Global warming (2009) TỪ VỰNG HAY THEO TOPIC

Global warming also called climate change refers to rising global temperatures caused by high levels of carbon dioxide and other so-called greenhouse gases in the atmosphere.. In the fil

Global Warming

by Debra A Miller

Global Warming

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Lucent Books

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ISBN-13: 978-1-4205-0049-3 ISBN-10: 1-4205-0049-X

Miller, Debra A.

Global warming / by Debra A Miller.

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ISBN 978-1-4205-0049-3 (hardcover)

1 Global warming I Title.

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the radio, they are inundated with a nearly continuous stream of data from electronic media They send and receive e-mails and instant messages, read and write online “blogs,” participate in chat rooms and forums, and surf the Web for hours This trend

is likely to continue As Patricia Senn Breivik, the former dean

of university libraries at Wayne State University in Detroit, has stated, “Information overload will only increase in the future By

2020, for example, the available body of information is expected

to double every 73 days! How will these students find the formation they need in this coming tidal wave of information?”

in-Ironically, this overabundance of information can actually impede efforts to understand complex issues Whether the topic

is abortion, the death penalty, gay rights, or obesity, the deluge

of fact and opinion that floods the print and electronic media is overwhelming The news media report the results of polls and studies that contradict one another Cable news shows, talk ra-dio programs, and newspaper editorials promote narrow view-points and omit facts that challenge their own political biases

The World Wide Web is an electronic minefield where mate scholars compete with the postings of ordinary citizens who may or may not be well-informed or capable of reasoned argument At times, strongly worded testimonials and opinion pieces both in print and electronic media are presented as fac-tual accounts

legiti-Conflicting quotes and statistics can confuse even the most diligent researchers A good example of this is the question of whether or not the death penalty deters crime For instance, one study found that murders decreased by nearly one-third when the death penalty was reinstated in New York in 1995 Death

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F oreword 5

penalty supporters cite this finding to support their argument that the existence of the death penalty deters criminals from committing murder However, another study found that states without the death penalty have murder rates below the national average This study is cited by opponents of capital punishment, who reject the claim that the death penalty deters murder Stu-dents need context and clear, informed discussion if they are to think critically and make informed decisions

The Hot Topics series is designed to help young people wade through the glut of fact, opinion, and rhetoric so that they can think critically about controversial issues Only by reading and thinking critically will they be able to formulate a viewpoint that

is not simply the parroted views of others Each volume of the series focuses on one of today’s most pressing social issues and provides a balanced overview of the topic Carefully crafted nar-rative, fully documented primary and secondary source quotes, informative sidebars, and study questions all provide excellent starting points for research and discussion Full-color photo-graphs and charts enhance all volumes in the series With its many useful features, the Hot Topics series is a valuable resource for young people struggling to understand the pressing issues of the modern era

Global warming (also called climate change) refers to rising

global temperatures caused by high levels of carbon dioxide and other so-called greenhouse gases in the atmosphere At least some of these greenhouse gasses are produced by burning fossil fuels such as oil, natural gas, and coal In recent years, global warming has become the world’s most urgent environmental is-sue Many commentators attribute the rising public awareness about this issue to the efforts of former American vice president and 2000 presidential candidate Al Gore, who since his defeat in the presidential race has waged a worldwide publicity campaign about the dangers of global warming Gore’s campaign began with speeches and a slide show of compelling photos, graphs, and time lines, but in 2006, Gore unveiled a documentary and

book on the topic, both named An Inconvenient Truth

The documentary was critically acclaimed and won two

2006 Academy Awards for best documentary and best original song In the film, Gore uses humor, science, and personal sto-ries to show how human activities that produce carbon dioxide and other greenhouse gases are the cause of the rise in Earth’s temperatures Warmer temperatures, Gore warns, are melting the polar ice caps and leading to dramatic climate changes such

as rising sea levels that could engulf some of the world’s major coastal cities The film claims global warming may already be producing frightening weather, including stronger hurricanes, flooding, and torrential rains for some parts of the world, and record heat and drought in other areas These climate changes,

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Gore says, could in turn result in numerous other problems—

everything from new mosquito-borne disease pandemics to the loss of animal species, such as the polar bear, that cannot adapt quickly enough to the rapid temperature increases

