Deserts, Revised Edition

Peter Aleshire

Description

Complete with vivid, dramatic photographs, this eBook presents an oasis of information on the world's starkest deserts. Journey from Death Valley, the lowest point in North America, to the Libyan desert, the hottest on Earth, where temperatures can reach 136°F, to Antarctica’s vast polar deserts, which have not had ice cover for thousands of years. From trade wind and rainshadow deserts to interior and coastal deserts, Deserts, Revised Edition spotlights 10 superlative examples and reveals why these astonishing landforms are never static but always changing.

Sujets

• Science de la Terre
• Science
• Nature
• Formation
• Global
• Désert
• Climate
• Geology
• Environment
• Desert
• Sciences et techniques
• Young Adult Nonfiction
• Earth Sicences

Informations

• Publié par: Infobase Publishing
• Date de parution: 01 juin 2019
• Nombre de lectures: 0
• EAN13: 9781438182568
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Deserts, Revised Edition
Copyright © 2019 by Peter Aleshire
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For more information, contact:
Chelsea House An imprint of Infobase 132 West 31st Street New York NY 10001
ISBN 978-1-4381-8256-8
You can find Chelsea House on the World Wide Web at http://www.infobase.com
Contents Chapters Deserts Sonoran Desert Mojave Desert Great Basin Desert Chihuahuan Desert Sahara Desert Arabian Desert Kalahari Desert Australian deserts Gobi Desert Atacama Desert Support Materials Glossary Index
Chapters
Deserts

