European 6K Climate Reconstructions: Readme file ----------------------------------------------------------------------- NOAA Paleoclimatology Program and World Data Center A- Paleoclimatology ----------------------------------------------------------------------- NOTE: PLEASE CITE ORIGINAL REFERENCE WHEN USING THIS DATA!!!!! NAME OF DATA SET: European 6K Climate Reconstructions LAST UPDATE: 3/97 CONTRIBUTORS: Rachid Cheddadi, Ge Yu, Joel Guiot, Sandy Harrison & Colin Prentice IGBP PAGES/WDCA Data Contribution Series #: 97-006 SUGGESTED DATA CITATION: Cheddadi, R., et al, 1997, European Climate 6K Reconstruction. IGBP PAGES/World Data Center-A for Paleoclimatology Data Contribution Series # 97-006. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA. ORIGINAL REFERENCES: Guiot J, Harrison SP, Prentice IC (1993) Reconstruction of Holocene precipitation patterns in Europe using pollen and lake-level data. Quaternary Research 40: 139-149. Cheddadi, R. Yu, G. Guiot, J., Harrison, S.P. and Prentice, I.C. (1997): The climate of Europe 6000 years ago. Climate Dynamics, 13: 1-9. GEOGRAPHIC REGION: Europe PERIOD OF RECORD: 6000 yr BP LIST OF FILES: climat6k.dat, climate6k.readme DESCRIPTION: Latitude of grid points: 50N to 80N by step of 0.5 degrees Latitude of grid points: 10W to 35E by step of 0.5 degrees Variable plotted: Climate surface conditions over Europe Codes: P-E (annual Precipitation minus Evapotranspiration); GDD (Growing Degree Days above 5°C); Tc (mean Temperature of the Coldest month); ( (ratio of actual to equilibrium evapotranspiration). Data precision: These climatic variables are anomalies of the 6000 years BP values minus the present day values. The 6000 BP climatic data are inferred from 403 pollen sites and then interpolated for Europe using an artificial neural network. 93 unrestricted pollen sites have been used from the European pollen database. The area at east of 35°E and south of 50°N is lacking because of the scarce and uneven coverage. Data format: the file climat6k.dat is a text file containing: longitude,latitude,GDD,Tc,A,P-E The fields are separated by a comma Contact: Rachid Cheddadi - European Pollen Database Centre Universitaire d'Arles Place de la République 13200 Arles - France Tel: 04-90961818 / Fax: 04-90939803 email: epd@dialup.francenet.fr J. Guiot LBHP CNRS UA 1152 Faculté de St. Jérôme Boite 451 13397 Marseilles Cedex 20 Tel: 04-91288011 Fax: 04-91288668 email: joel.guiot@lbhp.u-3mrs.fr Abstract of the main paper: Palaeoclimates across Europe for 6000 yr BP were estimated from pollen data using the modern pollen analogue technique constrained with lake-level data. The constraint consists of restricting the set of modern pollen samples considered as analogues of the fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration (PE) is consistent with the regional change in moisture balance as indicated by lakes. An artificial neural network was used for the spatial interpolation of lake-level changes to the pollen sites, and for mapping palaeoclimate anomalies. The climate variables reconstructed were mean temperature of the coldest month (Tc), growing degree days above 5C (GDD), moisture availability expressed as the ratio of actual to equilibrium evapotranspiration (), and PE. The constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies, especially for PE. The reconstructions indicate clear spatial and seasonal patterns of Holocene climate change, which can provide a quantitative benchmark for the evaluation of palaeoclimate model simulations. Winter temperatures (Tc) were 1-3 K greater than present in the far N and NE of Europe, but 2-4 K less than present in the Mediterranean region. Summer warmth (GDD) was greater than present in NW Europe (by 400-800 K day at the highest elevations) and in the Alps, but > 400 K day less than present at lower elevations in S Europe. PE was 50-250 mm less than present in NW Europe and the Alps, but was 10-15% greater than present in S Europe and PE was 50-200 mm greater than present in S and E Europe. Brief description of the method: The technique used to translate pollen data into quantitative palaeoclimatic estimates is the modern analogue approach. The degree of analogy between modern and 6000 yr BP pollen assemblages was measured with chord distance. Lake status anomalies were estimated for the 403 sites with 6000 yr BP pollen data. The lake status anomalies are then compared with the reconstructed PE from pollen data. The modern pollen assemblages with (PE) values inconsistent with the lake-derived value of moisture index are rejected. The eight best constrained analogues are used to reconstruct the climatic variables. To correct the elevation-related bias in the climate reconstructions we recalculated anomalies relative to the reconstructed modern climates, instead of actual modern climates, for all pollen sites above 1000 m. The anomaly values were interpolated three-dimensionally using the Artificial Neural Network method, with input variables latitude, longitude and elevation. Data generation: 1996.