Download Earth_Day - Caldwell County Schools

1. Earth Day
On April 22, hundreds of millions of people in the United States, Canada, and more
than 190 other countries will celebrate Earth Day. On this day, people everywhere
come together with a single goal: to protect the health of our planet. Schools and
community groups hold recycling drives. People work in teams to clean up parks
and beaches. Others leave their cars at home on Earth Day, turn off lights and
appliances, and otherwise avoid consuming energy or creating pollution. Most of all,
Earth Day has been a very effective means for highlighting the greatest
environmental issues of our time: climate change, energy efficiency, renewable
energy, and the creation of a global green economy.
2013 is the 43rd year in a row that the world has paused to observe Earth Day.
Earth Day is celebrated annually on April 22 to focus attention on the protection
and conservation of natural resources. Arising from a student-led movement in the
United States, Earth Day gained status and stature when, in 1969, U.S. senator
Gaylord Nelson supported the notion that a day be set aside to honor the
environment and to remind humankind of the importance of environmental
protection.
Now celebrated worldwide, Earth Day is marked by official and unofficial activities,
large and small. Many government bodies and international organizations, including
the United Nations, use the occasion to highlight programs, research reports, and
problems—and their solutions—related to the world's natural environment.
2. Environmental Movements: Introduction to Environmental Movements
Environmental movements are social and political movements that are concerned
with the protection of natural surroundings from depletion, pollution and
degradation by humans. They are primarily a post–Industrial Revolution
phenomenon initiated mainly in the United States and Europe by educated
members of society—scientists, politicians, economists, academicians—following
major spurts of industrial expansion and resource exploitation. Such movements
initially focused on population growth and resource depletion, but more recently
they have been concerned with human-generated pollution (see pollution,
environmental) and the preservation of natural environments. Three major
environmental movements of the past 200 years are described below.
3. Environmental Movements: Malthus, Ricardo, and Mill
Thomas Robert Malthus and David Ricardo were English economists who lived
during the early years of the Industrial Revolution. They watched as plummeting
death rates transformed Europe from an agrarian society to one more urban and
more densely populated. Malthus put forth his ideas regarding the future of this
technologically sophisticated yet crowded new world in his monumental treatise of
1798 entitled An Essay on the Principle of Population as It Affects the Future
Improvement of Society. He believed that population would eventually outstrip food
supplies with calamitous results. Only disease, wars, and voluntary reductions in
birthrates could save the world. Ricardo wrote along similar lines in his 1817 book
Principles of Political Economy and Taxation. Some 30 years later, political theorist
John Stuart Mill wrote Principles of Political Economy (1848). Mill believed that
humanity might be able to check population growth while discovering and better
utilizing resources, but he also introduced the notion that personal solitude and
natural beauty might be impaired through population and industrial growth.
During the remainder of the 19th century, public interest in natural environments
was further stimulated by such writers as Henry David Thoreau (Walden, 1854) and
George Perkins Marsh (Man and Nature, 1864).
4. Environmental Movements: The Conservation Movement
An American event that spanned the period 1890 to 1920, the conservation
movement was closely identified with the personality and politics of President
Theodore Roosevelt. By the end of the 19th century, Americans were concerned
with the rapid pace of social progress. They had seen the United States move
quickly from a frontier to an industrial society, and the nation's much-cherished
natural resource endowment, especially its forests, appeared on the verge of
extinction. Under Roosevelt's programs, the protection of forests, rangeland, and
mineral and water resources began to evolve in piecemeal fashion. Perceiving this
approach as inadequate, administration officials, such as Chief of the U.S. Forest
Service Gifford Pinchot and Secretary of the Interior James R. Garfield, argued for a
more unified policy of natural-resource planning. A successful appeal was made to
the public for political support, and the drive for resource protection surged forward
among middle- and upper-income Americans with the fervor of a moral crusade.
Some people, such as the naturalist-founder of the Sierra Club, John Muir, favored
resource preservation. The prevailing theme of the era, however, was one of
conservation—the restrained and efficient use of natural resources. American
businessmen were generally supportive. The conservation movement's goal—to
provide for the sustained production of material goods at the lowest cost—was very
much in tune with business thought of the time.
The most significant legacy of the conservation movement was its application of
science to natural-resource management problems, through programs administered
by the federal bureaucracy. Just as philosophy had aided the earlier British
economists, practical science was the ally of the conservation movement. In order
to administer scientifically based management, major federal and state
conservation laws were passed, and new agencies such as the U.S. Forest Service,
the United States Geological Survey, the National Park Service (see national parks),
and the Bureau of Reclamation were created.
By 1920, political squabbling among the various participants, and changes in
presidential administrations, had slowed the momentum of the conservation
movement. Over the next three decades the Depression of the 1930s and World
War II dominated American energies, and ideas about preserving nature seemed to
have lost their relevance.
5. Environmental Movements: The Modern Environmental Movement
The publication of Silent Spring by Rachel Carson in 1962 provides a notable event
by which to mark the beginning of the modern environmental movement. Carson, a
successful author and former U.S. Fish and Wildlife Service biologist, wrote about
the dangers of such recently developed agricultural chemicals as DDT, sending the
world very specific warnings about the risks of postwar technologies that were
producing artificial pesticides and other new chemical products.