The appearance and evolution of Earth's deserts offer deep insights into geology, history, evolution, climate, and the whole rich history of the planet. Although deserts now cover great swaths of Earth's surface along the broad, hot midsection of the planet, most modern deserts are new landscapes—places where grasslands and woodlands have been transformed into an austere and revealing terrain that makes special demands of any living creatures who brave it and often thrive.
The deserts of North America may seem vast in their sprawl across more than 500,000 square miles (1.3 million sq km), but they are dwarfed by the 3.5 million square miles (7.8 million sq km) of the Sahara Desert, the 1.3 million square miles (3.4 million sq km) of the Australian deserts, and the 900,000 square miles (2.3 million sq km) covered by the Arabian deserts. 
Generally defined as an arid or dry area where annual evaporation from the surface exceeds annual rainfall, deserts are the result of a combination of position on the globe, local terrain, and global atmospheric circulation. Most of the deserts of the world lie between 15 and 30 degrees latitude, generally centered over the tropic of Cancer and the tropic of Capricorn. This midsection of the planet receives the most annual sunlight. The energy from the sun heats the air, especially along the equator. This heated air can hold an enormous amount of water. As it rises, much of that water condenses into clouds, which rain down upon the narrow belt of tropical rain forests along the equator, generally about 30 degrees latitude on either side of the equator. Now wrung out, the dry air moves both north and south, cooling as it moves. Eventually, it is cold and heavy enough to descend back down to the surface, creating the dry, wind-prone zones in which deserts can form.
Deserts formed by this global circulatory pattern are known as subtropical deserts. But other factors can combine to create the perfect conditions for a major desert. As a result, the world's deserts fall into five major types. 
Subtropical Deserts
The enormous Sahara Desert that covers most of northern Africa is a subtropical desert, formed by the global circulatory pattern described above. Another desert of this type is the Kalahari Desert in southern Africa. Both of these deserts receive the sinking, cool dry air that has completed its journey away from the equator, which means very few clouds form to bring moisture to the parched earth. The Sahara Desert receives an average of only 3 inches (76.2 mm) of rain each year.  
Coastal Deserts
Coastal deserts form on the western edge of continents near the tropic of Cancer and the tropic of Capricorn largely as a result of great currents in the ocean. These great rivers in the ocean move in a great clockwise pattern in the Northern Hemisphere and in a counterclockwise direction in the Southern Hemisphere. Some of those currents start at the poles as heavy, chilled water sinks and flows along the western edges of the continents toward the equator. However, on the eastern edge of most of the continents, those currents flow in the opposite direction, moving warm tropical water toward the frigid poles. The cold currents that flow along the west side of most continents do not release water easily to the atmosphere, which means that the coastal areas next to such currents are often starved for water. This helps explain the high, cold, desperately dry Atacama Desert of Chile, which lies on the South American coast opposite the lush rain forest interior of Brazil. Known as the driest place on Earth, the Atacama Desert also lies in the rain shadow of the towering Andes Mountains. 
Rain Shadow Deserts
Many deserts form in low-lying regions that lie in the rain shadow of a major mountain range. Often, such desert-forming mountain ranges lie near coastal regions. For example, California's Mojave Desert is located in the rain shadow of the Sierra Nevada mountains. When moisture-laden air moves inland off the ocean, it encounters the barrier of the mountains. As the moist air rises to move over the mountain range, it cools enough that it can no longer hold all that moisture. The water falls as rain and snow on the mountains so that by the time the air moves into the low-lying regions beyond, it is dry and thirsty. To one degree or another, this rain shadow effect has created all of the deserts of North America.
Interior Deserts
Another type of desert forms in remote, interior regions, so far from the ocean that they are cut off from a ready supply of atmospheric water. Water from the warm tropics or the wet oceans that enters the atmosphere drops out as rain long before it reaches these vast interior spaces, including the dry, barren 1,000-mile- (1,609-km-) long Gobi Desert of China and Mongolia. 
Polar Deserts
It may be surprising to learn that the world’s largest deserts are located at two of the coldest places on Earth: Antarctica and the Arctic. Deserts are not defined by heat, they are defined by dryness or a lack of moisture. So a desert can be hot or cold. The Antarctic Polar Desert is 5.5 million square miles (1.4 sq km) in size, nearly covering the entire continent of Antarctica. The Arctic Polar Desert is about the same size, 5.4 million square miles (1.3 sq km), and extends over parts of Alaska, Canada, Greenland, Iceland, Norway, Sweden, Finland and Russia. There is lots of water locked up in ice in the polar deserts, but very little of it is available for animals and plants. The average annual precipitation that falls mostly as snow in Antarctica is about 6.5 inches (166 mm). 
Desertification: A Global Crisis
Human activities such as deforestation, non-sustainable farming, and overgrazing by livestock are causing deserts to form where once-fertile land existed. This process of transforming productive land into desert is known as desertification. It is happening around the world as the population continues to grow and people put increasing demands on the land. 
Deserts are not just barren wastelands of sand. They are home to as many as one billion people worldwide and many unique plants and animals. Desertification occurs when vegetation is stripped from land, making it unfertile and unusable for farming. There are two main causes of the loss of vegetation: drought caused by climate change and human actions such as aggressive farming, overgrazing of farm animals, and cutting down trees. Climate change is exacerbating the negative impacts of desertification. Rising global temperatures lead to drought and an increased in wildfires that destroy slow-growing desert trees and shrubs. 
A new edition of the Atlas of Desertification , published in June 2018, found that more than 75 percent of the Earth’s land has been degraded and that amount could increase to 90 percent by 2050. Africa and Asia are feeling the greatest impact as worldwide an area half the size of the European Union, 1.6 million square miles (4.2 million square km), is degraded each year. If the rate of desertification continues, global crop yields are predicted to be 10 percent lower by 2050, particularly in India, China, and sub-Saharan Africa.
There are solutions. Sustainable farming practices, a shift to plant-based diets (reducing the amount of land needed for livestock grazing), and a reduction in food loss and waste could help reduce the pressure on agricultural land.
The locations and dynamics of the world's deserts illuminate vital questions about everything from the positions of the continents to the workings of the climate of the entire planet. For instance, the dramatic increase in the extent of deserts worldwide in recent centuries holds important clues about the impact of human beings on the environment and future shifts in climate.
All of which makes understanding the history, evolution, dynamics, and geology of the deserts essential to understanding the history and fate of both the planet and human beings.
Sonoran Desert

The defining plant of the Sonoran Desert, the largest of the saguaro cacti are 200 years old, 50 feet high (15.24 m), and weigh eight tons. They dominate the park that occupies two sprawling areas of desert on either side of Tucson. This towering plant is perfectly adapted to desert conditions with its backwards photosynthesis, stubborn persistence in the face of drought, and ability to store tons of water gathered after the infrequent but fierce desert rainstorms. In turn, the saguaro supports diverse desert ecology and has sustained ancient civilizations. It provides a vital resource for desert birds like the white-winged dove, Gila woodpecker, flicker, and elf owl, not to mention an intricate network of insects, lizards, and bacteria that take full advantage of its rich production of seeds, its sweet fruit, and its ability to store vital moisture through months and then years of drought. Moreover, its surprisingly recent adaptation to desert conditions and spread from its isolated Ice Age sanctuaries throughout northern Mexico and southern Arizona have in the process largely defined the extent of the Sonoran Desert, which remains the most diverse and productive of the world's deserts.
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