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140 and 141

Task 140 and 141

Earth Model-Human Model

Principal Investigator(s):

E. Kalnay


S. Motesharrei and Fang Zhou


R. Cahalan

Last Updated:

October 26, 2012 15:25:39

Description of Problem

Human population and consumption has grown significantly over the past few decades. The Earth’s natural resources were assumed to be practically infinite for the whole length of the history, but we are now realizing that they may be scarce. This has rung a bell for the policy makers, scientists, economists, and all other conscious individuals. Economic growth has reached an “uneconomic growth” phase. To cope with such issues, new fields of study like “ecological economics” are born. Several research groups around the globe have developed (mathematical) models to predict the future of human population and nature. Such models have helped scholars to understand and investigate possible scenarios for the future of life on our planet more thoroughly.

The most complete versions of such models incorporate population, climate, energy, and agriculture as main variables. However, some of these variables, like population, are taken as exogenous variables and therefore, the coupling between the variables is uni-directional. This means that, for example, increased population can affect climate by creating more pollution, but the climate change does not feed back on the population.

Scientific Objectives and Approach

We are developing a prototype Earth System Model (ESM) coupled with a Human model where all of the above-mentioned variables are fully coupled to each other. As a result, we do not need to import the values for any of the variables from external sources, e.g. United Nations population projections for the next 50 years. Instead, the model internally determines any of the variables, say population, in the coming decades based on the dynamical relations with the rest of the variables. When the prototype model is ready we will work with the Climate@Home team to post the model and allow many members of the public to test the impact of the model assumptions and parameters on the model behavior. Calibration of models is a fundamental issue, and we plan to apply the powerful tool of Local Ensemble Transform Kalman Filter (LETKF) to calibrate the parameters of the model to the past 40 years or so of observed data.


During the first three months of the project (Jan-Mar 2011), we developed a basic toy version of our model, with two variables, population and nature. Nature represents an aggregate of physical and natural resources. Although we could observe scenarios showing periods of growth and decay using that model, we were not content with the structure and possible outcomes. Kalnay and Motesharrei, together with Jorge Rivas (external collaborator from University of Minnesota), continued developing several versions of the model until Nov 2011. This latest version of the model, called HANDY (Human And Nature DYnamics), has population separated into two variables, Rich and Poor, as well as an additional variable, Wealth, which represents the accumulated physical wealth, i.e. consumable goods and products. Production is done by the Poor. Although the Rich does not work, it controls the Wealth.

We observed several interesting output scenarios of this minimal 4-variable model: steady-state equilibrium, overshoot followed by oscillatory approach to the carrying capacity, severe overshoot resulting in full collapse, and collapse after a long period of equilibrium. In Dec 2011, Motesharrei presented the above results for the first time at the AGU annual meeting in San Francisco, CA. He also presented the results at the Dynamics Days 2012 conference in Baltimore, MD, in Jan 2012.

In late Jan 2012, we also observed scenarios that explains the direct effect of high productivity per capita (long work hours) on unemployment. Motesharrei presented this new result together with the earlier results at the Weather and Chaos Group semester kick-off seminar on Feb 6, 2012, at the University of Maryland, College Park, MD. Kalnay also presented these results on Feb 14, 2012, at the Jet Propulsion Laboratory (JPL) in Pasadena, CA. We are currently preparing a manuscript of the results from HANDY for publication.

In summer of 2011, together with Jorge Rivas, Fernando Miralles (FIU), and Cortney Gustafson (visiting graduate student of Miralles from FIU), we developed a Human-Water model, INCOWA (Intermediate-Complexity Water model). We also created a simplified version of INCOWA, called SIWA (Simple Water model). INCOWA still needs further development. However, we were able to obtain some preliminary results from SIWA. We simulated effects of three different factors: pipeline leaks, water dispensing technology, and recycling capacity on sustaining the freshwater sources and supplies. We observed that there is a critical value for each parameter (interdependent with the value of the other two parameters) below which the lifetime of the supply can become very short. We are planning to present these results at the upcoming conferences and develop them for publication.

We also employed SIWA to study the causes of Famine in the country of Somalia. Gustafson represented results of that study at the AGU annual meeting in San Francisco, CA, in Dec 2011. Gustafson will be back in 2012 to continue her work with us on INCOWA.

Over past several months, we have submitted several proposals to various institutions and agencies. We have followed two major themes in these proposals:

1. Further development of HANDY by adding a population distribution and separating Nature into Renewable and Non-Renewable Sources. Kalnay and Motesharrei will be collaborating with Jorge Rivas, Victor Yakovenko (UMD, Physics Dept), and Matthias Ruth (UMD, Public Policy) for this project. A proposal was submitted to INET (The Institute for New Economic Thinking) which made it to the final round of the selection process, but did not win. A second proposal was submitted to SeSynC (Socio-Environmental Synthesis Center), currently under review.

2. Coupling the water model to a climate model and a river-routing module, and adding an economic module to the water model. Kalnay, Motesharrei, and Zhao will collaborate with Ning Zeng (UMD, AOSC), Rivas, Miralles, Gustafson, and Toon Haer (visiting Masters student from the Netherlands) in this project. Zhao has worked on running the UMD-ICTP Global Climate Model (GCM) in the North Africa region since his arrival in UMD in Aug 2011. He has also started development of a river-routing module to be coupled to the UMD-ICTP Earth System Model. He will complete this work and building and running the couple Human-Water-Climate model after finishing his qualifying courses and exams in June 2012.

We submitted a proposal to the Maryland Water Resources Research Center which was not awarded a grant. However, the Director of the center, Prof. Kaye Brubaker, supported redeveloping the proposal for a major grant application to USGS. Our final proposal was submitted on Mar 8, 2012.

While we are working on the already existing Population, Climate, and Water modules of our future Human-Earth-System model, we are planning to at least get started with the Food/Agriculture and Energy modules in the upcoming year. This NASA grant is an essential support for this pioneering work. In addition to the support from NASA and submitted proposals, we involve student interns (e.g., Gustafson and Haer) and external collaborators (e.g. Rivas) in this project. Although they are not supported by this grant, they make significant contributions to this pioneering interdisciplinary project. We will offer all of our models and results for potential integration into the Climate@Home project.

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