Environment & Climate
Over time, great forces formed the earth’s features. Even today, the earth moves at faults, breaks in the earth's crust, its outermost layer. Earthquakes, volcanoes, weathering, erosion, and the buildup of sediment continue to reshape the surface. As a result, the earth offers a variety of types of land, water, and climates. For many people, environmental variations are the key reasons for travel.
Thirty percent of the earth is land. The land has been divided into seven continents. From largest to smallest, they are Asia, Africa, North America, South America, Antarctica, Europe, and Australia. The Ural Mountains divide Europe and Asia along a line running south and then west from northern Russia. The term continent is imprecise. Some geographers put Europe and Asia together as one continent, Eurasia. Also, geographers use the term Oceania to refer not only to the thousands of scattered islands in the Pacific but also to Australia and New Zealand.
The edge of land that borders the ocean along a continent or an island is its coast, seacoast, or shore. Land actually extends outward beyond the coast, gently sloping underwater. The area where the sea meets the land is the continental shelf. Because a country’s legal jurisdiction is limited to its territory, countries claim as much of their continental shelves as they can. How much of the shelf falls under a country’s legal jurisdiction influences activities from fishing and oil drilling to when a cruise ship can open its casinos and shops.
An island is a body of land completely surrounded by water and above water at high tide. Geographers treat islands near a continent as part of the mainland; for example, Great Britain and Ireland are considered part of Europe. A group of islands clustered together is an archipelago (arc kuh PEL uh goh).
Here are other terms that describe the land:
- An isthmus is a narrow bridge of land that connects two large landmasses. The Isthmus of Suez joins Africa to Asia. The Isthmus of Panama joins North and South America.
- A peninsula is land that extends from a continent and is almost surrounded by water. Florida is a prime example.
- A reef is a ridge of rocks or sand at or near the surface of the water along the coast. Coral reefs are ridges built by tiny sea animals called corals.
- A panhandles is a narrow projection of a larger territory into another’s land surface. In the United States, Florida, Texas, Oklahoma and Idaho have panhandles.
Features of the Land
Although each continent is unique, all share two basic features. First, each has old, geologically stable regions called shields. A shield is an area of the earth's crust that formed during its early history. Shields are relatively flat regions usually found in the continent’s interior.
Second, each continent has younger, more active regions marked by mountains. A mountain is a landform higher than its surroundings with some kind of peak or summit. North and South America have young, high mountain ranges (the Rockies and the Andes, respectively) rising near their west coasts. The steep, young Alps and the Himalaya extend eastward across Eurasia. The earth’s highest mountain is Mount Everest in the Himalaya; it soars 29,035 feet (8,850 m) above sea level. Older mountain systems, such as the Appalachians in eastern North America and the Urals of Eurasia, tend to be worn down and hence less steep.
Hills are more rounded and not as high as mountains. Valleys are the depressions between hills or mountains. Movements of the earth’s crust produce rift valleys, valleys that formed when the land sank between two parallel faults.
A canyon is a deep, narrow valley with steep sides. Canyons are generally created by water.
The fall line is the place near a continent’s edge where the land drops from a higher elevation to the coastal plain. Plains are flat or gently rolling lands. At the fall line, rivers generally have waterfalls or rapids. As a result, ships cannot navigate upstream unless a canal and locks are built.
Plateaus are another type of flatland. A plateau, also called a tableland, is higher than the surrounding land and has at least one steep side, called a cliff.
Water is the transparent liquid that forms the world’s oceans, rivers, and lakes. About 70 percent of the earth's surface is water. The location of navigable rivers and good harbours has shaped the flow of people, goods, and ideas from place to place. Most of the world’s great cities are built on or near water. When leisure time is available, people seek out water for recreation.
Ninety-seven percent of the earth’s water is found in the ocean, an interconnected body of salt water. The world ocean has four subdivisions: in order of size, the Pacific, Atlantic, Indian and Arctic. Each ocean includes smaller bodies of water called seas, gulfs and bays. A strait is a narrow passage of water that connects two larger bodies of water. For example, the Straight of Gibraltar connects the Atlantic Ocean and the Mediterranean Sea. Lagoons are narrow bodies of water that form between the mainland and barrier islands or reefs most are connected to the ocean by tidal inlets.
Tides, waves and currents move the ocean. Tides are the rhythmic use and fall of the ocean water that occur twice each day as a result of the gravitational pull of the moon and sun. Waves- movement on the ocean’s surfaces- are created by wind, not by ties. Currents are cold or warm rivers of water that flow within the ocean. Knowledge of surface ocean currents is essential for cruise lines because traveling with them reduces fuel costs.
Currents are caused by the rotation of the earth, moving air, and differences in water temperature within the ocean. The currents are of two kinds: some (thermohairne currents) flow from the ocean’s surface to the bottom and back; others (wind-driven currents) flow horizontally. The earth’s spin causes currents to curve to the right north of the equator and to the left south of the equator, a tendency known as the Coriolis effect.
