Ship logs
Starting with the Voyages of Discovery in the 1500s and transitioning into global commerce in the 1600s, European merchant and naval vessels regularly recorded weather information, including precipitation, atmospheric conditions, sea ice extent, and sea surface temperature (31). These records contain large numbers of observations across the global oceans and are of great potential value. Several international projects, such as the Climatological Database for the World’s Oceans (CLIWOC) and the Recovery of Logbooks and International Marine Data (RECLAIM), have digitized thousands of shipboard logbooks. Most of these records are now stored in the International Comprehensive Ocean-Atmosphere Data Set (ICOADS), providing surface marine data from as early as 1662 (32, 44). Together, these programs extracted millions of observations on sea surface temperature, sea level pressure, wind force, atmospheric circulation indices, and weather conditions (32, 44, 45). The application of these logbooks has so far included reconstructions of sea ice conditions in the Arctic (33, 34), understanding baseline ice and snow cover thickness in the Antarctic (46), and knowledge of historical hurricanes and monsoons (32).
However, investigations have also revealed data inconsistencies due to variations in observational methods across time and between ships (45). Early ship observations primarily consisted of subjective meteorological descriptions. The Beaufort wind scale was not commonly used until the 1840s, and instrumental data did not become widespread until barometer and thermometer reporting practices were standardized in 1853 (45). As a result, digitizing subjective records remains extremely labor-intensive and requires deciphering archaic terminology across numerous languages. Despite these limitations, logbooks may provide critical observations that predate modern ocean observations. With extensive collections of logbooks still undigitized, future efforts will continue to expand the range and usefulness of this climate record.
Landscape paintings
Landscape paintings also provide snapshots of the natural world before modern instrumental records, and recent analysis has illustrated their utility in reconstructing past environments (20, 25, 26). Many paintings, especially from artists with topographical landscape training, display consistent and accurate observations of surface conditions, vegetation, species, and habitat (20, 24, 25).
Researchers have also identified reliable representations of cloud formation, weather conditions, and atmospheric phenomena, which can be used to draw inferences about long-term changes (47, 48). For example, impressionist paintings in London and Paris over the 19th century accurately captured changes to the optical environment due to anthropogenic aerosol emissions, providing evidence for historical trends in air pollution before quantitative measurements began (49). In another example, the color of snow, ice, and watercolor in polar paintings reveal information about glaciers' reflectance and health (50). Yet, analyses also indicate that some paintings do not depict the landscape entirely faithfully (47), overrepresent certain climatic conditions (26), or romanticize natural features like fjords and glaciers (50). Although more work is needed to assess how art can inform quantitative science, paintings may provide critical insights into ecosystems, land use, and climate changes through the centuries.
Business and personal records
Archival records and oral knowledge have also been used to great scientific value. For example, observations from old diaries have been used to characterize the vegetation and landscape of the Mexican Bajío in the 16th century (51, 52), to track the first arrivals of migrating birds (2, 35, 36), and to reconstruct changes in spring mean temperatures using phenological data deduced from cherry blossom records and viewing parties in Japan (53).
Many historical records also provide continuous environmental records over significant periods. For instance, the high demand for timber for shipbuilding worldwide led to detailed national records and surveys of trees, mainly oak, which could be used to assess ecological forest changes (54, 55). Similarly, centuries of commercial fishery catch data provide insights into fish population abundances and shifts in aquatic ecosystems (42, 56). Beyond these written sources, ethical integration of Indigenous community knowledge provides a baseline for understanding regional ecosystems across scales (57, 58).
Integrating archaeology and paleoclimatology proxies
Finally, archeological and paleoclimate studies are critical in understanding ancient ecosystem structure, human history, and responses to environmental change. Archeological research on prehistoric coastal settlements has provided evidence of anthropogenic influence on marine ecosystems, improving the accuracy of baselines for fisheries management (56, 59). Historical trends in crop cultivation and forestry can be supplemented with studies of tree ring density to determine weather and climate controls on growth. (7, 12)
Paleoclimate methods provide excellent proxy data for precipitation, water availability, humidity, and seasonal temperatures (8, 60–62). Combined with historical documentation, this data can reveal vital insights into the impact of the climate on ancient societies. Studies have shown that during wet phases, the Maya experienced rapid growth, while multi-decadal droughts corresponded with social instability, depopulation, and collapse (60, 61, 63, 64). Similarly, the failure of Norse colonies and Northern European communities often coincided with a prolonged period of low temperatures (12, 62, 65–67), or sea level rise (68), and the Mongol Empire's expansion followed the spread of steppe grassland after the wet conditions of the Little Ice Age (8).
Applying these non-traditional data to the existing paleo and modern instrumental records considerably expands the baseline of documented climate conditions. To continue to expand the breadth of records available, identifying potential non-traditional records and integrating them with modern tools and paleo data will prove essential.