Ensemble Kalman Inverse Parameter Estimation for Human and Nature Dynamics Two

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Since the widespread development of agriculture 10,000 years ago and particularly since the Industrial Revolution beginning in the 18th century, the coupled Earth and Human systems have experienced transformative change. The world's population and Gross Domestic Product have each increased by factors of at least eight in the last two centuries, powered by the intensive use of fossil energy and fossil water. This has had dramatic repercussions on the Earth system's stability, threatened by Human system activities such as habitat destruction, global warming, and depletion of Regenerating and Nonrenewable energy resources that increasingly alter environmental feedbacks.

To analyze these changes, we have developed the second generation of the Human and Nature Dynamics model, HANDY2. HANDY2 is designed to simulate the dynamics of energy resources and population over the Industrial era from 1700 to 2200, flexibly incorporating real-world observations of population and energy consumption in an expanded suite of mechanisms that track capital investment, labor force allocation, class mobility, and extraction and production technologies. The use of automated Ensemble Kalman Inversion (EnKI) estimation for HANDY2's parameters allows us to accurately capture the rapid 20th-century rise in the use of phytomass and fossil fuels, as well as the global enrichment of Elites that puts pressure on natural resources and Commoners. EnKI-derived HANDY2 ensembles project that current world policies may lead to a collapse in the world's population by 2200 caused by rapid depletion of resources. However, this collapse can be prevented by a combination of actions taken to support voluntary family planning, lower economic inequality, and most importantly, invest in the rapid expansion of Renewable energy extraction.