Only about 3 percent of the earth’s water is fresh, not salty. Of fresh water, more than two-thirds is frozen in glaciers, huge masses of ice that move slowly over land. This movement formed the greatest number of the world’s lakes, bodies of water surrounded by land. Glaciers form lakes by cutting valleys and leaving deposits that dam the water formed by the glacier’s melting ice.
Other lakes form on karst, an area of land underlain by limestone that is honeycombed with sinkholes, underground streams, and caves. Karst is found throughout the world, but it is best developed in humid climates. In the United States, karst occurs in Missouri, Kentucky, Indiana, and Florida, areas of the country plagued by sudden sinkholes.
Lakes are of either salt or fresh water. Freshwater lakes that have both incoming and outgoing streams do not become salty; the Great Lakes between Canada and the United States are examples. At inland seas that have no outlets, water is lost by evaporation, and salt gradually builds up. Thus the Middle East's Dead Sea, the Caspian Sea, and Utah’s Great Salt Lake are very salty.
A river is a ribbon of water flowing over the land. Some rivers flow continuously; others flow intermittently. The beginning of a river is called its source or headwater. The source may be ice melting in a glacier, snow melting on a mountain, an overflowing lake, or a spring bubbling from the ground.
From its source, a river flows downhill. Streams, called tributaries, flow into the river. Where the river and its tributaries tumble over rocks and down steep bluffs, rapids and waterfalls occur. Downstream, as its slope levels out, the river begins to flow more slowly. It gradually widens and builds a broad floodplain. As it nears the ocean, the river may form a marsh. The end of a river is its mouth. Where a river empties into a larger body of water, it slows down, often dropping its sediment to form a fertile delta, a flat, low-lying plain at the river’s mouth Prime examples are the deltas of the Mississippi, Nile, Volga Ganges, Yangtze, and Mekong. Not all rivers have deltas. In some areas, powerful ocean waves and currents sweep material away as soon as it deposited. Other rivers do not carry enough sediment to form deltas.
In a few rivers, high tide sometimes begins with a tidal bore- an abrupt front of high water from the sea rushing up the mouth of a river. The Amazon has a tidal bore, but the bore of the Bay of Fundy in Canada is the most famous.
Note: Earthquakes and volcanoes under the ocean can cause a tsunami (sue NAHM ee), a wave that can move through the water at 400 mph (644 km) and reach a height of more than 100 feet (30 m) near the shore. Tsunamis are sometimes mistakenly called "tidal waves," but they have no connection with tides.
Weather and Climate
One of the first questions a traveler is likely to ask is “What will the weather be like there?” The most accurate answer you can give would be a description of a destination’s climate. Climate is the sum of weather over a period of time. Weather is what’s happening now. The positive characteristics of Hawaiis climate are what convinced you to vacation there. Rainy weather is what spoiled your golf game on the Tuesday you were there.
As the earth rotates around the sun, its tilt causes the seasons spring, summer, autumn, and winter—each with special light, temperature, and weather patterns that repeat themselves yearly. The seasons in the Northern Hemisphere are the opposite of those in the Southern Hemisphere, and not all parts of the earth have four distinct seasons.
Climates are also the products of (1) latitude, (2) elevation, (3) topography, and (4) distance from water. Each set of conditions forms a climate type.
Temperature is the degree of hotness or coldness as measured by a thermometer. The United States uses the Fahrenheit scale, but almost all other countries use the Celsius, or centigrade, scale. For most vacationers, a temperature below 64°F (18°C) is too cool for sitting around doing nothing; a temperature above 86°F (30°C) is too hot for active sport.
Atmospheric pressure is the weight of the atmosphere as measured by a barometer. Changes in pressure signal shifts in weather.
Wind is air movement caused by the uneven heating of the earth by the sun.
Humidity refers to how much water vapor the air contains. Most people find high humidity very uncomfortable.
Precipitation is rain, sleet, hail, or snow formed when water and winds interact with temperature.
Clouds consist of tiny water droplets or ice crystals. Cloudy days as a rule are cooler than clear ones. The opposite is true at night because clouds act as a blanket keeping the earth warm.
To understand how latitude affects climate, note that the sun’s rays reach the earth most directly at the equator. The farther you go from the equator, the cooler it is. The farthest points from the equator where the sun appears directly overhead are 23.5 degrees in either direction. These points are the Tropic of Cancer, the latitude line about 23.5 degrees north of the equator, and the Tropic of Capricorn, the latitude line about 23.5 degrees south of the equator. The lands between the Tropic of Cancer and the Tropic of Capricorn are known as the tropics.
