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Mojave National PreserveWorld Deserts World Deserts North American Deserts Protecting Deserts Home Desert lands cover incredible distances. Many who have driven through deserts in the United States may think they are enormous, but they are only the fifth largest in the world covering about 500,000 square miles. By contrast the great Sahara Desert covers almost 3.5 million square miles, the Australian deserts 1.3 million square miles, the Arabian deserts 1 million square miles, while the deserts of Turkestan have 750,000 square miles. Numerous smaller deserts are also scattered across the globe. All are unique, and have adapted to their own particular environments. Global Weather PatternsDeserts tend to occur in two belts that circle the globe. Both the Northern and Southern Hemisphere have this belt located between 15 and 35 degrees latitude, roughly centered over the Tropic of Cancer and the Tropic of Capricorn. This is no accident. The sun is more directly overhead the equatorial region so it receives the most intense sunlight, and this solar energy heats the air. Hot air has two important qualities: it can hold enormous quantities of moisture, and it rises up into the atmosphere. So hot tropical air tends to be moist and rise into the atmosphere. As this air rises it cools, condensing the moisture and converting it to water where it falls as rain. This is why rain forests tend to occur near the equator. What goes up must come down, and gravity pulls this mass of rising air back to the ground. Tropical air typically falls at about 30 degrees latitude on either side of the equator and along the desert belt, but robbed of its moisture it is now hot and dry. The result are often persistent high pressure systems that tend to block incoming storms, or push them into other regions. These patterns make deserts possible, but typically other factor must also intrude to make deserts a reality.

div#related-article-links p a, div#related-article-links p a:visited { color:#06c; } A leopard can, after all, change its spots: a new species of big cat has been identified for the first time in almost two centuries. The big cats prowling the jungles of Borneo and Sumatra had long been assumed to be the same clouded leopards that are found in mainland Asia. Genetic analysis and comparisons of fur patterns have now shown the two animals to be as distinct as the lion and the tiger, the WWF announced yesterday. Among the findings that convinced scientists was the realisation that the Bornean cat has changed the number and prominence of its spots.

The cats have now been reclassified as the Bornean clouded leopard, with the name Neofelis diardi, to distinguish them from other clouded leopards, Neofelis nebulosa. The two species, both endangered, are shown by genetic analysis to have separated 1.4 million years ago, after the animals used a land bridge, now covered by water, from mainland Asia to reach Borneo and Sumatra.

American History: Life in the US After World War Two