The United States is a country of contrasts: of snow covered peaks and
sprawling deserts, of densely packed cities and uninhabited wilderness, of enormous
riches and terrible poverty. It includes some of the coldest, hottest, driest, wettest,
and windiest places
on Earth. The sheer size of the United States has been an
important influence on how Americans think and act.
Throughout the country's
history, there has been a new frontier for Americans to explore, whether in science and technology, world politics, or the arts. The hard work and pioneering spirit of immigrants from every corner of the world helped build the country and create a melting pot of races and ethnic groups.
Geography
The United States is the fourth largest country in the world and includes a wide range of terrain and climates. It is made up of fifty states, including Alaska, which lies to the north of Canada, and Hawaii, an archipelago in the Pacific Ocean. The forty eight states in North America occupy an area of 3,787,300 square miles (9,809,107 square kilometers) bound by the Atlantic and Pacific Oceans, the Canadian border, and Mexico.
Forested coastal plains border the eastern seaboard, ending at the lower slopes of the Appalachian Mountains, which extend from Alabama to Maine. To the west of the Appalachians are the great central plains. Originally vast prairies filled with herds of wild buffalo, the plains are now the country's farm belt, where wheat and corn are grown. The central plains end at the foothills of the Rocky Mountains, which stretch from New Mexico to Canada and Alaska. The soaring peaks of the Rockies are snowcapped all year round, even in the southern ranges. West of the mountain range are the western plateaus and the Grand Canyon, one of the world's natural wonders. The Pacific ranges run along the west coast and into Alaska, where Mt. McKinley, the nation's highest peak, is found. The west coast is subject to earthquakes. Located near the San Andreas Fault, a major fracture in Earth's crust, San Francisco experienced major earthquakes in 1906 and 1989.
There are six great rivers in the United States: the Mississippi, Missouri, Ohio, Columbia, Colorado, and the Rio Grande. The Mississippi is the longest river in North America and an important artery of trade. It travels 2,350 miles (3,781 km) from Lake Itasca in Minnesota to the Gulf of Mexico, near New Orleans. The Colorado, a rapid, dangerous river, races through the southwest before slowing down at the Grand Canyon. Dams on the Colorado have helped turn the surrounding area into fertile farmland. The Rio Grande forms the border between Texas and Mexico and is also used for irrigation. The Columbia, which runs along the Washington and Oregon border, is one of the world's greatest sources of hydroelectric power. In the past, it was noted for its abundance of salmon, but pollution and the construction of modern dams have greatly reduced its marine life in recent years.
USA Climate
Climate varies widely in the United States, from the wet Pacific Northwest to the deserts of Arizona and Nevada, from the bitter winters of North Dakota and Minnesota to balmy, tropical Florida. In fact, visitors from almost anywhere in the world would be able to find somewhere in the country that would remind them of home.
Four Seasons
Except for Alaska, which experiences severe cold throughout the year, most of the country falls in the temperate climate zone, with four seasons in a year. Autumn begins in late September and ends in December. The northern Midwest is hit hardest by winter cold. Hurricanes are a problem in the coastal areas of the eastern and southern United States, while tornadoes plague the Midwest. Along the western coast, warm Pacific Ocean currents keep the climate mild all year round. Temperatures in the deserts of the Southwest are high during the day but drop in the evening.
Plants and Animals
Due to the variation in climate and topography, the United States has a tremendous variety of flora and fauna. Although many large cities dot the country, there are also vast, scarcely inhabited areas. New England is famous for the striking colors of its trees in autumn, when leaves turn from green to brilliant hues of red and gold. The southeastern regions are known for their beautiful fruit trees. Florida has mangrove swamps filled with alligators. Southwestern areas are characterized by desert type vegetation. Forests cover the northwestern coastal regions. Perhaps most stunning are the forests of giant redwood trees along the northwestern coast.
