Climate models

To improve climate models, an international team turns to archaeological data


Climate modeling is forward-looking, its general intention to hypothesize what our planet might look like at a later date. Because Earth’s vegetation influences climate, climate models frequently include reconstructions of vegetation and are often validated by comparisons with the past. Yet such models tend to be oversimplified, obscuring or omitting how people affected the land and its cover.

The absence of such data has led to LandCover6k, a project now in its sixth year that includes more than 200 archaeologists, historians, geographers, paleoecologists and climate modelers from around the world.

Led by University of Pennsylvania archaeologists Kathleen Morrison Marco Madella from the Universitat Pompeu Fabra and Nicki Whitehouse from the University of Glasgow, with the data expertise of Penn landscape archaeologist Emily Hammer and others, LandCover6k’s goal is to aggregate archaeological and historical evidence land use systems from four time frames – 12,000 years ago, 6,000 years ago, 4,000 years ago and around 1500, in a single database that all the world can understand and use.

Understanding the human impact on Earth is more than looking at the vegetation of the past. It is also important to understand how humans used the land.


Archaeologist Kathleen Morrison

The project offers what researchers hope will become a tool to improve predictions about the planet’s future, and fill in the gaps in its past. “Understanding the human impact on Earth is not just about looking at the vegetation of the past. It is also important to understand how humans have used the land and in particular, the relationship between human use of land and vegetation, ”says Morrison.

Although current models of the Earth system suggest that human activity over the past 12,000 years has influenced regional and global climate, Madella says, “The models do not capture the diversity and intensity of human activities that have affected past land cover, nor capture carbon and water cycles. . “

Archeology provides important land use information that “helps reveal how humans affected past land cover on a global scale,” Whitehouse adds, “including crops and cultivated animals, how they were. cultivated and how much land was needed to feed the growing population. “

In a new PLOS ONE document, the team provides a detailed introduction to LandCover6k’s land use classification system and global database.

Create a common language, a system

Sharing such data first meant creating a common language that scientists from all disciplines could understand. It’s a bigger job than it looks, says Morrison. “Classification means putting hard edges on something. This is very difficult, as archaeologists are often much more comfortable with storytelling.

Partly due to a lack of common terminology, archaeologists did not attempt to aggregate and compare data on a global scale, which paleoecologists and project modelers had already done, adds. she. “We spent years consulting with colleagues around the world, discussing all the different types of land use, and developing a communication system – the same language, the same terminology – that could be used anywhere. . “

Over 200 archaeologists, historians, geographers, paleoecologists and climate modellers from around the world have contributed to LandCover6k, through workshops like the one presented here in Pondicherry, India, in March 2019. V. Selvakumar (foreground), professor at Tamil University, also visited Penn to complete land use mapping in southern India. (Pre-pandemic image: courtesy of Kathleen Morrison)

Because these categories have historically had different meanings depending on location, context, and period, some archaeologists were initially reluctant to commit to unique definitions for each. Hammer offers the concept of “agriculture” as an example. “The line between what is called ‘agriculture’ and what is considered small-scale food production by hunter-gatherers really varies across the world,” she says. So how could the terrain judge fairly when the actions of hunter-gatherers managing wild plant and animal resources have become “agricultural”?

Questions like these prompted the LandCover6k team to create a hierarchy within the classification system, with a top-level category capturing an idea in its broadest sense and several distinct subcategories descending from there. In the example of agriculture, the research team created a subgroup – low level food production – which could include the work of hunter-gatherers. The hope was to offer enough nuance for the archaeological community while still making the data accessible to climate modellers.

In addition to this flexible hierarchy and uniform terminology, the final classification has three other main characteristics. It is independent of scale and source, which means it captures the myriad of ways something can be studied. It “takes the point of view of the earth rather than of people”, as the researchers write in PLOS ONE, and it uses a consistent 8×8 kilometer grid scale. “It’s big enough, archaeologically speaking,” says Hammer, “but we made it so that one person didn’t draw something very small and another person very tall.”

Concrete examples

To show how the classification works, the researchers offer the example of the Middle East 6,000 years ago. This region, the area represented by modern Iraq, Syria, Jordan, Kuwait, Saudi Arabia, Qatar, Bahrain, United Arab Emirates, Oman and Yemen, was home to some of the world’s earliest agriculture. Using the new classification and the new database, project participants constructed a regional land use map, despite the availability of data which differs from place to place.

“Mesopotamia has been studied since the mid-19th century, so there is a lot of data and syntheses to draw on,” explains Hammer. “Arabia has not been so well studied. There are only a few data points, especially for this period, and due to climatic events, the data is even scarcer than for other periods. We wanted to illustrate the approach you would take in a situation where you have a lot of data versus a place with just a little. The new Middle Eastern land map is a proof of concept for the project, showing the contrast between the sedentary farms of Mesopotamia and the more sparse lands of Arabia.

Researchers don’t see information gaps, like those in Arabia, as problematic. Rather because the land use database also records the coverage and data quality, it can highlight areas that need more research. “Humans have transformed landscapes for thousands of years,” says Morrison. “But we can’t just say that. We have to demonstrate it.

And that’s exactly what LandCover6k aims to do, merging what archaeologists have gleaned about human land use at different times and places into a single database accessible to climate modellers – and some for the others. “This project is really about translating what we do,” says Hammer, “not only about standardizing terminology so that we can speak globally, but also about weaving in stories from the past. “

united states map

The final classification uses an 8×8 kilometer grid scale, which is large from an archaeological point of view but which allows for consistency. The four maps here show the effect of grid size on the visibility of the data. (Image: Chad Hill, posted in PLOS ONE)

Emilie Marteau is a lecturer in digital humanities and in archeology and anthropology of the ancient world in the Department of Languages ​​and Civilizations of the Near East in the School of Arts and Sciences to University of Pennsylvania.

Marco madeleine is ICREA professor-researcher in environmental archeology at the Department of Human Sciences of Pompeu Fabra University and coordinator of the Culture and socio-ecological dynamics research group.

Kathleen morrison is Professor Sally and Alvin V. Shoemaker and President of the Department of Anthropology in the School of Arts and Sciences to University of Pennsylvania and curator of the Asian section of the Penn Museum.

Nicki whitehouse is a lecturer in archaeological sciences at School of Humanities to Glasgow university and professor of human-environment systems at the Plymouth University.

LandCover6k is a Past Global Changes (PAGES) working group, part of Future Earth, an international community of sustainability scientists. Funding came from Marshal’s office at the University of Pennsylvania, Universitat Pompeu Fabra, PAGES, and the International Union for Quaternary Research. Austin Chad Hill and Jennifer bates, postdoctoral fellows in the Department of Anthropology to University of Pennsylvania, also contributed to research.


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