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. 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 rock at the Earth's distance from the Sun should be far colder than the Earth actually is. Tyndall set out to find whether there was in fact any gas 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 (H[SIZE=-1]2[/SIZE]O). Also effective was carbon dioxide (CO[SIZE=-1]2[/SIZE]), 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 CO[SIZE=-1]2[/SIZE] altered the balance of heat radiation through the entire atmosphere. (
For full explanation of the science, follow the link at right to the essay on Simple Models of Climate.)
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