To: Taro who wrote (851824 ) 4/23/2015 6:48:23 PM From: Wharf Rat Respond to " believing man can seriously influence the behaviour of our mother Earth is nothing but Hubris"Like many Victorian natural philosophers, John Tyndall was fascinated by a great variety of questions. While he was preparing an important treatise on "Heat as a Mode of Motion" he took time to consider geology. Tyndall had hands-on knowledge of the subject, for he was an ardent Alpinist (in 1861 he made the first ascent of the Weisshorn). Familiar with glaciers, he had been convinced by the evidence — hotly debated among scientists of his day — that tens of thousands of years ago, colossal layers of ice had covered all of northern Europe. How could climate possibly change so radically? - LINKS - <= Climate cycles One possible answer was a change in the composition of the Earth's atmosphere. Beginning with work by Joseph Fourier in the 1820s, scientists had understood that gases in the atmosphere might trap the heat received from the Sun. As Fourier put it, energy in the form of visible light from the Sun easily penetrates the atmosphere to reach the surface and heat it up, but heat cannot so easily escape back into space. For the air absorbs invisible heat rays (“infrared radiation”) rising from the surface. The warmed air radiates some of the energy back down to the surface, helping it stay warm. This was the effect that would later be called, by an inaccurate analogy, the "greenhouse effect." The equations and data available to 19th-century scientists were far too poor to allow an accurate calculation. Yet the physics was straightforward enough to show that a bare, airless rock at the Earth's distance from the Sun should be far colder than the Earth actually is. <= Simple models Tyndall set out to find whether there was in fact any gas in the atmosphere that could trap heat rays. In 1859, his careful laboratory work identified several gases that did just that. The most important was simple water vapor (H2O). Also effective was carbon dioxide (CO2), although in the atmosphere the gas is only a few parts in ten thousand. Just as a sheet of paper will block more light than an entire pool of clear water, so the trace of CO2 altered the balance of heat radiation through the entire atmosphere. (For a more complete explanation of how the "greenhouse effect" works, follow the link at right to the essay on Simple Models of Climate. ) (1) aip.org