Later in 2006, Gore won an international award—the Nobel Peace Prize—for his efforts He shared the award with scientists from the Intergovernmental Panel on Climate Change (IPCC),

a United Nations (UN) organization set up to investigate and report on the causes, effects, and solutions to climate change In his acceptance speech in Oslo, Norway, on December 10, 2007, Gore said, “We, the human species, are confronting a plane-tary emergency, a threat to the survival of our civilization that

is gathering ominous and destructive potential.” He urged the public and policy makers to act now to prevent what could be-come catastrophic disasters in the future, explaining, “We have the ability to solve this crisis and avoid the worst, though not all,

of its consequences, if we act boldly, decisively and quickly.”1

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Former vice president Al Gore (center) receives the Nobel Peace Price for his work

on climate change on December 10, 2007.

G lobal w arminG : a P lanetary e merGency

The other recipient of the Nobel Prize, the IPCC, was ored because of a series of scientific reports it has issued over the past two decades, which the Nobel committee said had cre-ated a broad consensus about the connection between human activities and global warming The IPCC’s latest report, “Climate Change 2007: Mitigation of Climate Change,” warned that un-less governments act quickly to reduce global emissions, green-house gases could rise by 25 to 90 percent over year 2000 levels

hon-by the year 2030 The report urged governments to slow and reverse these emissions trends and stabilize the level of green-house gases remaining in the atmosphere at around 445–490

At the U.S embassy in Hamburg, Germany, environmental activists from the group Greenpeace voice their disapproval of the Bush administration’s nonsupport of the Kyoto Protocol in 2001.

parts per million (ppm)—a level that would hold average global temperature increases to 3.6 to 4.3 degrees Fahrenheit (2 to 2.4 degrees Celsius) This IPCC goal, however, would require gov-ernments to reduce emissions dramatically over today’s levels

In fact, experts say countries such as the United States would need to reduce emissions by at least 80 percent by 2050, and Gore urges the country to take the lead with a 90 percent reduc-tion in the United States

Such significant emissions reductions, however, will be a daunting challenge given the United States’ history of virtually ignoring global warming President George W Bush, for ex-ample, began his administration by abruptly reversing a cam-paign promise to regulate U.S carbon dioxide emissions and

by withdrawing the United States from ongoing negotiations on the Kyoto Protocol, an international treaty negotiated in 1997 that set targets for emissions reductions by developed nations

Instead, Bush advocated an approach based on what he called

“greenhouse gas intensity,” a way of measuring greenhouse emissions according to economic output Under this approach, companies are urged to produce more products while generat-ing the same or fewer greenhouse emissions Critics say this plan masks the true levels of U.S greenhouse gas emissions, because

it allows the administration to report reductions in “greenhouse gas intensity” when in reality the United States is increasing its total emissions year after year The Bush administration also op-posed the Climate Stewardship and Innovation Act of 2005—a bill introduced by Senators John McCain and Joe Lieberman to limit the total greenhouse gases emitted by U.S electricity gen-eration, transportation, industrial, and commercial sectors to the amounts emitted in 2000 And the Bush administration resisted efforts to treat carbon dioxide as a pollutant under the federal Clean Air Act and to strengthen vehicle mileage standards Fi-nally, administration representatives in 2007 blocked progress

on negotiating a global treaty with mandatory caps on sions, instead pushing for separate talks to discuss voluntary emission cutbacks Elections in November 2008 will produce

emis-a new Americemis-an president, but until then no one knows whemis-at future course the U.S government will take

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G lobal w arminG : a P lanetary e merGency

Addressing global warming, therefore, will require not only public awareness, but also tremendous political will Yet accord-ing to many commentators and experts, the effort is both nec-essary and worthwhile because it will give humankind a great cause—quite literally, a chance to save the world As Al Gore

argued in a 2007 New York Times article:

The future of all human civilization is hanging in the balance The climate crisis offers us the chance to ex-perience what few generations in history have had the privilege of experiencing: a generational mission; a com-pelling moral purpose; a shared cause; and the thrill of being forced by circumstances to put aside the pettiness and conflict of politics and to embrace a genuine moral and spiritual challenge.2