Silent Spring inspired others to write about the threats that human actions posed to
the environment. Notable examples of these writings include Paul Ehrlich's The
Population Bomb (1968), Barry Commoner's The Closing Circle (1971), and Limits
to Growth (1972), written by a research team from the Massachusetts Institute of
Technology.
Carson's works, and those which followed, engendered almost immediate
grassroots sentiment for improving environmental quality. Support for change was
perhaps nowhere stronger than on college campuses, where environmental issues
often became intertwined with other concerns, such as protests against the
Vietnam War. Earth Day, first held Apr. 22, 1970, was largely a campus-based
event that represented perhaps the apogee of the early years of the movement.
The heightened social concern led to the passage of important environmental
legislation. These laws included the National Environmental Policy Act of 1969, the
Clean Water Act of 1972, the National Forest Management Act of 1976, the Clean
Air Act amendments of 1977, and the National Acid Precipitation Act of 1980, as
well as the creation (1970) of the Environmental Protection Agency. The National
Environmental Policy Act was particularly important. It established a process that
forced federal agencies to examine the impacts that all their activities, such as dam
and highway construction, could have on the environment. Today federal agencies
routinely produce hundreds of environmental impact statements, which help to
identify courses of action that will minimize adverse impacts on the environment.
By the 1980s, public interest in the environment was further strengthened by a
number of events such as the acid rain controversy, the Chernobyl nuclear
catastrophe, the Exxon Valdez disaster (see also oil spill), tropical deforestation, the
harvesting of old-growth timber in Alaska and the Pacific Northwest, the depletion
of the ozone layer, and the discovery of the possibility of global warming.
Many organizations are now involved in the environmental movement. Among the
most notable are the Sierra Club, the Wilderness Society, the National Audubon
Society, the Natural Resources Defense Council, the National Wildlife Federation,
the Izaak Walton League of America, and Environmental Defense. Individual groups
tend to specialize in particular environmental issues. They rely upon fund raising,
lobbying, the political system, and the courts. In addition to these mainstream
groups, there are radical environmental groups such as Earth First!, and
Greenpeace International, which sometimes use confrontational techniques such as
driving hidden metal spikes into forest trees, to prevent them from being processed
in saw mills, and harassing whaling ships from small boats. "Deep ecology" is the
motivating philosophy of many radical environmentalists. This philosophy embodies
the notion that all of nature's creations are deserving of equal protection, and thus
direct action must be taken to protect them. Political Green parties have also been
formed, most notably in Europe, to support environmental candidates for political
office.
The modern environmental movement differs from earlier movements in that the
concern is over human-caused pollution and degradation of the environment as well
as population growth and resource scarcity. Also, many of the environmental
problems faced today are global as well as local. However, despite apparent public
interest in the environment, at least in the Western world, the barriers to a better
environment seem formidable. The lack of progress on the resolutions of the United
Nations–sponsored 1992 Earth Summit and on the 1997 Kyoto Protocol to minimize
global climatic change are testimonies to the difficulties involved. The United States
actually rejected the latter in 2001, while the activating signature (Russia) did not
materialize until 2004; implementation of the protocol is still to be decided.
Developing future consensus among the nations of the world and coordinated plans
of action to combat environmental degradation, excessive population growth, and
resource depletion will be quite challenging.
6. Conservation: Introduction to Conservation
Conservation is the philosophy and policy of managing the environment to assure
adequate supplies of natural resources for future as well as present generations. In
the late 1800s and early 1900s, conservation usually referred to management of a
single, economically valuable resource such as forests, soils, or wildlife. Today,
reflecting an increasing understanding of ecology—the science of the
interrelationships between living things and their environment—the use of the term
conservation has been extended to consider the environment as a whole. Modern
conservation, then, can be defined as the management of the human use of the
environment so that it may yield the greatest sustainable benefit to present
generations while maintaining its potential to meet the needs and aspirations of
future generations. It is concerned with the quality as well as the basic support of
human life. Conservationists recognize that human activities profoundly change the
face of the Earth and can irreparably damage or destroy the natural resources on
which human well-being and, indeed, human survival depend.
Natural resources traditionally have been classified as renewable and
nonrenewable. Renewable resources are those which, under proper management,
regenerate and even improve their resource values, but which when misused can
be depleted or lost entirely. They include plants and animals and other resources
such as soils and inland waters. Nonrenewable resources are minerals and fossil
and nuclear fuels, which are present on the Earth in fixed amounts and, once used,
do not regenerate. Increasingly, elements of the environment, such as oceans, tidal
lands, and the air itself, are also being recognized as natural resources.
It has become increasingly clear that resources and resource uses are intimately
interrelated. A forest contains lumber, which is a valuable economic commodity; it
also, however, serves as a watershed, keeps soil from eroding, provides habitat for
wildlife, provides recreation, and ameliorates local climate. Indiscriminate cutting of
trees may destroy the forest, but it will also have corollary, and potentially far more
serious, effects. A paramount principle of conservation is that the use of any
resource requires consideration of the impacts of that use on associated resources,
and on the environment as a whole.
