Historical weather data to prepare us for the climate of the future

27. June 2022

Historical weather data to prepare us for the climate of the future

Ship’s records with millions of weather observations from centuries of sailing under the Danish flag, logbooks and yellowed messages in a bottle with weather records provide important data for future climate research.



For several centuries, skippers and mates on Danish ships have kept a weather log on their voyages. The quiver and ink records are now being digitised to provide large data sets for today’s climate models.

The project is called ROPEWALK (Rescuing Old data with People’s Efforts: Weather and climate Archives from LogbooK records), which offers a unique source of data in that no comparable weather observations from other known sources exist from that time. The historical weather observations have never been used before and can provide a far better understanding of past weather and future climate change.

The project is a collaboration between the Danish National Archives and the Danish Meteorological Institute, made possible thanks to a generous grant of DKK 14.25 million from the A.P. Møller Foundation.

Ship records and logbooks provide knowledge about changes in weather conditions

The Danish National Archives has more than 700 shelf meters of ship records, logbooks and other maritime material from thousands of Danish ships dating as far back as 1675. A large part of the material comes from the Danish Navy, and there are large collections from the Royal Greenland Trading Department and the Royal Danish Academy of Sciences and Letters as well.

Archivist Adam Jon Kronegh from the Danish National Archives, who is managing the project in collaboration with the Danish Meteorological Institute, sees great value in the extensive records: “We owe the Danish sailors a big thank you, as the ship records are a treasure trove of knowledge about weather conditions over a long historical period. For example, the records detail weather conditions in the Øresund region and Arctic, especially in Greenland. The knowledge we gain from these historical sources is unique, both in terms of their uniformity and scope, and there has already been a lot of interest in using this data for climate research in Denmark and abroad.”

The weather of the past can be used in future climate research

The captains of the Danish ships were required to keep logbooks and ship records on their voyages and had to record everything that took place on board, as well as the specific weather conditions.

These maritime records therefore contain valuable information about pressure, wind, current, ice and temperature conditions. Today, each isolated observation can be ‘placed’ using an intelligent analysis method, allowing researchers to reconstruct weather conditions and obtain information about the climate of the past.

The data can also serve as the basis for models aimed at predicting climate change and in research.

Accessible to everyone

This unique climate data will be made available for free to Danish and international climate researchers as well as the general public.