TREE-RING BASED RECONSTRUCTION OF SUMMER TEMPERATURES AT THE COLUMBIAICEFIELD, ALBERTA, CANADA, AD 1073-1983

April-August temperatures are reconstructed from maximum latewood dens ity and ring-width data for a tree-line site in the Canadian Rockies o f Alberta close to Athabasca Glacier. The chronology primarily utilize s Picea engelmannii with some Abies lasiocarpa snags. This reconstruct ion (AD 1073-1983) is the longest densitometrically based summer tempe rature record from boreal North America, Mean temperatures from 1101-1 900 were 0.71 degrees C below the 1961-1990 reference period and 0.33 degrees C below the 1891-1990 mean of the instrumental record. The col dest interval was the first half of the nineteenth century and the maj or cold intervals, c. 1200-1350, 1690s and the nineteenth century, coi ncide with local and regional periods of glacier expansion. Warmer per iods, c. 1350-1440 and in the present century, are also periods of hig her tree-line or tree-line advance at the site. The 1961-1990 referenc e period is clearly warmer than any equivalent-length period over the last 800 years. This record of summer warmth reinforces evidence of si gnificant warming at several high-latitude and high-latitude sites aro und the Northern Hemisphere in the late twentieth century. The reconst ruction also indicates that glacier advances of the 'Little Ice Age' i n the Rockies occurred during a period of fluctuating climatic conditi ons rather than a long period of sustained cold of several centuries d uration.