The goals of resource conservation are 1) the maintenance of essential ecological
processes, which range from the global cycles of nitrogen (see nitrogen cycle),
carbon dioxide, and water to the localized regeneration of soil, recycling of nutrients
(see nutrient cycle), and cleansing of waters and air and life-support systems, such
as agricultural systems, coastal and freshwater systems, and forests; 2) the
preservation of genetic diversity; and 3) the assurance that utilization of species
and ecosystems such as forests and grazing lands is sustainable. The consumption
of nonrenewable resources should ensure that scarce minerals are used
conservatively and recycled where possible, and that their mining and use have the
least possible adverse impact on other resources, and on environmental quality.
7. Conservation: History: The United States
The conservation movement began in the United States largely in response to the
unparalleled damage the settlers had inflicted on natural resources. The original
vast forests of eastern North America were devastated by clearing for agriculture,
and by destructive lumbering and the massive forest fires that followed. Agricultural
soils were depleted, farmers speaking proudly of having "wore out" several farms
on their march westward. The grasslands of the west were so severely overgrazed
that many have never recovered their productivity. Wildlife was particularly hard hit
by unrestricted market hunting and predator control. The abundant herds of bison,
deer, elk, and antelope were greatly reduced, and wolves, bears, and mountain
lions were virtually eliminated. A number of local varieties of wildlife vanished
utterly. Some bird species were virtually wiped out, and species that had existed in
incredible numbers—the passenger pigeon and Carolina parakeet—were
exterminated.
Conservation in America grew out of the recognition of these destructive processes.
Many far-sighted individuals contributed to conservation theory. In 1832 artist and
author George Catlin proposed setting aside large areas of the western United
States where the Indians, as well as wildlife, could survive. Geographer George
Perkins Marsh published Man and Nature (1864), the first real consideration of the
human impact on nature and its resources. Author and naturalist John Muir became
a champion of wilderness preservation and was a founder and first president of the
Sierra Club.
The later 1800s saw the creation of several of the earliest private conservation
organizations. In 1875 the American Forestry Association was founded, followed in
1883 by the American Ornithologists' Union, the Boone and Crockett Club in 1887,
the Sierra Club in 1892, and the New York Zoological Society in 1895. These were
pioneers among the nongovernmental organizations that have played a vital role in
the development of conservation.
8. The Beginnings of Federal Involvement.
In 1864, Congress gave the state of California Yosemite Valley for a public park and
recreation area, effectively making it the precursor of today's national park system;
in 1872, it established Yellowstone as America's first true national park. The
Division of Forestry, now the U.S. Forest Service, was created in 1876. The U.S.
Geological Survey was established in 1879, and its first director, John Wesley
Powell, publicized the agricultural possibilities and limitations of the West. The U.S.
Biological Survey, precursor of the Fish and Wildlife Service, was founded in 1885.
In 1897, Gifford Pinchot was appointed chief of the reorganized Division of Forestry.
Pinchot became a key architect of the conservation policies that developed under
President Theodore Roosevelt.
9. The Roosevelt Administrations.
Conservation of natural resources was firmly established as an important concern
and priority of the federal government under Theodore Roosevelt's administration
(1901–09). Through various initiatives, including the White House Governors'
Conference on Conservation held in 1908, Roosevelt also persuaded state
governments of the importance of conservation.
The establishment of national parks, national forests (see National Forest System),
and wildlife refuges (the first in 1903) firmly set out the conservation principle that
certain public lands must be held in trust by the federal government and managed
for the good of the country as a whole. For a time, other lands in the public domain
received little attention, but in the 1930s it became evident that resource depletion
due to overgrazing on these lands had reached crisis proportions. With the passage
of the Taylor Grazing Act (1934), under President Franklin D. Roosevelt, Congress
affirmed that all lands in the public domain were to be managed as part of the
public trust.
The catastrophe known as the Dust Bowl occurred in the early 1930s, when a series
of dry years coincided with the extension of agriculture to unsuitable lands, and
when poor agricultural practices had caused grossly deteriorated conditions on vast
areas of midwestern and western farm lands. Dry and denuded lands simply blew
away, and the clouds of dust reached as far east as Washington, D.C., dramatizing
the severity of the crisis. With the establishment (1933) of the Soil Erosion Service,
the country began to accept the principle that it was appropriate for the
government to intervene to assist private landowners, especially in the areas of soil
and water conservation. The year 1933 also saw the creation of the Civilian
Conservation Corps and the Tennessee Valley Authority.
10. Post World War II.
In the period following World War II, growing populations, advanced technological
capabilities, and increased emphasis on economic development put new stresses on
the environment and its resources. For example, DDT and other synthetic pesticides
were developed in an attempt to reduce insect-borne diseases in humans and to
increase food production. The initial results were dramatically successful. DDT was
heavily used virtually worldwide, and in many areas malaria, carried by the
anopheles mosquito, practically disappeared. Particularly in the United States, the
new pesticides helped to produce bumper crops. Nevertheless, it became apparent
that these substances were producing severe environmental effects, and in many
cases creating problems that were worse than those the pesticides were intended to
cure. The publication in 1962 of Rachel Carson's Silent Spring alerted Americans to
the dangers of unwise pesticide applications, and eventually the use of DDT and
related pesticides was severely restricted.
