Content
Introduction and Overview
Today we are going to zoom back out from our very micro-analysis of things like externalities and start thinking about the broader scale again, examining the whole economy. This lecture represents a transition from the detailed examination of market failures and externalities to a more comprehensive view of how economists conceptualize the relationship between economic activity and the environment.
Course Logistics and Schedule
Before diving into the substantive content, it is important to review where we are in the course progression. The current date marks the due date for Assignment 2, and Quiz 2 will be administered during this class session. The quiz will focus on content similar to what appeared in Assignment 2, particularly dealing with marginal abatement cost curves and total cost curves, which are challenging concepts that will be discussed in more detail in subsequent lectures.
Looking ahead, the next class session will feature the first of three guest speakers, Dr. Famara Adamfa, who will discuss sustainability and related topics, including the Kuznets Curve. Students should read through Chapter 11 in preparation for that discussion. Weekly questions number 4 are also due on that day.
The course will then proceed to examine other measures of what we care about as a society. Once we introduce the question of what sustainable development means, the question of what we are really trying to get from our economy becomes central. Questions about whether we should optimize for happiness, GDP, or other metrics will become important topics of discussion.
The midterm exam is scheduled for March 6th, right before spring break. The exam will be the same length as a class period and will be administered in class. It is expected to be approximately twice as long as one of the quizzes in terms of content, with somewhat more variety in question types including some multiple choice questions, but largely similar in format to what students have already seen.
The History of Linking Environment and Economy
The relationship between nature and the economy has deep intellectual roots, extending back at least to Thomas Malthus, and possibly earlier. Understanding this intellectual history is essential for comprehending modern debates about sustainability and the limits of economic growth.
Malthusianism and Population Dynamics
Malthusianism represents one of the foundational arguments that has shaped environmental discourse and often underlies environmental doom and gloom perspectives. The core argument is deceptively simple: population grows exponentially while food production grows only linearly.
Thomas Malthus originally described this as geometric versus algebraic growth, though a more accessible framing is simply that population growth is exponential while growth of the food supply is linear. When we chart this relationship over time, a significant problem emerges.
Population growth is exponential because a larger population means there are more people around to reproduce, which means that the next time period could have an even greater increase. The curve representing population therefore steepens at an increasing rate over time.
The argument holds that because there are fundamental limits on the production of food, food supply will not scale exponentially. There are various discussions about what these limits might be, but a fundamental constraint is that the amount of farmland is relatively fixed. This constraint only relaxes in frontier situations, such as the American frontier, where abundant natural land can be converted to agriculture. In cases where the amount of land is fixed, food production cannot grow exponentially unless one assumes some other factor like technological growth.
Thomas Malthus argued that this dynamic would lead to societal collapse through starvation and other calamities. The key insight from this perspective is the concept of the Malthusian Trap. Whenever more food was produced, it might seem beneficial and perhaps made people happier in the short run, but eventually it simply led to a larger population that would reach a new equilibrium with whatever food could be produced.
It is worth noting that if one examines ecological systems, such as white-tailed deer in northern Minnesota or other wildlife populations, this dynamic is essentially what occurs. These populations exist in a Malthusian trap where the number of animals is essentially a function of the amount of food available to them. While there will be fluctuations, the population continually pushes against its food-based limits.
The Limits to Growth Report
The Malthusian framework set the stage for a second major landmark in environmental-economic thinking: the Limits to Growth report. This famous and, depending on one’s perspective, infamous report studied exponential economic growth with a finite supply of resources. It retained a distinctly Malthusian character but shifted the focus from population to economic growth and expanded beyond just food to consider a finite supply of resources more generally, though food remained one of the factors considered.
This report represents one of the very first instances where researchers used computer simulation of interactions between humans and the environment to draw conclusions about sustainability. While the computers available at that time were far slower than modern technology, the methodological approach of using computational models to understand human-environment interactions remains influential.