In addition, latitude influences climate because winds vary with latitude. Trade winds are the winds that blow from the northeast toward the equator in the Northern Hemisphere and from the southeast toward the equator in the Southern Hemisphere. The westerlies are currents of air high above the earth that blow from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere. Westerlies steer storms from west to east across middle latitudes.
|Types of Climate Characterization|
|Tropical wet||Always hot and humid. Heavy precipitation|
|Tropical wet and dry||Always hot with alternate wet and dry seasons|
|Semiarid||Hot to cold. Light precipitation|
|Desert||Hot to cold. Very little precipitation|
|Subtropical dry summer||Hot, dry summers and mild, rainy winters|
|Humid subtropical||Warm to hot summers and cool winters|
|Humid oceanic||Warm summers and cool winters. Moderate precipitation|
|Humid continental||Mild summers and cold winters. Moderate precipitation|
|Subarctic||Short, cool summers and long, cold winters|
|Tundra||Always cold with brief chilly summers. Little precipitation|
|Icecap||Always cold. Precipitation almost always snow|
If latitude were the only variable that affected climate, generalizing would be easy. But other factors also shape climate. The higher a place is, the colder it is. For every 1,000 feet (304.8 m) in elevation, the temperature drops about 3.5°F (1.9°C). For example, Mount Kenya in Kenya—Africa’s second-highest mountain—is on the equator. It soars 17,058 feet (5,199 m).The climate is tropical at the base and polar on its twin peaks, where snow falls throughout the year. Global warming is melting the mountain’s glaciers.
Note that elevation and altitude are both measures of distance above sea level, but altitude refers to height in the atmosphere, and elevation refers to height on the surface of the earth.
The earth’s surface features also influence climate, particularly the development of clouds and precipitation. Mountains block or funnel the winds that bring clouds and rain. Lands on the leeward side of mountains- the protected side away from the wind- tend to be dry; they are said to be in a rain shadow. For example, eastern Washington State is in the rain shadow of the Cascade Range and is a semiarid region. On the western side of the mountains, Pacific winds bring ample rainfall, and the area is lushly forested. Some of the rainiest places on earth are on windward slopes, those facing the wind. The windward side of anything is the direction from which a wind is blowing.
Distance from Water
Water regulates climate because it is slow to change temperature. Winds blowing from the water bring cooler air in summer and warmer air in winter. Because an ocean’s water is warmest near the equator currents that begin there and flow north carry warm water. The Coriolis effect causes the water on the east coast of a continent to be warmer than the water on the west.
The Gulf Stream illustrates how a current influences climate. Its warm water originates in the western Caribbean and flows along the U.S. East Coast. It turns northeast after it reaches Cape Hatteras in North Carolina. There its path becomes twisted as it meets cold water from the north Some parts drift toward Europe and form the North Atlantic Drift. Thanks to the current’s lingering warmth, the British Isles and western Europe have a milder climate than has Canada’s province of Labrador on the same latitude Anther example is Peru, where the climate is cool due to the effect of the Humboldt Current.
Climate and vegetation have a close relationship. The worlds vegetation can be divided into four broad categories: forest, grassland, desert, and tundra. Forests of both evergreen and deciduous trees grow on every continent except Antarctica. About 5 percent of the earth is covered by rain forests. These are moist, densely wooded areas. Annual rainfall is about 80 inches (200 cm) and sometimes as high as 400 inches (1,000 cm). Vegetation in a rain forest consists of broadleaf evergreen trees, vines, and sparse undergrowth. The soil is typically shallow and nutrient poor. Once denuded, it does not renew itself easily. There are temperate as well as tropical rain forests. In the temperate rain forest, trees are lower and less dense than in the tropical rain forest, and there is more change with the seasons. Tropical rainforests have been called the “Jewels of the Earth” and the “World’s Larges Pharmacy” because more than one quarter of natural medicines have been discovered there. The term jungle is also sometimes applied to tropical rainforests.
Grasslands are flat or rolling open areas where grasses are the natural vegetation. Examples are the prairies of North America, the savannas of Africa, and the vast steppe that stretches in a wide band across much of eastern Europe and western and central Asia.
A desert is any region that supports little plant life because of insufficient moisture. The earth has cold deserts, such as the Arctic and the Antarctic, as well as hot ones. It is believed that no rain has fallen in Antarctica for 2 million years. In warm desert areas, underground water may provide an oasis, a small area of vegetation. About one-third of the world’s land surface is desert.
Tundra is a cold region characterized by low vegetation. There are two kinds: alpine tundra that is associated with high elevation, and Arctic tundra that exists primarily in extreme northern latitudes. Permafrost, a layer of permanently frozen ground beneath the earth’s surface, is a characteristic of Arctic tundra. Forests that begin south of the Arctic tundra are called taiga. Vast evergreen forests like those in Russia and Canada grow in the taiga area.
Major features of the earth include
✓ Continents, in order of size: Asia, Africa, North America, South America, Antarctica, Europe, and Australia.
✓ The world ocean, divided into the Pacific, Atlantic, Indian, and Arctic.
Climate reflects the interaction of
✓ Distance from water.