11. The Emergence of Environmentalism.
As pollution increased throughout the 1950s and '60s, conservation problems were
forcibly brought to public attention via television. People saw the ghastly effects of
mercury poisoning at Minamata Bay in Japan in the 1950s, the Torrey Canyon oil
spill (1967) in the English Channel, and the killer smog episodes in Los Angeles and
London. One result was an unprecedented growth of public concern and the
emergence of citizen conservation organizations. Many came to recognize that the
narrow approaches to conservation that had marked earlier efforts were no longer
appropriate and that a more comprehensive environmental approach was needed.
Conservationists began to become environmentalists.
Public environmental concerns led Congress to develop the National Environmental
Policy Act of 1969 (NEPA) and to pass it unanimously over President Richard M.
Nixon's objections. In the process of developing NEPA, Congress found that there
were more than 80 government units whose activities affected the environment, yet
there was no governmental mechanism to develop environmental policy, maintain
an overview of governmental actions, or provide environmental coordination. To fill
these needs, NEPA established the Council on Environmental Quality and mandated
the environmental impact statement in an attempt to ensure that environmental
factors received due consideration in any federal actions. Today, most states, many
other countries, and international development institutions have adopted somewhat
similar mechanisms to assess the environmental effects of proposed actions.
The 1970s represent the high point in the passage of U.S. conservation-related
legislation. Following NEPA and the establishment of the Environmental Protection
Agency in 1970, a series of important pollution control measures were legislated:
the Clean Air Act of 1970, the Water Pollution Control Act of 1972, the Toxic
Substances Control Act of 1976, and the Clean Water Act of 1987, as well as
comprehensive legislation on ocean dumping, fisheries conservation and
management, wetlands and coastal-zone conservation, and protection of marine
mammals and endangered species.
The International Environment Protection Act of 1983 is landmark legislation. It
incorporates wildlife and plant conservation as important objectives of U.S.
development assistance to developing countries, and it requires the federal
government to formulate U.S. strategy to conserve biological diversity in those
countries.
The 1980s were marked by a backlash against the environmentalism of the
previous decade. Led by the administration of President Ronald Reagan and based
on ideological, political, and economic concerns, attempts were made to weaken or
repeal many of the conservation-related laws and regulations of the previous
decade. Outspokenly anticonservation administrators were appointed to head
government agencies such as the Department of the Interior and the EPA, and
antienvironment citizen groups such as Wise Use Movement emerged. This in turn
led to a revitalization of the environmental movement, and the country has made
some additional progress on environmental issues, but conservation-related
matters often have remained controversial.
12. Conservation: International Conservation
The most effective early international conservation efforts involved agreements on
migratory species, such as the 1911 treaty for the conservation of the northern fur
seal (signed by Canada, Japan, Russia, and the United States) and the 1916 U.S.Canadian treaty for the conservation of migratory waterfowl. Only since World War
II, however, has public awareness led to increasing international cooperation on
such conservation issues as endangered species, national parks, conservation
education, and conservation law. The United Nations Conference on the Human
Environment, held in Sweden in 1972, firmly established conservation of natural
resources as an important concern of governments throughout the world.
Today, conservation is concerned with a small number of major global issues. Each
of these affects the others, and all are basic to human survival. Although not
strictly conservation issues, population growth and economic factors underlie
virtually all conservation problems.
13. Deforestation.
Tropical forests are being destroyed at an ever increasing rate. Estimates of the
extent and rate of loss vary, but it appears that nearly half of the world's tropical
forests already have been lost, and the remainder will all but disappear in the next
two to three decades. The loss is incalculable. These forests provide habitat for an
estimated half of the world's plant and animal species, provide water and fuel for
much of the world's population, and influence regional and global climate.
Commercial logging, clearance for agriculture, ranching, and fuel gathering are all
responsible for the destruction. Solutions include the development of alternative
fuelwood supplies through fuelwood plantations, the regulation of logging, and a
consensus as to the value of forest conservation over commercial development.
In contrast, temperate-zone forests have actually increased in recent decades.
Their greatest threat is acid rain pollution, which is already severely affecting large
areas of the conifer forests of Europe and northeastern Loss of Agricultural Land.
14. North America
As the world's population increases, the lands needed to produce its food are
disappearing, covered by buildings and roads, their topsoil lost through erosion,
and their productivity destroyed by the salinization caused by irrigation. Large-scale
commercial agriculture in parts of the United States results in severe and
unsustainable rates of erosion soil loss. Overgrazing and firewood gathering denude
vast areas of arid lands, resulting in the inexorable spread of deserts and desertlike
conditions. Much of the problem in the developing countries is caused by unsound
or ineffective development assistance efforts. (See also pollution, land.)
15. Loss of Biological Diversity
The ever increasing loss of plant and animal species represents a major
conservation concern. Habitat loss, especially in tropical forest areas, is the
greatest threat. Overexploitation threatens some species, such as whales and the
rhinoceros. The Convention on Trade in Endangered Species of Flora and Fauna has
worked well to control trade in most species threatened by commercial exploitation.
