When we think about climate change, we think big. Big problem, big impasse, big data. What could be more complex than the climate of the entire world and how it changes chaotically?
And, as usual, when faced with too many dimensions of information to compute, we simplify. We focus on the amount of carbon burned, or the rise of surface temperatures, catastrophic storms or sea levels. Or, conversely, we deny that any of these things are other than “natural change.”
What is often missing in the debates about climate change is a fundamental understanding of the system that is doing the changing. How we define this system and what we see flowing within it is key to making decisions about how to respond.
Duke Professor, Adrian Bejan, spends his days defining flow systems of all kinds. In his book, Design in Nature, he describes the Constructal Law that shows how flow systems create configurations that increase in efficiency over time. Climate, to Bejan, is just another such system.
Along with collaborators Marc Clausse, Francis Meunier and Antonio Heitor Reis, Bejan set out to create “a simple and transparent alternative to the complex models of earth’s thermal behavior.” Their model shows the balance of convection and radiation—how the earth is heated by incoming energy from the sun and how some portion of that energy is radiated back out into cold space. The variables that change over time are the reflectivity of the earth, or albedo, and the concentration of greenhouse gases in the atmosphere. Greenhouse effects cause terrestrial temperatures to rise and increased reflectivity cause them to go down.
Human energy consumption, widely seen to be the irrefutable cause of climate change, increases the concentration of carbon and other greenhouse gases in the environment, but it also increases the amount of aerosol particles that make the earth more reflective. So the push and pull between these two forces creates what is called a “net forcing” effect on the climate.
Using the mathematical equations of this model, it is possible to show that as the overall “net forcing” increases, the heat will flow in certain predictable pattens—more near the poles and less closer to the equator, that correspond with actual recorded observations. Bejan claims that the math is “simple enough to be calculated with pencil and paper using readily available data.” I don’t know how sharp your pencil is, but the equations in their paper, Climate Change in the Framework of the Constructal Law, are beyond me.
Because I couldn’t do the math myself, I had to rely on my verbal skills to extract out of Bejan, over a series of exchanges, what is interesting and significant about this model. In a news release from Duke, Bejan says, “Complex models of the Earth’s thermal behavior are opaque from the point of view of the average person, and contain the uncertainties of the many flows of various scales that are part of these models. Our approach is much simpler.”
Bejan contends that existing computer models of climate change are opaque—and controversial—because they muddle together three ideas that should be seen as distinct entities:
The first is our projections of energy use and carbon emissions in the future. It is fairly non-controversial that human energy use is growing faster than human population. In another recent paper, Bejan shows that growth in global energy consumption follows an S-curve pattern with no flattening of the curve in sight. The paper also shows that the rise in energy consumption is roughly linear with the rise in global GDP. Social justice demands that we do not frame the issue in a way that denies the developing world the prosperity that the developed world enjoys, so the only real question is how much of this increased energy usage will take the form of renewables that do not add to the climate equations. This corresponds to the greenhouse effects variable in the new model.
The second is how this growth in energy use affects the composition and radiative properties of the atmosphere. This corresponds to the albedo variable in the model. Unlike carbon emissions, which are growing in a fairly predictable (and consistant) rate, “Earth’s albedo is strongly controlled by clouds,” points out Bejan’s collaborator Reis, and “Large uncertainties exist about the combined effect of aerosols (namely carbon aerosols) and greenhouse gases.” Reis cites a report (Stevens and Feingold, 2010) that summarizes the current aerosol-cloud-climate conundrum: “Despite decades of research, it has proved frustratingly difficult to establish climatically meaningful relationships among the aerosol, clouds and precipitation. As a result, the climatic effect of the aerosol remains controversial. We propose that the difficulty in untangling relationships among the aerosol, clouds and precipitation reflects the inadequacy of existing tools and methodologies and a failure to account for processes that buffer cloud and precipitation responses to aerosol perturbations”
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