The Limits to Growth model built on the Malthusian idea but added considerably more specificity and complexity. Like the Malthusian framework, time is the key dimension, but the researchers attempted to make specific predictions looking both historically and into the future. The model retained many features of the Malthusian framework, including a growing population, but went further in attempting to model what would actually happen rather than simply identifying a problematic inflection point.
The model contained equations defining population growth. As more people inhabit the planet, and particularly as industrial output per capita grows, the problem of collapse emerges. Resources fall toward zero as they are consumed. Industrial production is also a key factor in the model. The total impact on Earth in terms of resource extraction depends on both population and industrialization levels. If people are not consuming very much, they will not have a large impact on the resource stock. However, if consumption patterns include resource-intensive activities like private jet travel for weekend trips, resource use increases dramatically. Therefore, the number of people multiplied by their industrial production levels determines how quickly resources are depleted. As resources become scarce, population collapse follows.
This report was widely influential and appeared simultaneously with another famous work, The Population Bomb by Paul Ehrlich, along with other modern takes on Malthusianism that emphasized doom and gloom perspectives. The common framing was that humanity exists on a spaceship Earth and is running out of resources.
This mode of thinking was widely influential and contributed significantly to the initial environmental movement, which can be considered a positive outcome. However, it was also heavily criticized for fearmongering.
As a side note on the accuracy of these projections, they turned out to be not entirely wrong on many dimensions, though they would be more accurate if shifted somewhat in time. While we obviously have not experienced a population collapse, much of the rest of the predicted impacts, in terms of environmental harm, have tracked more or less on target. The possibility of future population collapse cannot be definitively ruled out.
The Market Versus Environment Perspective
The limits to growth arguments and Malthusian-flavored thinking led to a conception that has dominated much of the discourse: the idea that it is the market versus the environment. This framing positions capitalism and the market as fundamentally opposed to environmental protection.
This is a fascinating question with no definitively correct answer; time will reveal the truth. There are interesting subsidiary questions as well, such as what approaches are most effective for persuading people to change their behavior. The perceived conflict between market activity and environmental protection has waxed and waned over time, but for a long period, environmental considerations and economic activity were viewed as exclusively opposed.
Some factors that pushed thinking in the other direction included increasing emphasis on international equity. This became salient because when low-income countries that had not yet industrialized faced pressure from rich countries to protect their environment rather than grow their economies, many perceived this as fundamentally unfair. Complex questions of justice and development emerge from this tension.
The Great Acceleration
Whatever models we construct could have questions about various elements, particularly regarding whether and how economic and ecological collapse might occur. However, there are essentially no questions about the phenomenon referred to as the Great Acceleration.
This phenomenon has been written about extensively and can be categorized into two buckets of observational data. The first bucket concerns exponential growth in socioeconomic indicators. The second concerns exponential growth in measures of Earth systems trends, or damages to the Earth.
Socioeconomic Trends
On the socioeconomic side, population and GDP both show a clear pattern. Around 1950, many of these indicators reach an inflection point where growth becomes exponential, exhibiting a much faster growth rate. From approximately that point forward, the GDP growth rate has been essentially 3.5 percent per year.
To put this in perspective, consider what the GDP growth rate was between the year 0 BCE and 1500 CE. The answer is approximately 0.01 percent. The economy essentially did not grow; any changes were swamped by regional variation. The current state of exponential growth is actually the exception to the historical rule, not the norm.
The questions of why this acceleration occurred are complex, but it is unavoidably true that there has been an exponential increase in consumption-related activities. Fertilizer use, transportation, and telecommunications have all grown exponentially, with telecommunications growth being even more dramatic. This trend toward acceleration appears to continue into the future. Current spending on artificial intelligence is astronomical, and the growth rate of AI investment has been faster than the adoption of any other technology ever, as measured by dollars. There appears to be a continuing acceleration of economic activity.
Earth Systems Trends
The reason environmental economics matters is that the acceleration of economic activity parallels trends of increasing environmental harm. Carbon dioxide emissions are an obvious example, but one can also examine ocean acidification, fish catch limits, and numerous other indicators.