A more fundamental solution, however, must be the establishment of a global
network of areas that protect and maintain representative samples of the world's
ecosystems. Substantial progress has been made toward this goal, and there are
protected areas—on paper at least—in virtually all nations. To strengthen and
augment protected areas where people are excluded, increasing emphasis is being
placed on sustainable development, or "community conservation" where people
live; the objective here is to bring benefits to the people involved so that they will
assist in biodiversity conservation. This approach represents a major new thrust in
both national and international conservation endeavors, and it is now central to the
conservation efforts of international development institutions such as the World
Bank. From the standpoint of conservation, maintaining species of plants and
animals in botanic gardens, zoos, or gene banks may be a last resort but is no
substitute for maintaining species in their natural habitat.
16. Endangered Water Supplies
Water supplies are threatened virtually worldwide with depletion and pollution.
Globally, the major problem is loss of watershed areas through denudation of
vegetation. The solution must come from better land use and the protection of
critical watershed vegetation, along with water conservation and recycling. (See
also pollution, water; water quality; water resources; water supply.)
17. Exhaustion of Nonrenewable Resources
The primary conservation concern in this area is with fossil fuels, both in terns of
exhaustion of supplies and with global warming caused by the carbon dioxide that
is released when fossil fuels are burned. Solutions include improvements in the
efficiency of fuel combustion and pollution control, as well as more-intensive
explorations for alternatives, particularly from solar energy and other renewable
resources.
18. Conservation: Conservation as a Political and Economic Issue
The benefits of conservation are often long term and therefore accrue to future as
well as to present generations. Many of the benefits (environmental quality, for
example) do not neatly fit in conventional cost-benefit economic calculations. Thus
conservation efforts nearly always run counter to the objectives of short-term
economic gain. For example, a lumber company can usually make a greater shortterm profit from rapid, indiscriminate "mining" of the trees in a forest than it can
from careful, selective logging, followed by replanting to assure a sustained yield.
Fishing provides another example. Technological advances have provided modern
fishing fleets with the means to harvest vast quantities of fish, providing short-term
profit but severely depleting fish stocks worldwide.
In developed countries, conservation issues are often clear-cut economic ones.
From the start, the concept of public-trust management of U.S. public lands has
provided a major focus for conflict between conservationists and the economic
interests of loggers, ranchers, and miners, who virtually without cessation have
sought control over the resources of public lands and continue to receive subsidized
access to timber, minerals, and grazing privileges. Short-term economic interests
often conflict with conservation interests where proposed development will create
environmental damage. (An extreme example, but one that is fundamental to
conservation issues, is where development threatens a species with extinction.) The
benefits of development can be quantified; the costs of the anticipated damage
often cannot. Because of the potency of economic motivations, however, the use of
economic incentives to promote conservation represents another new thrust in
conservation.
Recreational use of public lands has increased dramatically, and while this has
created a larger constituency for public-trust management, it has also caused new
problems. Increased numbers of hikers, cyclists, horseback riders, and campers are
overusing many fragile park and wilderness areas, and future access probably must
be limited. Off-road vehicles pose the greatest immediate problem because of their
impact on wild-country ecosystems.
Other conflicts arise over quality-of-life issues, particularly those involving lowversus high-density commercial and residential additions to towns and suburban
areas. With increasing population pressure, controlling growth has become a highprofile issue in much of the United States. Conservation issues can also have a
potent political dimension, especially where they engender conflicts with those
whose ideology favors "free enterprise" over government involvement.
In developing countries it has become clear that conservation and sound
development are mutually interdependent. Without development, conservation has
little chance of being sustained. Where people live at subsistence level and rely on
burning wood for heat and cooking, they must cut the rapidly diminishing trees
even though they may know that the trees are needed to hold soil and moisture.
Yet development that does not take environmental factors into account also has
little chance of continuance. For example, unless the watershed above a new dam is
protected, its trees may be cut down and the resultant erosion will silt up the dam,
making it useless. The interdependence of conservation and development is well
illustrated by those development projects which ignored environmental concerns
and caused massive deforestation in Latin America, desertification in Africa, and
salinization in Asia. Famines in Africa have been exacerbated, if not substantially
caused, by development projects that did not incorporate environmental
considerations.
Conservation can maintain the resource base needed by developing countries, and
it can contribute directly to economic development, as in Kenya and Costa Rica,
where wildlife-based tourism earns a significant percentage of those nations'
foreign currency. Increasingly, conservation concerns are being incorporated into
economic development plans. At the U.N.-sponsored 1992 Earth Summit in Rio de
Janeiro, the largest congregation of world leaders in history agreed on the broad
principles that must guide environmental policies while still encouraging economic
growth. Binding treaties commit most of the Earth's nations to curb the emission of
greenhouse gases and to protect endangered species.
19. Global Warming: Introduction to Global Warming
The term global warming is used by the general public to refer to the phenomenon
of global change arising from human activities that result in an increase in
greenhouse gases, notably carbon dioxide, in the atmosphere. One manifestation of
this climate change is the observed rise in global mean temperature at the Earth's
surface. This climate change involves much more than just increases in global
temperatures, however. Changes in precipitation, drought, and water resources, for
instance, are also involved. Such factors can have a profound impact on the
environment and human endeavors.
Estimates have been made of changes in the Northern Hemisphere's average
surface temperature for the past 1,000 years. This record was constructed using
data from tree rings, corals, ice cores, and historical records for the first 900 years
of this period. Also used were data from instruments, including thermometers and
satellite sensors, for the past 100 years. Significant fluctuations occur in mean
temperature from year to year and from decade to decade. The variations before
1900 are almost completely natural; that is, human activities had little or nothing
to do with them. Such variations arise from changes in the Sun and the effects of
volcanic eruptions. Interactions among the components of the climate system—the
atmosphere, the oceans, the land surface, and sea and land ice—also cause such
variations.