The United States is home to many thriving species of animals. Deer live in forested areas, and bears roam the national parks. The bald eagle, however, is a threatened species, and the condor is endangered. Conservation groups have organized to protect them. The indigenous buffalo, which once roamed the Great Plains in large herds, has been hunted close to extinction.
Extract from "Countries Of The World - USA". Written by Elizabeth Berg. Times Editions Pty Ltd 1999.
Global Warming
Global warming is the gradual rise of the earth’s near-surface temperature
over approximately the last hundred years. The best available scientific
evidence—based on continuous satellite monitoring and data from about
2,000 meteorological stations around the world—indicates that globally averaged
surface temperatures have warmed by about 0.3 to 0.6°C since the late
nineteenth century. Different regions have warmed—some have even
cooled—by different amounts. Generally, the Northern Hemisphere has
warmed to a greater extent than the Southern Hemisphere, and mid to high
latitudes have generally warmed more than the tropics.
Since the advent of satellites, it has become possible for scientists to thoroughly
monitor the earth’s climate on a global scale. To examine the historical
climate record, however, scientists have to use earlier, sparser forms of
measurement, such as long-standing temperature records and less exact
“proxy” data, such as the growth of coral, tree rings, as well as information
from ice cores, which contain trapped gas bubbles and dust grains representative
of the climate in which they were deposited. The bubbles in these cores
contain oxygen, particularly oxygen isotopes 180 to 160, which are sensitive to
variations in temperature. From the ratio between these isotopes at varying ice
depths scientists can reconstruct a picture of the temperature variations over
time in specific locations. Greater measurement uncertainty surrounds the
earlier parts of this record because of sparse coverage (especially in ocean
regions). Despite this uncertainty, the balance of scientific evidence confirms
that there has been a discernable warming over the last century.
Causes
Gases such as water vapor, methane, and carbon dioxide allow short-wave
radiation from the sun to pass through to the surface of the earth, but do not
allow long-wave radiation reflected from the earth to travel back out into
space. This naturally occurring insulation process—dubbed the greenhouse
effect—keeps the earth warm: In its absence, the earth would be about 33°C
cooler than it is now. However, as the concentration of greenhouse gases
increases (due largely to human activities), most scientists agree that the
effect is expected to intensify, raising average global temperatures. However, the earth’s climate is known to vary on long timescales. The
existence of naturally occurring ice ages and warm periods in the distant past
demonstrates that natural factors such as solar variability, volcanic activity,
and fluctuations in greenhouse gases play important roles in regulating the
earth’s climate. A minority of scientists believe that purely natural variations
in these factors can account for the observed global warming.
Climate in the Twenty-first Century
Climate forecasts are inherently imprecise largely because of two different
sorts of uncertainty: incomplete knowledge about how the system works—
understandable for a system governed by processes the spatial scales of which
range from the molecular to the global and uncertainty about how important
climate factors will evolve in the future. A variety of factors affect temperature
near the surface of the earth, including variability in solar output, volcanic
activity, and dust and other aerosols, in addition to concentrations of
greenhouse gases.
However, this uncertainty does not stop one from making some broad
statements about (1) the likelihood of the sources of observed global warming
and (2) the likely effects of continued warming. In the first case, attempts by
climate modelers to reproduce the observed global near-surface temperature record using only natural variability in climate models have proved inadequate.
The Third Assessment Report (2001) of the Intergovernmental Panel
on Climate Change (IPCC) attributes some 80 percent of recent rises in
global temperature to human activities, with other important contributions
coming from volcanic and solar sources. Over the coming century, likely
effects of continued warming include higher daily maximum and minimum
temperatures, more hot days over most land areas, fewer frosts in winter,
fewer cold days over most land areas, a reduced daily range of temperatures,
more extreme precipitation events (all very likely), increased risk of drought,
increases in cyclone peak wind, and precipitation intensity (likely). Other
effects, such as the disintegration of Antarctic ice sheets, carry potentially
enormous implications, but are considered very unlikely.
