Re-Examining the Future of Power Generation
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Letters to the Editor Re-Examining the Future of Power Generation To the Editor: Please allow me to make a comment on the article by B.L. Eyre and J.R. Matthews on “Materials for the Power Industry,” published in the July 2001 issue of MRS Bulletin [p. 547; www.mrs.org/publications/bulletin/21stcen/]. The authors deal with the very important issue of energy supply and sustainable growth for humankind in the 21st century. I got the impression that their article was somehow missing the strategic top-to-bottom approach which is necessary for such an issue. The authors think furthermore that developing countries need (at least initially) cheap solutions, rather than sophisticated ones. In a world of global communication, where everybody knows the state of the art, and in times where we realize that we are all sitting in the same “Spaceship Earth,” this sounds like political discrimination. Developing countries, in my opinion, need state-of-the-art technical solutions as rapidly as possible, in order to prevent unnecessary pollution and tearing-up of the planet’s resources. The authors tie global warming in a simplistic way to CO2 production. The physical factors influencing the earth’s surface temperature are, however, manifold, and CO2 concentration is only a minor contributor among them. To properly assess the problem of global warming, if ever there is one, we need a quantitative balance of the energy flows to and from the earth’s surface. The earth receives about 95% of its relevant energy input from the sun, at a rate of ~1 kW/m2 on vertical solar incidence. This energy has a short-wave blackbody-radiation spectrum, peaking at 500-nm wavelength (corresponding to a radiator temperature of about 6000 K). If the surface temperature of the earth is to remain at steady state, the total of the received and produced energy on earth must be radiated out to space. Part of the received solar energy is directly reflected back to space by the earth’s surface “whiteness” (albedo) or by the clouds. This direct reflection occurs almost unhindered because the earth atmosphere is not absorbing significant parts of the 6000 K blackbody radiation. The remaining part of the solar energy is absorbed and converted to long-wave infrared radiation, peaking at 10-µm wavelength (corresponding to a radiator temperature of about 300 K). The escape of the 300 K radiation from the earth’s surface is partially impeded by absorbing components in the earth atmosphere (greenhouse gases, greenhouse effect).
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CO2 has two relatively narrow spectral absorption bands in the thermal infrared, at 4.3-µm and at 13.9-µm wavelength, respectively. Between these bands, there is a large atmospheric window extending from ~7-µm to ~12-µm wavelength, through which the 300 K IR radiation of the earth’s surface normally escapes into the 3 K cold space. The CO2 concentration in the atmosphere is such that both spectral bands are already largely saturated under natural conditions, and the humanmade increase in CO2 concentration does only show up as a second-orde
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