Notably, however, relatively rapid temperature increases started in about 1900. The
rate and duration of this warming are greater than at any other time during the
past 1,000 years. The decade of the 1990s was the warmest of the last millennium;
the early years of the 21st century were even warmer. Human activities, mainly the
burning of fossil fuels, almost certainly played a significant role in causing this
warming. It has been estimated that the influence of human activities exceeded the
bounds of natural variability from about 1980. The rapid warming over the past 100
years is demonstrated by a variety of other independent observations. These
include the melting of glaciers around the world; rising sea level; reduced areal
coverage of Arctic sea ice; warming of the surface, and of the upper layers, of the
ocean; decreases in Northern Hemisphere snow cover; thawing of the Arctic
permafrost; and shortening of the length of the freezing season in the Northern
Hemisphere.
As indicated by recent reports of the Intergovernmental Panel on Climate Change
(IPCC), by far the majority of credible atmospheric scientists around the world
agree that the observed global warming over the past 100 years is real. The IPCC is
an international body of scientists convened by the United Nations (UN) jointly
under the UN Environmental Programme and the World Meteorological
Organization. Initiated in 1988, the IPCC was charged with providing policy makers
with an objective assessment of the scientific basis for global climate change and its
environmental and socioeconomic aspects. It was to focus particularly on assessing
the effects of human activities. The IPCC's 2001 report stated that global warming
is real. It declared that "there is new and stronger evidence that most of the
warming observed over the past 50 years is attributable to human activities."
It is hard to overemphasize the importance of global warming on the scale shown
during the past 100 years. In particular, the recent changes are occurring at an
unprecedented rate. They exceed anything seen in the past 10,000 years.
Ecosystems are extremely sensitive to climate and evolve rather slowly as climate
changes. When the changes are rapid, many ecosystems are stressed. Some
cannot adapt. If the recent global warming continues or accelerates during the next
50 to 100 years, as is projected by most scenarios, the Earth will experience a
climate hotter than any in the past million years. The consequences will affect all
life, including humans, in ways that are highly uncertain but potentially disastrous.
As the oceanographer Roger Revelle pointed out in 1957, humankind is engaging in
an enormous geophysical experiment whose outcome is in doubt. The doubt comes
from uncertainties as to how human activities will change and how the complex
climate system, which is affected by human activities as well as by natural
processes, will respond.
The attribution of global warming to human activities is controversial because the
Earth's climate system is complicated. It is therefore difficult to determine cause
and effect with certainty. It is also controversial because proposals to mitigate the
causes—such as reducing fossil-fuel burning and other forms of consumption—pose
threats to some industries and some parts of the economy. Nevertheless, the
continuing changes over the past several years have led almost all skeptics to
agree that humans are causing global warming. Skeptics now tend to argue more
about how much temperature increase is due to humans and whether it could also
have some beneficial effects.
20. Global Warming: Factors That Cause Climate Change
Long before the existence of humans, or before their numbers were large enough to
affect weather and climate, climate changed. Many factors combine to produce
climate variation on all scales of time and space. These range from the age of the
Earth itself (4.5 billion years) to individual seasons and months and from local cities
and regions to the size of the entire globe. Fundamental to determining climate and
climate change is the radiation balance of the Earth. This balance indicates how
much solar radiation is received; how much and where this solar radiation is
absorbed by the Earth system (atmosphere, oceans, and land and ice surfaces);
how much and where the components of the Earth system emit infrared radiation
back into space; and how the atmosphere and oceans respond to these heating and
cooling distributions and their variations in time.
Factors that determine the radiation balance of the Earth system and the circulation
of the atmosphere and oceans are listed here and discussed below: (1) the Earth's
orbital parameters; (2) the solar output and its variations; (3) changes in the
surface of the Earth (including continental drift, mountain building and decay, and
changes in ocean basins and sea-bottom topography); and (4) changes in
atmospheric composition (including volcanic gases and particulates, greenhouse
gases, and aerosols and particulates).
21. Solar Variability and Earth's Orbit
The Sun is by far the primary source of energy for the Earth. The variations in total
energy output from the Sun are very small. They amount to about plus or minus
0.1% over the 11-year solar cycle. The direct heating effect of this magnitude of
change is too small to explain the major fluctuations that have been reported; it is
estimated, however, that warming by perhaps as much as 0.2 C degrees (0.36 F
degrees) in the first part of the 20th century may have been due to changes in the
Sun. Even though the variation in the total energy output from the Sun is small, the
variation in the ultraviolet wavelengths is much larger (about 1% to 10%). This
magnitude is enough to affect the amount of stratospheric ozone (see ozone layer),
which is a strong absorber of solar radiation in the stratosphere. Changes in the
stratospheric heating due to changes in ozone modify stratospheric circulation;
moreover, through coupling with the troposphere and the oceans, they also modify
the weather and climate near the Earth's surface. These positive feedbacks may
amplify the direct effects of small variations in solar radiation. Paleoclimatology
records over thousands of years have indeed shown a strong correlation of climate
with solar variability. It is therefore likely that the Sun has contributed to events
such as the Little Ice Age (from A.D. c.1300 to c.1850). Nevertheless, the details of
the connection between solar variability and climate change are far from resolved.
