Thursday, November 27, 2008

Modelling civilization as 'heat engine' could improve climate predictions

Environmental Research Web has a fascinating article by science journalist Edwin Cartlidge: The extremely complex process of projecting future emissions of carbon dioxide could be simplified dramatically by modelling civilization as a heat engine. That is the conclusion of an atmospheric physicist in the US, who has shown that changes in global population and standard of living correlate to variations in energy efficiency. This discovery halves the number of variables needed to make emissions forecasts and therefore should considerably improve climate predictions, he claims.

Computer models used to predict how the Earth’s climate will change over the next century take as their input projections of future manmade emissions of carbon dioxide. These projections rely on the evolution of four variables: population; standard of living; energy productivity (or efficiency); and the “carbonization” of energy sources.

When multiplied together, these tell us how much carbon dioxide will be produced at a given point in the future for a certain global population. However, the ranges of values for each of the four variables combined leads to an extremely broad spectrum of carbon dioxide-emission scenarios, which is a major source of uncertainty in climate models.

Timothy Garrett of the University of Utah in the US believes that much of this uncertainty can be eliminated by considering humanity as if it were a heat engine (arXiv:0811.1855). Garrett’s model heat engine consists of an entity and its environment, with the two separated by a step in potential energy that enables energy to be transferred between the two. Some fraction of this transferred energy is converted into work, with the rest released beyond the environment in the form of waste heat, as required by the second law of thermodynamics….

A desktop Stirling engine. The working fluid in this engine is en:air. The hot heat exchange happens in the glass cylinder on the right, and the cold heat exchanger is the finned cylinder on the top. This engine uses analcohol burner (bottom right) as a heat source. Photo by Richard Wheeler (Zephyris), Wikimedia Commons, under the terms of the GNU Free Documentation License, Version 1.2

1 comment:

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