Integrating Micro and Macro Perspectives
Our goal, which will be developed more fully in the next lecture, is to recognize that the course has so far focused on micro-level considerations: decision-making by consumers and producers, and thinking about optimal pollution levels. However, we will want to take those analytical tools and quantitatively integrate them into the bigger question of how society can remain in what might be termed a safe and just corridor.
This corridor is defined as a space where we are neither overshooting our physical limits nor undershooting or under-providing the key goods and services that we want. The formal arguments that economists traditionally use about economic growth, and what those arguments imply for sustainability, will be the focus of upcoming lectures.
Understanding the Whole Economy: Circular Flow, Growth Models, and GDP
Review: Malthusian Crisis and the Great Acceleration
The previous lecture covered Thomas Malthus and the Malthusian crisis, which describes the scenario where population growth outstrips food production growth. This concept has slightly more modern alternatives, such as the Limits to Growth framework.
The class left off discussing the great acceleration. The goal moving forward is to integrate both sides of the planetary donut, understanding how the exponential growth of the economy has potential downsides to the environment, while also recognizing that economic growth is fundamentally necessary to produce the key goods and services that society needs.
Building a Detailed Model of the Planetary Donut
This section begins adding more detail towards the claim made in the first lecture: that the course will work towards making a more detailed model of the planetary donut. This approach is useful because it incorporates macro goals, like staying within the donut, while maintaining micro-consistency. This means the model ties back directly to the micro theory covered earlier in the course.
The Earth-Economy System
Two Interconnected Systems
There are two different systems to consider: the Earth and the economy. The economy is definitely embedded within the biosphere, but it can be useful to think about these as separate systems because, at least traditionally, they have been studied using very different methodologies.
The relationship between these systems involves impacts, where economic activity affects the Earth, and dependencies, where economic activity relies on environmental services, such as oxygen provision.
Impact Pathways
There are numerous examples of impact pathways from the economy to the environment. Key examples include deforestation, pollution, and water pollution. These represent the traditional environmentalist perspective on the relationship between the economy and the environment, viewing it primarily as one of harm caused by economic activity.
Dependencies
Increasingly, especially when taking an Earth economy framing at a macro level focused on sustainability, there is recognition of dependencies. These include a stable climate, clean water, productive agriculture, and intact biodiverse ecosystems.
Connecting to the Planetary Donut
This framing is useful because each of these two systems corresponds to one part of the donut. Earth systems define the ecological ceiling, while economic systems define the social foundations.
This understanding leads to two different domains that require learning about modeling approaches. For Earth systems, there will be a substantial section on ecosystem services, which attempts to assign specific valuations to how changes in the Earth affect the ecological ceiling.
The course has already established tools specific to the economy. Economic activity, the flow of goods and services, literally creates goods like food, which is obviously important for food security. The simultaneous functioning of both systems is the goal.
The Problem with Conceptual Models
One significant pet peeve in the sustainability space concerns people who develop what they call models, but are really just conceptual ideas. The planetary donut somewhat falls into this category because it discusses indicators without an underlying model that describes the system. The planetary donut is valuable because it provides very detailed indicators, but there is no model that can be used to test how different policies would affect outcomes.
Economics, in contrast, actually has very detailed models. What follows demonstrates how principles of economics can build up to become the calculation engine, the model that allows testing how well society is producing fundamental goods and services.
The Circular Flow Diagram
Basic Structure
The circular flow diagram consists of households and firms as the two types of agents. They are linked by the products market and the factors market. As taught in introductory economics courses, there are two flows of things moving in opposite directions.
Physical Flow and Monetary Flow
The first is the physical flow, which appears on the outside of the diagram. When a firm brings something to the products market, those are goods and services. When a household goes to a store like Target, the products market, and obtains those items, those are also called goods and services.
In addition to this physical flow of things, like a blender moving from the factory to Target to a household, there is an opposite direction flow of expenditures. When a household spends money at the products market, this is called expenditure. When the firm receives this money, it is called revenue.
