I discovered a farm's diary when I began my master's thesis in historical climatology. After a tip about a historic source - a farm diary that existed in Hamar, Hedmark County in eastern Norway - I could start my thesis. These diaries contained weather and climate information far back in time (around 1750 AD). This was unique for Norway, since we were a peasant country, and few in Norway could write at that time.
The diary starts on 17 May 1749 with the following sentence: "I first began Plowing out in the field, because snow had lain long and soil was not dry." It was a late date for the first plowing in this area of Norway. The norm for first plowing is in mid-April. The first diary was written by Major General Peder von Todderud (1691-1772) and this starts a long farm and diary writing tradition. While Todderud was of a farming family, he was also linked to the military and could therefore write. I gradually discovered that there was a tremendous amount weather and climate information in these diaries, written in gothic letters. After Todderud died, his son Major Barthold Henrick Todderud (1724-1805) inherited the farm and the diary writing in 1772. The diary writing increases in quantity, especially about the weather. In 1805 his grandson Captain Eilert Ditlef Todderud (1773-1738) inherited the farm and diary writing. The amount of diary writing increased still more. Eilert wrote his diary until 1835. Then the Todderud family diaries ended, and 1835 is therefore the last year of my climatic history.
Documentary data are useful for constructing long, high-resolution time series from historical times to the present. These data can provide valuable information on the paleoclimate, thereby complementing and supplementing instrumental measurements. In this thesis, documentary data in the form of diaries from the Aker farm in Hamar, Hedmark county, eastern Norway are used to reconstruct the climate there from 1749–1835, a period during the last part of the so-called Little Ice Age (LIA) and an extension and complementation of Oslo time series from 1816.
An index method is developed and used to quantify these qualitative climate-proxy observations in order to reconstruct temperatures and precipitation annually and for winter and summer, 1749–1835. These annually and seasonally resolved reconstructions are termed the “Åker series”. In addition, sub-seasonal resolution reconstructions of temperature, precipitation, wind and cloud cover for the period 1805–1835 are developed. These reconstructions use a method that keeps the climate observations in qualitative form.
The result from the climate reconstruction implies conditions consistent with the climate of the LIA. The climate in 1749–1835 was apparently both colder and wetter than today, and the year 1812 was especially cold. Due to cold and wetter weather, in this period farmers sometimes suffered hardships owing to bad harvests.
Elin Lundstad is a climate researcher with the climate division of the Norwegian Meteorological Institute.