Spring-summer temperature reconstruction in western Norway 1734-2003: a data-synthesis approach

Abstract

A series of spring–summer (April–August) temperatures was reconstructed for the period 1734–1923 for western Norway based on multi-proxy data. For the period 1734–1842 the long-term variations were based on terminal moraines in front of two southern Norwegian glaciers, whereas the annual variations were based on grain-harvest data extracted from farmers’ diaries. For the period 1843–1867 the spring–summer temperatures were reconstructed solely from diaries overlapping instrumental observations. All the results were incorporated into one series for the period 1734–2003 to form the Vestlandet composite series. The reconstruction method using terminal-moraine sequences was tested against the modern instrumental Bergen series for the periods of moraine formations in front of the glaciers. The agreement with the instrumental series was good, with the mean difference for all periods being only 0.2°C. Analyses of decadal variations in western Norway revealed three periods of low spring–summer temperatures: around 1740, in the first decade of the 19th century, and in the 1830s. These periods are well known from historic records as periods of starvation, during which the use of bark bread became common.