The Factors Market
The top part of the circular flow diagram represents one half of the story. The conception also explains how firms were able to produce in the first place. The other half, the bottom side, is the factors market.
The household is assumed in this model to initially own the endowment of capital and labor. Labor is fairly obvious; everyone possesses their own labor. It is somewhat more arbitrary to say households own capital, but nonetheless, they sell these factors to firms in the factors market.
The firm has an opposite direction flow, paying things like wages, rents, interest, or profit. When experienced by the household, this is called income.
Beyond Principles of Economics
This is typically where a Principles of Economics class stops, so this material is familiar. However, at intermediate or more advanced levels, these elements become ever more detailed and fit together in a beautiful symphony of connections.
The circular flow diagram is not merely a conceptual model. It is not something that fails to specify how variables and functions relate; it is a specific model. The dynamic version on the course website demonstrates this.
The Micro-Founded Circular Flow Diagram
Household Optimization
The household maximizes utility subject to a budget constraint. This can be visualized graphically with an indifference curve and a budget constraint. This determines exactly how much of a product a particular household will want to use.
Making this dynamic and computed directly shows what happens when, for instance, income increases. The indifference curve and budget constraint shift. With more income, households can simply afford more things. This produces more overall utility, but it also changes supply and demand. As income changes, demand increases and shifts right. This is one of the shifters taught in principles courses.
Supply and Demand Equilibrium
This leads to a supply and demand graph derived from the household’s optimization. The equilibrium is predictive in that this price is what will happen; otherwise there are surpluses or shortages of goods being produced. This information feeds down to the next part of the model.
Firm’s Problem
A simple representation of the firm’s problem shows they maximize profit subject to production costs. At a given price, a particular firm may be doing very well. The firm might make substantial economic profit because they set their production level where marginal revenue, which equals price in a perfectly competitive firm, equals marginal cost.
Production Function and Factor Markets
The story continues: production is valued by the consumer, but there is also a consistent way of explaining how production happened. What goes into the production function is equivalent to asking what are the costs. These are the things the firm needs to buy, in this case from households: another supply and demand relationship, but for labor.
All different combinations can be explored. The factors of the household can be adjusted. The overall productivity of the firm can be modified, and as they produce more, GDP goes up.
GDP as a Metric
This approach allows extraction from the circular flow diagram of a metric of how well the economy is doing. Politicians often discuss how great the economy is doing using GDP as the primary metric. They favor it because it is easy to explain. Despite its downsides, GDP is evident and based on a theoretically consistent approach called being micro-founded. This means it is derived from a very basic idea of consumer and producer behavior.
This is a real simulation that solves the maximization of utility and profits simultaneously. Different scenarios can be explored, such as what happens if many firms enter the market. The supply curve shifts. This is good for GDP, but not good for individual suppliers because there are more of them now, dividing the pie into smaller and smaller portions.
The Value of Micro-Founded Models
This tool provides a really well-defined metric of the social foundation. Of course, it is oversimplified, with GDP missing some details, but it does capture other details that matter, like different sectoral outputs. A more complicated version of this graph could include healthcare as a sector, or food as a sector, providing real computational estimates of those things.
In many microeconomics classes, the microeconomic theory of profit maximization and utility maximization is not tied to the circular flow diagram. About half of classes actually attempt to get to that point. This connection is important because it demonstrates that very micro-defined elements add up to something macroeconomic in nature. It is very consistent.
The Economy-Earth Tension
The Problem of Scale
The problem is that the economy itself has now grown so large that the impacts of the economy on the Earth are undermining the stable flow of dependencies from the Earth.
This represents a novel way of expressing the problem. This perspective is not found in a standard environmental natural resources class. It might appear in a sustainability class, but it represents relatively new research, an emerging synthesis of how to tie these two things together.
A conceptual graphic illustrates this: when the economy is small, it fits within the ecological ceiling. But as more goods and services are produced, as society moves out of the Depression into a world of affluence with abundant goods, the economy gets bigger. The problems of the social foundation, producing enough goods, are no longer the main issue. Instead, the concern is systematic overshoot of the ceiling.
