I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.
By: Dr. Ricky Rood , 6:17 PM GMT on September 22, 2012
The Free Market and the Climate Model: Models, Water, and Temperature (8)
I am returning to my series of blogs on models, water, and temperature (see Intro, and previous entry). The earlier entries in the series are linked at the end.
The previous blog was a diversion from the series and reported on A National Strategy for Advancing Climate Modeling. Accompanying the publication of that document a new website was published Climate Modeling 101, which is an introduction to modeling more anchored in scientific language than the series I am currently writing. Give it a try.
Doing Science with Models 1.5: I have used the example of balancing a checkbook to write about the balance of energy at the center of the study of the Earth’s climate. I have shown that despite the simplicity of balancing the budget of a single account, there are many ways in which complexity emerges.
Let’s look at just one of these exchanges of energy, say between the atmosphere and ocean. We have wind in the atmosphere, which as it blows over the ocean, exerts a stress that causes waves and large surface currents, for example, the The Gulf Stream. The Gulf Stream is a warm-water current that carries heat from the Gulf of Mexico to the high latitudes of the Northern Hemisphere. At high latitudes, heat is transferred from the warm water of the Gulf Stream to the air. This heat keeps western Europe far warmer than would be the case if warming came only from the Sun. We have here the transfer of energy by motion of air and water, referred to as kinetic energy, as well as the transfer of heat or thermal energy between air and water.
Rain also represents energy transfer. We naturally think of rain as a source of water. However, in order for water to get into the atmosphere from the ocean, it must evaporate – turn from liquid to vapor. This takes energy, just as you have to add energy to a pan of water to boil it. This type of energy is latent energy, because it just sits in the water vapor until it gets cold enough to give up that energy as it condenses back to liquid water or ice, maybe many thousands of miles from where it evaporated.
If you focus on evaporation, then the heat from the Sun that is absorbed at the Earth’s surface is one source of the energy that evaporates water. So in our accounting problem, we account for some energy from the Sun that is absorbed at the ocean’s surface, which evaporates water, transferring energy to the atmosphere that is released in the atmosphere when it rains.
Hence, as we break down the problem to understand the accounting of energy between the ocean and atmosphere, we find several types of transfers that can occur. If we extend our consideration to the land, then we would consider trees, which take up energy from the Sun to drive photosynthesis and move liquid water from the soil to water vapor in the air through their roots and leaves. If we are doing an accounting of what trees do, then we have to take into the specifics of different types of trees: oaks behave differently from pines and bristlecone pines behave differently from loblolly pines. Trees behave differently from grasses, which are different from cacti, which are different from mushrooms.
The diversity of the natural world presents us with enormous complexity when we desire to describe it quantitatively. But at the foundation of the accounting is the budget equation for energy
Today’s Energy = Yesterday’s Energy + Energy Gained – Energy Lost
We write an energy equation for the atmosphere, and that energy equation will include how much energy is lost to the land surface over grassy surfaces, tree covered surfaces, and sandy deserts. There will be contributions to the energy equation for each process on Earth that our point of view brings us to. The total energy accounting is computed by adding up all of these energy transactions.
I want to return, now, explicitly to the budget equation for money. I made the point in Ledgers, Graphics, and Carvings that many of us have become familiar and comfortable with the idea of using computers to do our accounting and account balancing. The budget equations that represent our checking and savings accounts and the transfers between them are managed by software like Quicken or in spreadsheets like Excel. It is possible to do monthly accounting to the penny. If we think about our credit union, it manages thousands of accounts with near-perfect accuracy. A large bank manages millions of accounts, and a credit card company manages billions of transactions. Therefore, it is routine to accumulate millions of accounts and billions of transactions into large calculations. This sort of accounting problem is large and complex and requires diligence, rigor, and checking to get correct. The same is true with climate modeling. Each of the sales and returns and the transfers are, individually, simple, and in their total, complex. All of these financial accounting challenges are shared with climate modelers. The fact that we can do this financial accounting should demystify climate modeling. The complexity is a challenge, but it does not suggest impossibility. There is no magic that has to be invoked in the building of a climate model. (And, yes, you could write a climate model in Excel.)
As we collect information from all of our financial accounts, we start to describe our economy. In the United States, we imagine that we want a free market, one whose behavior is described by the law of supply and demand. If there is low supply and high demand for gasoline, the price is high. If there is high supply and low demand for terrier sweaters, then the price is low. Our purchase of gasoline and terrier sweaters is a loss of money to us, but a gain of money to their respective industries. We also make money itself a marketable item; we loan and lend for a price. We find these relations that emerge, for instance, when money is tight, then it costs more to borrow. Again, it is an issue of supply and demand, which is viewed as a defining law of markets and economies.
It is at this point of my comparison of financial budgets with energy budgets that an important difference emerges. It is in principle easier to predict the Earth’s climate than it is to predict how our economy will evolve. Why? Behavior. In financial transactions and our economy, people make decisions based upon necessity and whim. The fortunate among us might spend vast amounts on terrier sweaters, simply because we want terrier sweaters. The energy transactions in the Earth’s climate are far more boring: they are constrained by physical laws of conservation. The amount of rain cannot be just any number. It can be no more than the amount of water vapor that is available in the atmosphere to condense and fall out. The sea ice in the Arctic requires a certain amount of energy to melt. Once that melting has occurred, additional heat warms the ocean, and some of that heat expands the water. There are strict limits on behavior of the individual parts of the Earth’s climate, which do not hold true when buying and selling.
For the Earth’s climate, a strong constraint in any quantitative description is the amount of energy provided to the Earth by the Sun. The Sun is relatively stable in the amount of energy that it emits. Over the life of the Sun, its energy emission has increased by about 25 percent (Newman and Rood (Robert)). Over the span of a human life, the Sun varies up and down only a percent or so. But this is not true with money. We print money as our economies and populations grow. We try to engineer a stable economy, which actually means an economy that is growing fast enough to provide employment to an increasing population. This requires exploitation of new resources, innovation, fashionable ideas, or, perhaps, printing more money.
There is no denying that quantifying the observed behavior of our climate is a problem of immense complexity. It is, however, not a problem that is difficult to conceive. We have simple relationships based on calculating budgets of energy: production, loss, and transfers. These relationships define and constrain behavior of the processes that make up the climate as a whole. There is no free will, no credit, no overdraft protection to behave outside of these constraints. Arguments that the climate problem is too large and too complex to model and understand are simply spurious. We just require diligence, rigor, and checking our work in our accounting.
Models, Water, and Temperature
Models are Not All Wet: Series Introduction
Models are Everywhere
Ledgers, Graphics, and Carvings
Balancing the Budget
Point of View
Looking Under the Cloak of Complexity
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