Since the planet was first formed, Earth’s climate has

con-stantly changed and evolved, and temperatures have varied widely Throughout the period of human civilization, however, the world has been enjoying a warm, temperate, and relatively stable climate This stability has allowed human civilizations, along with countless other species of animals and plants, to pro-liferate and flourish in recent centuries The release of carbon and other gases from the burning of fossil fuels in the last hun-dred years, however, may be causing a dramatic spike in global temperatures Scientists have been studying this phenomenon since the 1950s, but only recently has a consensus emerged—

that Earth is getting warmer due to human activities

Natural Climate Changes

Climate scientists have known since the eighteenth century that Earth’s climate can change dramatically due to natural causes

In fact, evidence from ice cores extracted from the Arctic and Antarctic regions show that planetary temperatures have varied

by more than 20 degrees Fahrenheit (11.2 degrees Celsius) ing the last 350,000 years Long periods of lower temperatures have resulted in prolonged ice ages that lasted tens of thousands

dur-of years Approximately every 100,000 years, these cold phases have been interspersed with warmer but shorter interglacial pe-riods More than 18,000 years ago during the last ice age, called

the Pleistocene Ice Age, massive glaciers up to eight thousand

feet thick covered almost a third of the Earth’s land surface, cluding much of North America, Europe, and Asia Areas not covered by glaciers were largely cold and desolate deserts that supported only very hardy plant and animal life

in-Within these larger climate fluctuations, smaller-scale ing and cooling cycles have historically occurred Many of these climate changes have been abrupt, and they appear to have caused mass extinctions of large numbers of the planet’s animal and plant species The end of the dinosaur era, for example, coincided with

warm-a sudden globwarm-al cooling thwarm-at mwarm-ay hwarm-ave been cwarm-aused by warm-a lwarm-arge warm-teroid colliding with the Earth Since before the dawn of human

as-These Pleistocene-era human footprints may have been preserved for more than 18,000 years at the height of the last ice age During this time period, massive glaciers covered almost a third of the Earth’s land surface

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civilization, however, the Earth has been experiencing an cial period of unprecedented stability, with no major climate fluc-tuations Cold deserts and glaciers have given way to lush forests, grasslands, and an abundance of plant and animal species, and the human population has soared under these conditions

intergla-Yet today’s relatively stable global climate is fueled by a ber of climate forces—such as volcano activity, cloud cover, the changing intensity of the sun’s radiation, and varying ocean cur-rents and temperatures—that have caused fluctuations in tem-peratures during the last thousand years During the Medieval Warm Period, for example, which lasted from approximately

num-a.d 1000 to 1350, temperatures were warm and comfortable for humans From around 1400 to about 1860, however, the Earth experienced what has been called the Little Ice Age—a small drop of about 0.9 degree Fahrenheit (0.5 degree Celsius) that produced harsh winters, shorter growing seasons, and a drier climate Yet even this slightly colder period caused crop failures and other problems, including a potato famine in Ireland that reduced the Irish population by about 25 percent in just six years between 1845 and 1851

The Greenhouse effect

Scientists say that the Earth’s temperatures are largely determined

by the balance between the amount of sun energy entering the atmosphere and the amount of energy lost from the Earth into space One of the most important climate mechanisms affecting this balance is a natural greenhouse effect—a band of gases that trap the heat emanating from the planet’s surface similar to the way a glass greenhouse warms the air inside its glass walls during

a cold winter These gases include water vapor, methane, nitrous oxide, chlorofluorocarbons, and tropospheric ozone, but the single most important greenhouse gas is carbon dioxide, which accounts for the largest part of the greenhouse effect

