Climate History and Climate Reconstruction in the Global South

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This article provides additional commentary on a recently published article written by a historian, two climatologists, and two undergraduate research assistants in a climatology journal: Philip Gooding, Melissa J. Lazenby, Michael R. Frogley, Cecile Dai, and Wenqi Su, “Documents, reanalysis, and global circulation models: a new method for reconstructing historical climate focusing on present-day inland Tanzania, 1856–1890,” Climate of the Past, 20, 12 (2024), 2701-18.

For related articles and TV interviews, see: City News, CTV News, and Noovo Info, as well as English– and French-language press releases from McGill University.

One of the under-reported features of global climate injustice is that climate models are at their most uncertain when modelling climate over many of the most climate-vulnerable regions in the world. To be clear, climate modellers are able to model how global warming will affect climate on a global scale. However, the data on which they do so is at its thinnest and most historically shallow over much of the Global South, a result of the macro-region’s neglect by the global scientific community during and after colonialism. This has contributed to a great deal of uncertainty in modelled projections about, for example, how global warming will affect different regions’ rainfall. Historical climatologists are thus continually trying to improve the historical baselines on which climate modellers can project future climatic conditions under different global warming scenarios.

Locations of natural proxy sources, including tree rings, ice cores, etc., that are integrated into the Paleo-Hydrodynamics Data Assimilation Product to estimate climatic conditions on annual (Apr.-Mar.) and seasonal (Dec.-Feb. and Jun-Aug.) scales in the years 0-2000 CE.
Figure 1: Locations of natural proxy sources, including tree rings, ice cores, etc., that are integrated into the Paleo-Hydrodynamics Data Assimilation Product to estimate climatic conditions on annual (Apr.-Mar.) and seasonal (Dec.-Feb. and Jun-Aug.) scales in the years 0-2000 CE. Note, the absence of in-region data in much of the Global South, especially compared to Europe and North America. This owes itself to a lack of tree ring and other research into natural proxy sources in many of these regions. We argue that historical documents can help to fill these gaps.

Our article, “Documents, reanalysis, and global circulation models,” represents an attempt to improve such historical baselines. It does so by integrating not just evidence from the atmosphere and the natural world (such as from tree rings), but also qualitative descriptions held in historical documents. The results speak to the need for interdisciplinary solutions from both the humanities and natural sciences to understand regional climates, especially in the Global South, and to the important role that historians can have when working with climate modellers and other climatologists in this context. Historical sources and methods have a significant role to play in improving baselines on which future climatic conditions can be modelled.

The article itself reconstructs seasonal rainfall conditions in three historically significant locations in inland present-day Tanzania in 1856–1890. These years cover the final circa thirty years before the Scramble for Africa. The documentary source base for the period is dominated by the letters and publications of early European imperialists and missionaries. Although under-utilized by climate modellers, historical geographers have acknowledged that such documents hold a wealth of useful descriptions and data about weather. In so doing, they have made several documentary-derived time-series of rainfall variability, including in eastern Africa and elsewhere in the Global South.

What they have yet to do—and what “Documents, reanalysis, and global circulation models” does for the first time—is to integrate such time-series with evidence from existing global climate reconstructions. Such reconstructions model climatic conditions based on data from the atmosphere and from natural proxy sources, such as tree rings—the latter studies being absent from existing climatological investigations in Tanzania and in many other regions in the Global South (see figure 1). The result of our efforts is a novel reconstruction of seasonal rainfall variability in Tanzania that accounts for evidence from the region (documents), evidence from the wider world (e.g. tree rings in other regions), and evidence from the atmosphere (e.g. well-mixed greenhouse gases).

One of our core arguments is that interpreting historical documents and outputs from global climate reconstructions collectively enhances the value of both. Missionary and imperial letters are, in many ways, highly problematic. Their authors reported on weather through highly racialized paradigms rooted in climatic determinism. They were also regularly sensationalist in their reports about extreme weather. Indeed, one of our major findings was that when missionaries reported on drought-driven famines, trends towards deficient rainfall may have set in before the missionaries reported on it, according to the climate models we consulted. Meanwhile, analysis of European reports allows for an evaluation of existing climate models against data that was collected in the region, which is currently absent from their underlying data.

This, then, represents a call for further research along the lines that we have laid out. As readers of the article in Climate of the Past will discover, we have created a methodology through which historians and climatologists/climate modellers can work together, integrating their sources and methodologies, to create time-series of climate variability that are rooted in both the humanities and natural sciences. This kind of interdisciplinary work is essential for creating long-term historical baselines on which to model future climatic changes under global warming. This is especially important for many regions of the Global South, for which scientific knowledge about regional climatic systems remains highly uncertain and based on historically shallow data. We have shown that historical sources, such as the missionary and imperial documents we consulted, have the capacity to enhance climate models. We hope that other historians and climatologists will do likewise moving forwards.

Feature Image: Figure 7: Time series representing integrated and weighted precipitation anomalies for all locales. From Philip Gooding, Melissa J. Lazenby, Michael R. Frogley, Cecile Dai, and Wenqi Su, “Documents, reanalysis, and global circulation models: a new method for reconstructing historical climate focusing on present-day inland Tanzania, 1856–1890,” Climate of the Past, 20, 12 (2024), 2701-18.

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