Preference was given in the past to immigrants from those countries from which South Africa's present white population is derived. Between 1963 and 1984, the number of immigrants averaged about 37,000 annually, and the number of emigrants about 12,000. Between 1980 – 84, some 72,528 Zimbabwe residents emigrated to South Africa. After 1984, immigration fell, and, perhaps as a consequence, the white population actually declined between 1980 – 91. Of the 63,495 immigrants between 1986 – 91, 16,815 came from other African countries, 16,056 from the United Kingdom , 16,512 from other European countries, and 14,112 from other parts of the world. Emigration came to 46,541 during these years.
The first scientist to propose that increased carbon dioxide could alter the atmosphere was a Swedish chemist named Svante Arrhenius. In the late 1890s, he studied the paper that had been written by Jean-Baptiste-Joseph Fourier about seventy years before. Arrhenius agreed with Fourier about the role of heat-trapping gases in the atmosphere, and he was intrigued with the scientist's theory that the earth acted like a giant glass vessel that trapped and held heat. Arrhenius took the theory one step further, though. He suspected that humans were causing the gases to accumulate at a faster-than-normal rate because of the burning of fossil fuels such as coal. Arrhenius thought it was logical that as more fossil fuels were burned, more carbon was released into the atmosphere. He believed this could cause atmospheric carbon dioxide levels to rise significantly—which, he reasoned, would trap more of the sun's energy and make the earth hotter. For this reason, he used the example of a hothouse, or greenhouse, model to describe the warming of the planet.
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