Humanity is now a geological force. Industries belch greenhouse gases into the sky; dams reroute waterways. People are changing major planetary cycles in the atmosphere, cryosphere, and ocean. These complex, multi-faceted effects have feedbacks that, in turn, affect society. And this presents a problem for researchers looking to understand and predict how Earth is changing in the midst of the Anthropocene: How do we factor our significant and ever-changing impacts and interactions into models of the planet’s biogeochemical cycling and other systems? While models simulating physical, chemical, and ecological cycles, as well as models simulating social dynamics, already exist in the literature, the two types typically aren’t combined.
Drawing on feedback from dozens of scientists across disciplines, a recent paper in Earth System Dynamics offers a conceptual framework to identify and combine these models from across the physical and social sciences. It introduces three broad organizing categories to classify models: the “biophysical,” “socio-metabolic,” and “socio-cultural.” By offering researchers a common starting point to thoughtfully combine their models, the researchers hope to offer better ways to study interactions and feedbacks between biophysical and social processes. A separate companion paper applied the framework to software in 2020 to build a simple example model. “It’s really a new way of looking at how models for the Anthropocene can be constructed,” says lead author Jonathan Donges, an Earth system scientist at the Potsdam Institute for Climate Impact Research, or PIK, in Germany. “A framework of that kind to my knowledge didn’t exist before.”
Since the 1980s, state-of-the-art Earth system models have included chemical, physical, and ecological inputs and outputs. But they generally don’t explicitly account for human social factors (See also Core Concept: Integrated assessment climate policy models have proven useful, with caveats). But now, the social dynamics of human societies, especially how we make decisions, as well as feedbacks among those decisions and biogeochemical cycles, must also be included.
“We usually have models of parts of human behavior, like economic models, or we have models of the climate system,” explains senior coauthor Wolfgang Lucht at PIK. “But what if these two are coupled? We don’t really have models for that.” To help devise ways to merge these approaches by bringing together various independent lines of research, Lucht hosted a series of 3-day interdisciplinary workshops in 2014, 2015, and 2017, including 30 to 40 scientists each time. Based on this and prior work, the coauthors identified three broad themes that they argue, when combined, capture the whole Earth system, including human impacts and feedbacks: the “biophysical,” the “socio-metabolic,” and the “socio-cultural.”
The biophysical, Donges says, describes planetary processes themselves, separate from human impacts. The socio-metabolic encompasses all areas where humans interact with nature and change it, such as in agriculture and dams. And the socio-cultural includes aspects of society, such as opinion formation, social network formation, and political decision-making, which can all be modeled in computer simulations.
Next the authors built a simple example that combined all three themes and their interactions. They described a world in which climate change alters some governments’ relative interest in their short-term versus long-term welfare, ultimately affecting global emissions and global atmospheric carbon. While simplistic—built using two differential equations (one for government long-term versus short-term thinking, and one for atmospheric carbon)—the model demonstrated how one might build in social choices and social-ecological feedbacks through each government’s choices.
In a companion paper, Donges and coauthors used this thematic framework to lay out design principles for models containing biophysical, socio-metabolic, and socio-cultural processes. Rather than building such models from scratch, they recommend combining existing models of both social and physical processes—for example human opinion formation (sociocultural) and the carbon cycle (biophysical). Models combining these processes could eventually help answer questions such as how political polarization in society affects future climate policy, Donges says.
Ultimately, Earth system models that take humans into account could inform biosphere resilience and environmental policy, says sustainability scientist Carl Folke, director of the Beijer Institute of Ecological Economics in Sweden. In this paper, he says, Donges and colleagues made initial strides toward integrating people and the planet as intertwined social-ecological systems. This framework to couple nature–human systems quantitatively is “simple by design; but it’s a great first step,” notes Earth system modeler Yangyang Xu at Texas A&M University in College Station. This week, Xu and collaborators published another model framework that attempts to integrate human systems and natural systems, specifically in the context of energy use and climate change. Coauthor Veerabhadran Ramanathan, an atmospheric and climate scientist at the University of California, San Diego, in La Jolla says that although the two studies have different emphases, they both “reveal the importance of factoring in human–nature interactions in designing climate solutions and actions.”
Looking ahead, Lucht says, the goal is to build more complex models accounting for both biophysical and social processes, and the interactions and feedbacks between them. Such models could eventually demonstrate, for example, which human behaviors lead to the least detrimental environmental impacts, or under which conditions collective human behaviors can lead to environmental sustainability, rather than collapse. “We’re interested, for example, in a model with a simple climate and economic and sociocultural system, that produces emissions and so on, and where people vote and form opinions about climate policy,” Donges says. “Then we think about how they interact and influence each other.”
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