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Diaz, H.F., 1985

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Bibliographic Reference

Diaz, H.F., 1985, A comparison of twentieth century climatic anomalies in northern North America with reconstructed patterns of temperature and precipitation based on pollen and tree-ring data: University of Colorado, Boulder, Ph.D. dissertation, 255 p.

Abstract

The possibility of significant climatic changes over the next century or two resulting from anthropogenic modification of atmospheric composition and vegetative alterations makes it important to determine the ranges associated with different climatic regimes that have occurred during the present interglacial (in particular, the climate of the Middle-and Late-Holocene). The area of interest in this study comprises northern North America going from Alaska in the west to western Greenland in the east. The approach taken in this study was to use the modern observational record to identify the surface anomaly patterns and the associated midtropospheric circulation features characteristic of the principal modes of interannual variance in this region. These anomaly patterns were analysed within the context of the annual cycle by looking at seasonal variations and by comparison with the mean season-to-season changes. Principal component analysis was one major tool used to derive objectively the characteristic anomaly fields at both the surface and upper levels and to assess their temporal relationships. Other techniques included differencing various periods based on the integrated anomaly field and calculating field correlations between surface temperature and 700 mb heights. The surface patterns were contrasted to those derived using climate proxy data, such as variations in tree-ring growth and fossil pollen variations in order to infer plausible circulation regimes based on the degree of pattern similarity. Areas of consistent response during warm and/or cold periods operating at time scales varying from years to decades to centuries and finally to the order of millennia were identified and their existence was explained in terms of the possible redistribution (i.e. changes in the mean position and strength) of the planetary-scale waves in this region. The finding that the zone of high amplitude response is located approximately along the mean present-day boundary between arctic and Pacific or interior continental airstreams may help in the identification and monitoring of areas in northern North America where early detection of climatic changes due to increasing atmospheric CO2) concentrations is likely. Furthermore, by relating such responses to specific changes in the structure of the atmospheric circulation, we may have greater confidence that those surface changes are indeed related to hemispheric-scale variations, and not to natural variability of the climate system.

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