Understanding Economic Growth
Growth as a Key Variable
The key variable in much of this discussion is growth. On one hand, this relates to how much old environmentalism was focused on being anti-growth, anti-GDP. Movements such as degrowth or steady-state economics reflect considerable interest in the idea that stopping growth would solve the problem.
Throughout this course, the argument will be that the situation is more complex. Both the ecological ceiling and the benefits of production must be considered. The analysis will be more detailed than the standard environmental criticism of economics.
To understand this complexity requires diving deeper into how economists actually think about growth, because growth is one of the key variables underlying all of this. What follows builds out the mathematics of how economists like to think about growth.
The Ramsey Model
Frank Ramsey’s Contributions
Frank Ramsey is probably unfamiliar to most people. He was an absolute genius who made fundamental advances in three different fields: philosophy, mathematics and logic, and economics. All of this came before the age of 26, because he died tragically young. He created the mathematics that became the standard economic way of thinking about why economies grow.
Why Economies Grow
If asked for the most simplified definition of why economies grow, an economist might say something like: capital accumulates. Capital refers to things like factories and inputs to production. The interesting property of capital is that capital existing in one time period will probably still exist in the next time period. If the amount of capital keeps growing through more factories and more tools, this provides the underlying source of economic growth.
The Optimal Amount of Growth
Frank Ramsey addressed the question of how to determine the optimal amount of growth, and how consumers maximizing their own utility would choose, hopefully, the ideal amount of growth to have.
This becomes a maximization problem, maximizing a utility function. The main difference from previous models is simplification: utility depends just on one thing, C for consumption, but subscripted with T because economic growth obviously happens over time, requiring more than just a single time period.
The setup is similar to before but simplified. It is a maximization, but instead of being subject to a budget, Ramsey decided to incorporate production into the same agent. The person maximizing utility is also going to choose production.
The constraint states that the amount of consumption in the utility function equals the production function. This mixes from both sides of the circular flow diagram. There is utility, but the constraint is a production function that depends simply on how much capital is used.
The Investment Decision
One more element is added: consumption equals production minus investment. The thinking is, if production yields 100 units of economic activity, at most 100 could be consumed. But if only 90 is consumed, the remainder of 10 is called investment.
Investment means foregoing consumption, subtracting I from available production. This is useful because capital in the next period, K(T+1), equals capital in the current time period plus investment.
The Basic Growth Story
The basic story emerges that it is undesirable to consume all production right away. It is better to invest, grow the capital stock, and be able to produce more in the future. Foregoing consumption now might be beneficial because it enables more consumption later.
This is the most basic, stripped-down version of economic growth, but it underlies the key models that institutions like the Federal Reserve Bank of Minneapolis use when calculating projections for economic growth. They essentially solve this question but with more detail and ties to the real economy.
The Solow Growth Model
Beyond the Ramsey Model
The Ramsey model is a useful concept, but it is so simplified, with one consumption good and one agent producing that consumption good, that it is difficult to tell a rich story about the economy. More detail is needed.
The Production Function
In particular, the production function will take the form: output equals capital raised to some exponent alpha, multiplied by labor. This states that output, and because this concerns the whole economy, that means production or GDP, is created by mixing together some version of labor and capital.
This is more realistic in the sense that machines in a factory are a significant part of the production process, but people are still involved doing something. Perhaps not for long, as robots might take over. Robots are basically like human laborers but are not humans, so they count as capital. There is extensive debate on this topic, but basically the ratio of capital to labor is changing and evolving over time, and AI and robotics might be shifting this fundamentally.
Robert Solow’s Contributions
With this relationship established, the second model is the Solow growth model, named after economist Robert Solow. He builds on the basic idea but adds more detail, both on the sectors of capital and labor, and on how the capital stock evolves over time.