A definite and well-understood factor in changing climate is the slow variation in the
Earth's orbit around the Sun. This factor causes significant changes in seasonal and
latitudinal distribution of solar energy. These changes—which occur in cycles of
about 21,000, 45,000, and 100,000 years—drive the huge variation in the climate
associated with glacial and interglacial periods.
22. Changes in the Earth's Surface
The response of the climate to solar radiation depends strongly on the
characteristics of the surface of the Earth, whether involving water, snow, bare
ground, or vegetation. This is because the different surfaces absorb and reflect the
sunlight and infrared radiation received from the atmosphere in very different ways.
The two principal factors that determine what happens to the radiation received at
the surface are albedo (reflectivity) and moisture availability. Surfaces with high
albedo, such as snow, reflect as much as 90% of the solar radiation back into
space. Dark surfaces, such as water or dense forests, reflect as little as 5% of the
solar radiation. What happens to the radiation that is absorbed depends greatly on
the effective moisture availability. Over moist surfaces, most of the energy goes
into evaporation and moistens rather than heats the lower atmosphere. Over dry
surfaces such as deserts, most of the energy goes into heating the atmosphere.
Therefore, changing the surface of the Earth through activities such as
deforestation or irrigation can cause significant differences in the local, regional,
and perhaps global climate.
On very long time scales (millions of years), major geographic features of the Earth
have varied. These variations—including the locations of the poles, the drift of
continents, and the building and decay of mountains—have profound effects on the
Earth's radiation balance. They also greatly affect the general circulation of the
atmosphere, including important features of climate such as monsoons. For
example, the Himalayas are quite effective in preventing the mixing of warm and
cold air masses to their south and north.
23. Atmospheric Changes: The Greenhouse Effect
The greenhouse effect is a popular term for the effect that certain variable
constituents of the Earth's lower atmosphere have on surface temperatures. These
trace gases—water vapor, carbon dioxide (CO2), methane, nitrous oxide,
chlorofluorocarbons (CFCs), halocarbons, and others—keep ground temperatures at
a global average of approximately 14° C (58° F). Without them, the average would
be about −19° C (−2° F), and the oceans would be frozen. Greenhouse gases have
this heating effect because infrared radiation emitted by the Earth's surface is
absorbed, or trapped, by the gases and radiated both out into space and back
toward the surface. (The effect was originally thought comparable to the way in
which a greenhouse stays warm, hence the term. The main reason that the inside
of a greenhouse is warmer than the outside is not radiative effects, however; it is
the prevention of mixing of cold outside air with warm inside air.) An example of a
runaway greenhouse effect is Earth's near-twin planetary neighbor, Venus. Because
of Venus's thick CO2 atmosphere, the planet's cloud-covered surface is hot enough
to melt lead.
People are concerned that increases in greenhouse gases—particularly increases
caused by human activities—could cause the Earth's surface to warm up to a
dangerous level. Even a small rise in average surface temperature might lead to at
least partial melting of the polar ice caps and hence a major rise in sea level. Sea
level has already risen by about 15 cm (6 in) in the past 100 years. Other adverse
environmental effects might include the destruction of ecosystems and wider
weather and climate extremes.
Water vapor is the most important greenhouse gas, contributing to roughly 60% of
the total greenhouse effect. It is the main reason why humid regions experience
less cooling at night than do dry regions. CO2 is the second most important,
contributing another 26%. Variations in the atmosphere's CO2 content played a
major role in past climatic changes. Since the beginning of the Industrial Revolution
(about 1750), atmospheric CO2 has increased by approximately 31%, largely as the
result of the burning of fossil fuels. This buildup comes about because carbon
dioxide persists for a very long time, estimated at more than a century; further
emissions hence lead to greater CO2 atmospheric concentration. Nitrous oxide,
methane, and CFCs are also long-lived. If the many other determinants of the
Earth's present global climate remain more or less constant, the CO2 increase will
raise the average temperature at the Earth's surface. With the warming of the
atmosphere, the amount of water vapor would probably also increase, because
warm air can contain more water than cooler air. This cycle of warming caused by
increased CO2, which causes more water vapor, which in turn causes further
warming is an example of a positive feedback in the climate system. A negative
feedback, and the most important "brake" on the system, is that the long-wave
(infrared) radiation emitted by the Earth system increases rapidly as its
temperature rises.
Carbon dioxide is emitted not only by human activities but also by natural
processes such as forest fires and decaying vegetation. It is also removed from the
atmosphere by growing vegetation and absorption in the oceans. A great deal
remains unknown about this cycling of carbon through the environment. In
particular, little is known about the role of oceans in the atmospheric carbon cycle.
24. Atmospheric Changes: Aerosols
Aerosols, tiny airborne particulates in the atmosphere, affect the climate in two
different ways. Depending on their type, they can either absorb or reflect solar
radiation. They thereby either cool or warm the atmosphere. Aerosols can also have
an indirect influence on temperature through their effect on clouds and
precipitation. Some aerosols act as nuclei upon which cloud drops form. They can
therefore affect the number and size of water drops in clouds, which affects the
albedo and the precipitation efficiency. For example, a large number of aerosols can
cause clouds to contain many very small drops that are too light to fall out as
precipitation. Thus through the indirect effect, aerosols cause brighter clouds that
are less efficient in producing precipitation.
