Student Materials for Modeling Earth Systems

Welcome students!

Computer modeling has become very important in Earth and environmental science research as a means to generate and test hypotheses and to allow simulation of processes in places inaccessible to humans, too slow to permit observation, or too large to facilitate construction of physical models. Entire fields in Earth and environmental sciences now exist in which computer modeling has become the core work of the discipline. These include simulations of past climates, seismic hazard research, hydrogeology, and ecological modeling. In this course, you will learn the basics of numerical modeling in the context of the global climate system. We will explore topics such as what determines Earth's surface temperature, how variations in solar radiation affect the growth and decay of ice sheets, how climatically controlled changes in salinity impact ocean circulation, and how the carbon cycle works. We will also carry out exercises to investigate the role of life in moderating Earth's climate, paying particular attention to human greenhouse gas production. Below, you will find brief descriptions of each week's activity along with an accompanying reading.

Unit 1: Introduction to Modeling Dynamic Systems

In this unit, we introduce the fundamentals of systems thinking and the STELLA software that we will use all semester to construct and experiment with numerical models. We will use examples of bathroom sinks, bank accounts, and a cooling cup of coffee to learn about reservoirs and flows and how they are interrelated.

Unit 1 Reading: What are models, why do we use them, and how do we build them?

Unit 2: Modeling Population

This week's activities explore the factors that govern the growth of populations of organisms. We will start with a predator-prey model that exhibits interesting cyclic behavior, move on to see how populations can stabilize as they reach a particular carrying capacity, and end with a model of the growth and collapse of the human population on Easter Island in the South Pacific.

Unit 2 Reading: Growth and Dynamics of Populations

Unit 3: Simple Climate Models

Earth's temperature reflects a balance between incoming energy given off by the sun and outgoing energy reflected and radiated to space by our planet's surface. In this unit, we model this "radiative equilibrium," beginning with a very simple model of an Earth with no atmosphere and no reflectivity, and ending with an Earth whose surface both reflects and absorbs solar energy and that has an atmosphere. We further explore the impact of changing greenhouse gas levels, volcanic eruptions, sun spots, and human-produced aerosols on our planet's temperature.

Unit 3 Reading: Earth's Energy Balance

Unit 4: Daisyworld

In this week's exercise, we build on the population modeling and simple climate model exercises of the two previous weeks to study how life can moderate the temperature of a planet exposed to the energy being given off by a star (like our sun) that is getting hotter over time.

Unit 4 Reading: Daisyworld

Unit 5: Growth and Decay of Icesheets

This week's activities explore how changes in climate can trigger ice sheet expansion or catastrophic collapse. We will build a model that incorporates the basic physics of ice flow and then subject our simulated ice sheet to changes in solar radiation inputs driven by the Milankovitch orbital cycles.

Unit 5 Reading: Ice Sheet Modeling

Unit 6: Hydrologic Balance and Climate Change

Closed basin lakes (lakes with no outflow streams) have often been called "nature's rain gauges" because they grow and shrink in response to climate change. In this week's project, we develop a model of the Owens River chain of lakes in eastern California and explore what happens as we vary precipitation and evaporation rates.

Unit 6 Reading: Great Basin Lakes - Nature's Rain Gauges

Unit 7: Heat Flow in Permafrost

In the 1980s, clever geophysicists discovered that permafrost—perennially frozen ground in the Arctic region—records evidence of global warming. We will create a model of heat flow through a 1-km thick layer of permafrost and see how climatic changes at Earth's surface affect the profile of temperature with depth.

Unit 7 Reading: Global Warming Recorded by Permafrost

Unit 8: Thermohaline Circulation

In this unit, we examine the impact of changing sea surface temperatures and salinities on the thermohaline circulation of the oceans.

Unit 8 Reading: Modeling Thermohaline Circulation

Unit 9: Carbon Cycle and Ocean Chemistry

Human combustion of fossil fuels and deforestation for the purpose of agriculture and settlement have led to dramatic increases in the amount of carbon dioxide in Earth's atmosphere. In this exercise, we model the impact of rising greenhouse gas levels on ocean chemistry and assess the relative economic benefits of different greenhouse gas reduction scenarios.

Unit 9 Reading: The Global Carbon Cycle

Unit 10: Coupled Economic and Environmental Models

Many environmental problems also carry economic costs. In this unit, we create a model of ecologist Garrett Hardin's Tragedy of the Commons problem, a parable of how resources can be degraded without appropriate regulations.

Unit 10 Reading: The Tragedy of the Commons