The notation defines K as capital and L as labor. Time subscripts are added because the Solow model solves for the optimal levels of K and L at each time period T. This is necessary for understanding economic growth.
Capital Accumulation Over Time
The production function Y(T) evolves over time depending on two different things: investment and depreciation.
The equation states that K(T+1), capital in the next time period, equals capital in time period T multiplied by D, the depreciation rate. Some formulations use 1 minus D. For example, if the depreciation rate is 0.95, that means every year, without any other changes, the capital stock decreases by 5%. This is depreciating capital; literally, things break.
The second component is investment. Investment equals Y(T), total production at time T, minus C(T). Whatever is not consumed goes in as capital to be used in the next period.
The Condition for Growth
With this setup, economic growth happens if the capital invested accumulates the total capital stock faster than it depreciates. This should hopefully be the case. It would be irrational to invest in the economy if depreciation was so severe that production could not actually compensate for it.
What would create such a situation? A war. Bombing represents depreciation. This is why economic growth goes negative during wars. Even if production of tanks increases, depreciation of the capital stock through literally bombing factories causes negative growth.
The basic story is that capital accumulation leads to growth. The Solow growth model, which won the Nobel Prize, has become a workhorse model for explaining how key variables within an economy fit together to produce GDP.
Integrating Growth Models with the Circular Flow Diagram
Consistency Across Frameworks
The growth models might seem quite different from the circular flow diagram. There are some similarities: there is a utility component and a production function. But remarkably, everything still fits together into the circular flow diagram.
The circular flow diagram can actually be observed in operation. The course website has two versions demonstrating this.
The Financial Market
The simplified version shows the exact notation that has been defined, placed on the appropriate parts of the circular flow diagram. The key addition is the financial market. This enables the transition of wealth from one time period to the next.
This is where the K(T+1) function appears, showing exactly what was defined: depreciated capital plus investment. This illustrates that investment comes from savings. A household maximizes utility, but one consideration is future utility, so it might become optimal not to consume everything but to invest some in economic growth.
This flows into the financial market. The equation is straightforward: savings becomes investment. They are tracked as different variables because they feel different. One represents a household giving up consumption, another represents a firm receiving resources. But savings becomes investment, expressed as a growing capital stock.
There is also a dotted line for depreciation, representing the net flow of capital. This is how the concepts fit conceptually.
The Dynamic Simulation
A more elaborate version simulates the model. It solves the equations over time using mathematical methods or direct computation for the larger Solow growth model.
The simulation can be stepped from one time period to the next. Running it shows 212 years of economic future being simulated. With each step, different indicators change: Y for total production, the capital stock, consumption, and GDP.
Depending on the parameter set, clicking step forward shows GDP growing. Eventually, it reaches an equilibrium. This relates to a separate finding that bigger economies grow slower.
This is not surprising. Part of the explanation is that larger economies have already utilized all technology advances, while lower-income countries still have catch-up potential because they can implement existing technologies. Eventually, the economy converges to a steady state.
The visualization shows boxes growing bigger and arrows growing thicker, representing GDP increases. The size of arrows directly represents the value of flows. At later stages, investments just barely stay ahead of depreciation, which is why the economy grows slower. Resetting and running from the beginning shows growth being much more effective, with substantial investment and relatively low depreciation.
Exploring Parameters
Different parameters can be explored, such as people’s preference for savings. If people strongly prefer saving, what happens? In a society where people value future utility highly and save a lot, what occurs?
The money not spent on consumption becomes investment, which turns into capital stock. This is somewhat counter to how the economy is normally discussed. News reports emphasize consumer confidence. When consumer confidence goes down and people buy less, being cautious with their money, this results in less growth if money just stays in bank accounts.
However, the model simplifies this. The savings equals investment assumption means instead of growing a stockpile in a bank or under a mattress, all money not spent goes towards capital accumulation.
Playing with this parameter shows that as people want to consume more, the equilibrium amount of investment goes down. Considering the opposite question: how effectively would an economy grow if a person consumed every single bit of product produced?
