Integrated Earth System Model: Formulation and Functionality
Understanding the future pattern and scale of climate change requires an understanding of how the human systems that drive climate change will evolve. However, human systems are vulnerable to and will adapt and respond to a changing climate. Changes in land productivity, water availability, or demand for heating and cooling services could significantly alter the nature of human resource management and therefore feed back to the drivers of climate change itself. Human and Earth systems co-evolve, yet the modeling tools used to project the behavior of these systems into the future typically treat them as independent processes. As a result, the magnitude and nature of such interactions are not well understood.
In a recent study funded by the Department of Energy’s Office of Science, a team of scientists from three national laboratories—Lawrence Berkeley, Pacific Northwest, and Oak Ridge national laboratories—have combined efforts to create a new integrated Earth system model (iESM). The iESM merges the human system components of an integrated assessment model and the physical, hydrological, ecological, and biogeochemical components of an Earth system model. This unified software framework is designed with flexibility and extensibility in mind. It permits the component models to be operated and developed separately, or to be run together in a coupled mode designed to probe interactions among them. The study documents the structure and rationale behind the iESM coupling framework and demonstrates its ability to reproduce one-way coupling from the integrated assessment model to the Earth system model that was previously conducted in an offline mode as part of the 5th Coupled Model Intercomparison (CMIP5) effort. The iESM also reproduces offline model output from individual model components to within machine precision.
The iESM, which will soon be released to the global climate research community, represents a major new model capability that permits the exploration of process-level interactions among human and Earth systems that were previously not represented in the existing suite of computational tools and procedures. While the initial version of the iESM focuses on carbon cycle interactions, the extensible nature of the software framework ensures that more complex interactions among human and Earth systems are able to be represented as well. Planned extensions include human emissions of short-lived climate forcers, climate impacts on human energy systems, and two-way interactions between climate and managed water systems.
Collins, W. D., A. P. Craig, J. E. Truesdale, A. V. Di Vittorio, A. D. Jones, B. Bond-Lamberty, K. V. Calvin, J. A. Edmonds, S. H. Kim, A. M. Thomson, P. Patel, Y. Zhou, J. Mao, X. Shi, P. E. Thornton, L. P. Chini, and G. C. Hurtt. 2015. “The Integrated Earth System Model (iESM) Version 1: Formulation and Functionality,” Geoscientific Model Development 8, 2203–19. DOI: 10.5194/gmd-8-2203-2015.