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Nachrichten, Termine, Experten
Historical logs from ships involved in the transatlantic slave trade also contain information about past climate conditions. Two climate researchers from the Max Planck Institute for Meteorology and a climate historian from Bielefeld University have joined forces to tap into this unusual data source to study the Intertropical Convergence Zone. The Volkswagen Foundation is supporting this innovative project, called "DOLDRUMS", with 1.3 million Euros.
This is a mutual press release by the Max Planck Institute for Meteorology and Bielefeld University.
About one-third of the Earth's precipitation falls in a narrow band of rain within the tropics, known as the Intertropical Convergence Zone (ITCZ). As the climate changes, its location, width and strength are predicted to change as well, which could impact the water supply for hundreds of millions of people. Reliably making such predictions requires a solid understanding of past changes. However, data is scarce. That is why two climate researchers at the Max Planck Institute for Meteorology (MPI-M) and a climate historian at Bielefeld University joined forces to investigate whether information about past changes in the ITCZ can be revealed from historical ship logs. The Volkswagen Foundation is funding the “DOLDRUMS” (Deciphering OLD ship Records to Understand the Maritime Structure of the Atlantic Intertropical Convergence Zone) project as a pioneering research initiative with the maximum grant of 1.3 million euros. The project will start in October 2025 and will run for four years.
“We are delighted that we have been successful with this somewhat risky but highly innovative project proposal,” says MPI-M researcher Claudia Timmreck. “We are expanding the range of methods available for reconstructing past climatic changes and, in doing so, are also learning something about the future.” Until now, it has been difficult to look into the past of the ITCZ since weather records mainly reflect the ITCZ through increased rainfall over land, even though it lies mostly over the ocean and is better characterized by surface winds. For example, climate archives such as speleothems (stalagmites and stalactites) or sediment deposits provide information about precipitation over land or near the coast. While surface winds over the oceans may have left no mark in natural archives, DOLDRUMS searches for their traces in human history: in logbooks from sailing ships, mainly from the transatlantic slave trade, which forcibly displaced millions of people from Africa to the Americas and the Caribbean between the 16th and 19th centuries.
Routes and revolts
When crossing the ITCZ, ships were exposed to thunderstorms, but sometimes also to almost complete windless calms. Being stranded in these regions, known as doldrums, could prolong a sea voyage by days or weeks. Therefore, the shipping routes themselves are likely to contain information about the winds and thus the ITCZ. In addition, there are notes on weather observations and human behavior. “The weather at sea had a major impact on living conditions on board the ships,” says Eleonora Rohland from Bielefeld University. “One hypothesis is that the nerve-wracking period of being stuck in the doldrums led to slave and crew mutinies because drinking water and food became scarce.” Reports of such situations could therefore also provide indirect clues about the weather conditions.
Virtual ships in a storm-resolving model
The researchers will interpret the ship log data with the help of the storm-resolving model ICON. “We want to establish the link between the large-scale wind conditions related to the ITCZ and the ship logs by sailing virtual ships through our climate simulations,” explains MPI-M researcher Julia Windmiller. The team then plans to look at the years 1783/84. At that time, the location of the ITCZ deviated from normal due to the eruption of an Icelandic volcano, providing an opportunity to test the hypothesis that external climate forcings are reflected in the ship log data. If successful, the researchers would have tapped into a new source of past weather data and a new way of testing climate theories. This would significantly improve not only the interpretation of past climate change, but also future climate projections.
With their unusual idea, the three researchers are literally venturing into uncharted waters. The Volkswagen Foundation's funding program “Pioneering Research – Exploring the Unknown Unknown” is designed for such risky research ideas. The selection process is highly competitive, with only a small percentage of all applications being approved.
Prof. Dr. Eleonora Rohland, University of Bielefeld: eleonora.rohland@uni-bielefeld.de
Dr. Claudia Timmreck, Max Planck Institute for Meteorology: claudia.timmreck@mpimet.mpg.de
Dr. Julia Windmiller, Max Planck Institute for Meteorology: julia.windmiller@mpimet.mpg.de
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