Without any investment, the capital stock would break down. Factories would not be maintained. This would be equivalent to a farmer eating all produce and keeping none as seed. There is an optimal amount of seed to keep. Having only seed is not useful because it cannot be eaten. But consuming all corn with no seed corn remaining leads to being much worse off.
There is an intertemporal trade-off between consuming everything now, which provides immediate satisfaction, versus maintaining the ability to grow the capital stock.
The Beauty of Theoretical Consistency
This demonstrates how all these components fit together. No part of this is unanswered. It provides a theoretically consistent approach that is not just derived from first principles but is also quite predictive.
This is why Federal Reserve Banks run models like this. They can observe economic indicators like hiring, wage rates, and consumer purchases in time period T, and make predictions about what consumption will be in T+1.
This capability is extremely important because central banks have important policy tools, like interest rates, or decisions about investing in certain types of goods for use in the next period. If they can make good estimates of how much GDP will be produced in the next time period from current data, they can better manage the economy.
Referring back to the first or second class session, the frequency of recessions was shown. There was approximately a three-fold reduction in recession frequency at about the same time that central banks started using tools like this. This represents a positive development.
Applying Models to Earth Economy Questions
From Prediction to Policy Analysis
Having this model allows asking questions of it, like what would happen if people consumed more and saved less. Counterfactuals, what-if scenarios, become possible.
Beyond just predicting economic activity, these tools can be tied back into the broader framework. The focus turns to thinking about how economists have made significant progress on problems of underconsumption. This is premised on the idea that during the Great Depression, there truly was a case of underconsumption, and tools like those discussed helped navigate out of that situation.
The Shift to Overconsumption
But as the economy has grown and started to push planetary boundaries, challenges have morphed more into ones of overconsumption. To understand the optimal trade-off between economic activity and the downsides of economic growth, a detailed representation of both is needed.
The circular flow diagram with a savings and growth mechanism built in is the basic idea for making progress. This is where the course is heading. There will be a return to these concepts, actual computations, and policy experiments. This work will be conducted with different countries that will ultimately form the basis of final projects.
A Physical Model of the Economy
The Monetary Income Analog Computer
The goal is building a model, which is a mathematical construct. But a model can also be thought of as literally a physical model. A group created the Monetary Income Analog Computer (MONIAC).
This device shows how water flows through the economy. There is an income source at the bottom. Water flows to households. Some is taxed. Taxes go to the government, and the government fund continues the flow.
This provides an example of where the course is heading: creating a model. The water-based model might be useful because it could make predictions about how changing the interest rate would affect the economy. It is a pretty inefficient way of computing because it uses water pumps instead of mathematical functions.
But the idea is the same: there are inputs and outputs, which were calibrated. Surprisingly, the creators were actually able to calibrate the model, basically changing the relative strengths of pumps, until the thing was surprisingly accurate.
Essentially, they ran the model on historical time series of economic data and used it to see if it could predict what would happen in the next period. They achieved accuracy within 2%, which is remarkable.
The Limitations of GDP
A Narrow Metric
GDP is a narrow metric. It is simplistic and elegant, and it is at least in some way related to well-being because people enjoy consuming food, for instance. But GDP leaves out a tremendous amount.
Looking Ahead
This is where the guest lecturer on Monday will pick up the discussion. He will talk about sustainable development, which essentially involves growing the economy and increasing the capital stock. Sustainable development applies this to real countries while trying to define it in a way that accounts for the environment. He will also discuss GDP and its flaws, as well as potential replacements for GDP.
Conclusion
This lecture has covered the theoretical foundations linking microeconomic behavior to macroeconomic outcomes through the circular flow diagram, introduced the Ramsey and Solow growth models as frameworks for understanding capital accumulation and economic growth, and positioned these tools within the broader Earth economy framework that will guide the remainder of the course. The key takeaway is that rigorous, micro-founded economic models provide both predictive power and a platform for policy analysis, but they must be integrated with environmental considerations to address contemporary challenges of sustainability.