Aerosols occur naturally when winds blow up dust from dry land areas or when
volcanoes erupt and inject aerosols into the upper troposphere or lower
stratosphere. Aerosols were injected into the stratosphere during the eruption of
Mount Pinatubo in the Philippines in 1991; these aerosols reflected enough radiation
back into space to cool the surface by up to 5 C degrees (9 F degrees) for two years
following the eruption.
Humans are now adding huge amounts of aerosols to the atmosphere, exceeding
natural sources (except volcanoes). Satellite photos show massive clouds of
aerosols blowing off the continents of Asia, North America, and South America. The
net effect of these aerosols is a cooling off of the lower atmosphere, partially
offsetting the warming effect of increasing greenhouse gases, and a reduction in
rainfall. Aerosols emitted from the surface are washed out of the atmosphere by
precipitation, however; they typically last only about a week. Therefore, unlike the
greenhouse gases, they do not build up in the atmosphere. Their effects are
primarily regional. This difference between aerosols and the behavior of the longlived greenhouse gases complicates projections of future climate changes.
25. Natural Variability, Feedbacks, and Abrupt Climate Change
The many factors that cause the climate to change are all responsible to some
degree for causing the fluctuations of the past. Even if every one of the external
factors were constant (for example, the orbital parameters of the Earth), however,
the climate would still vary over many time scales. This is because the atmosphereocean-land system is highly nonlinear and interactive on many time and space
scales. The individual internal properties of the climate system oscillate from one
state to another. Through feedbacks, they affect other properties in complex ways.
One example is the El Niño–La Niña cycle; this involves a strong coupling between
the ocean and the atmosphere in the equatorial Pacific. During an El Niño,
equatorial Pacific Ocean temperatures are as much as 5 C degrees (9 F degrees)
above normal. The easterly trade winds weaken and are replaced by westerlies, and
the sea-level pressure patterns over the Pacific and many other parts of the world
are modified. These variations are accompanied by significant changes in the
atmospheric circulation patterns, jet streams, and storm tracks, with associated
shifts in cold and warm anomalies and precipitation patterns. These shifts have an
enormous impact on agriculture and fisheries in some parts of the world, notably
North and South America, Australia, Indonesia, and parts of Africa and southern
Asia.
Because of the complex nonlinear interactions among the components of the
climate system, the climate may not always change gradually. Abrupt changes
(major transformations that occur within only a few years) are possible that are
difficult to predict. An example of a possible abrupt climate change could be
associated with a shutdown of the global ocean circulation. Called the thermohaline
circulation, this is driven by differences in density associated with temperature and
salinity. The thermohaline circulation is a giant conveyor belt of water that
transports heat and salt around the world; it plays a key role in determining the
climate. In the thermohaline circulation of the North Atlantic, warm, relatively light
surface water in the Gulf Stream flows to high latitudes; there it cools and becomes
saltier, because evaporation exceeds precipitation. The denser water sinks and
returns southward in the deep ocean. The thermohaline circulation is relatively
sensitive, so that small fluctuations in climate could cause considerable changes in
the circulation or even shut it down completely. For example, melting of Arctic ice
and increased precipitation over North America might freshen the surface water of
the North Atlantic portion of the conveyor belt, thereby reducing its density; this
would prevent the sinking branch of the circulation, causing the whole circulation to
slow down or stop. The consequences for the climate in northern Europe would be
severe.
26. Global Warming: Estimates of Impacts of Global Warming
The Sun is by far the primary source of energy for the Earth. The variations in total
energy output from the Sun are very small. They amount to about plus or minus
0.1% over the 11-year solar cycle. The direct heating effect of this magnitude of
change is too small to explain the major fluctuations that have been reported; it is
estimated, however, that warming by perhaps as much as 0.2 C degrees (0.36 F
degrees) in the first part of the 20th century may have been due to changes in the
Sun. Even though the variation in the total energy output from the Sun is small, the
variation in the ultraviolet wavelengths is much larger (about 1% to 10%). This
magnitude is enough to affect the amount of stratospheric ozone (see ozone layer),
which is a strong absorber of solar radiation in the stratosphere. Changes in the
stratospheric heating due to changes in ozone modify stratospheric circulation;
moreover, through coupling with the troposphere and the oceans, they also modify
the weather and climate near the Earth's surface. These positive feedbacks may
amplify the direct effects of small variations in solar radiation. Paleoclimatology
records over thousands of years have indeed shown a strong correlation of climate
with solar variability. It is therefore likely that the Sun has contributed to events
such as the Little Ice Age (from A.D. c.1300 to c.1850). Nevertheless, the details of
the connection between solar variability and climate change are far from resolved.
A definite and well-understood factor in changing climate is the slow variation in the
Earth's orbit around the Sun. This factor causes significant changes in seasonal and
latitudinal distribution of solar energy. These changes—which occur in cycles of
about 21,000, 45,000, and 100,000 years—drive the huge variation in the climate
associated with glacial and interglacial periods.