical error; and to extract longer time scale (multi-decadal to century) variance based on a recently published technique not as yet applied at the small regional scale or to the vast majority of the tree-ring data. These proxy data will be climatically screened, by comparison with climate data, to identify appropriate climate variables with which to calibrate the palaeorecords in order to provide optimal seasonal and annual mean climate estimates. A combination of different regression and neural network techniques will be used. The derived prediction estimates will be rigorously validated (using reserved independent predictand data) and reconstruction uncertainty will be calculated and expressed with regard to changes in both time and time-scale. Where necessary, the calibration will be carried out at different timescales (i.e. annual-decadal; decadal-multidecadal; multidecadal-century) in order to better exploit the various sensitivities of the records and to allow cross comparison and appropriate amalgamation of the resulting data.
Very extensive collections of high-resolution tree-ring data (annual ring-width and ring-density measurements) will be amalgamated for the first time. These include many data from northern Europe, the Alps, the Pyrenees, North Africa, Spain, Italy, North America, Russia and China. In different regions, these data provide very good evidence of different climate parameters: summer temperature variability; summer drought; winter precipitation, all continuous and seasonally resolved. Many additional tree-ring data, including numerous strongly drought sensitive chronologies from western and eastern North America and Mexico will also be available to the project.
In addition to the high-resolution tree-ring data, selected additional records (some published, some uncalibrated, some with lower temporal resolution) will be used to derive corroborative evidence about multi-decadal and longer time scale variability of climate: these include ice-core accumulation and chemical isotope series; chironomid and diatom faunal records; speleothem data and peat compositional and accumulation records, and borehole temperatures. To improve existing ENSO reconstructions, a small subcontract will be let to an internationally-recognised expert on tropical corals to provide an up-to-date set of temperature sensitive Pacific coral records that are 100 to 300 (or more) years in length.
We have assembled a consortium with unique access to the latest climate data, the necessary documentary archives and the full range of palaeoclimate proxies, and with the methodological expertise to transform these data into homogeneous climate data sets that be compared with the different model outputs. Six partners will participate in this workpackage, contributing to all deliverables. Responsibility for certain tasks/regions will, however, be allocated to individual partners. Partners 1, 6 and 7 will lead the assembly of the necessary data sets; partners 6 and 7 will reconstruct European climate; partner 1 will reconstruct temperatures across the Northern Hemisphere; partners 1, 2 and 3 will reconstruct tropical Pacific (ENSO) variability; partners 5 and 7 will reconstruct atmospheric circulation variables; and partners 1, 5, 6 and 7 will analyse all reconstructed climate data sets.