These greenhouse gases allow visible sunlight energy to etrate deep into the atmosphere, where much of it is absorbed by the oceans and land masses When this stored energy is released back toward space as infrared radiation, or heat, the greenhouse gases then act as an insulating blanket, absorbing and holding the

pen-heat in the lower atmosphere and helping to maintain the warm temperatures needed for humans to survive As climate expert Mayer Hillman explains, “Without this natural greenhouse effect, the planet would be over 35º cooler than it is now—too cold for

us to inhabit.”3

The amount of heat trapped in this greenhouse process, ever, varies depending on a number of factors Some sunlight never reaches the Earth’s surface because it is reflected back into space by clouds and various types of particles and pollutants in the air In addition, different regions on the planet’s surface re-flect and absorb solar radiation differently The ice caps at each

how-of the Earth’s poles, for example, act as giant mirrors that reflect back most of the sunlight that hits them, while exposed desert soils, oceans, and forested areas tend to absorb more of the sun’s energy, helping to heat the atmosphere A third factor is the con-centration of greenhouse gases in the atmosphere, with higher levels producing more warming All these elements must be in balance to produce average global temperatures that are in the relatively narrow range necessary for humans, plants, and ani-mals to survive on the planet’s fragile surface, seas, and skies

As British scientist and environmentalist James Lovelock has

re-This diagram shows the “greenhouse effect.” Sunlight enters the atmosphere and heats the Earth; the heat is then reflected back into the atmosphere, but greenhouse gases cause some of the heat to be trapped from the planet’s surface

sunlight enters atmosphere, heating the Earth

heat is reflected back into the atmosphere

greenhouse gases cause some of the heat to be trapped carbon dioxide

and oth er

ga

se s

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minded us, the portion of the Earth that supports life is only “a thin spherical shell of land and water between the incandescent interior of the Earth and the upper atmosphere surrounding it.”4

The warming effects of the Industrial revolution

Until recently, humans did not significantly affect the much larger forces of climate and atmosphere Many scientists believe, how-ever, that with the dawn of the industrial age—and the burning

of fossil fuels such as coal, natural gas, and oil—humans began

to significantly add to the amounts of carbon dioxide and other greenhouse gases in the atmosphere, enhancing the planet’s nat-ural greenhouse effect and causing higher temperatures

The Industrial Revolution began in the late eighteenth and early nineteenth centuries in Great Britain when manual labor began to be replaced by machinery fueled by new sources of energy The first sign of this change was mechanization of Eng-land’s textile mills, the development of iron-making techniques, and the increasing use of coal rather than wood and water power for heating, industry, and transportation Around 1850, steam power was invented as a way to use coal energy more efficiently, and soon steam engines were used to power trains, ships, and in-dustrial machinery of all sorts These inventions spread through-out Europe, the United States, and other regions, bringing enor-mous changes in society and commerce Later in the nineteenth century, scientists learned how to generate electricity, and the discovery of oil led to the invention of the internal combustion

climate chanGe threatenS Society

“Climate change is the single greatest threat that societies face today.” —James Gustave Speth, environmentalist and dean of the Yale School of Forestry and Environmental Studies.

James Gustave Speth, “The Single Greatest Threat: The United States and Global

Climate Disruption,” Harvard International Review, Summer 2005 http://hir.harvard.

edu/articles/1346/.

engine, both technological developments that further changed the way humans lived and worked around the globe

By the end of the twentieth century, the world was completely dependent on and rapidly depleting the planet’s fossil fuels—

resources such as coal, natural gas, and oil that are formed from the decomposed remains of prehistoric plants and animals As Hillman explains, “Fossil fuels contain the energy stored from the sun that took hundreds of thousands of years to accumulate, yet within the space of a few generations—a mere blink of the planet’s life so far—we are burning it.”5

The result of this rapid burning of fossil resources, many entists believe, is rising concentrations of greenhouse gases that may be overheating the planet Scientists have determined, for ex-ample, that concentrations of carbon dioxide have been increasing

sci-Around 1850, steam power was invented as a way to use coal energy more ficiently, bringing enormous changes in society and commerce Here, a worker operates a steam engine in 1854.

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since the beginning of the Industrial Revolution In 1750, there were 280 ppm of carbon dioxide in the atmosphere, but by 2005, the levels of carbon dioxide had risen to 380 ppm, an increase of over one-third And much of this increase has occurred in recent years, since 1959, as world energy usage has expanded dramati-cally The United States is responsible for almost a quarter of the world’s greenhouse gas emissions, and China is the second-largest emitter Other countries with high emissions include members of the European Union, while the lowest emissions come from vari-ous nations in Africa

The major source of human-produced greenhouse emissions—

accounting for approximately 65 percent—is the use of fossil els to power industry, transportation, home heating, electricity generation, and cooking However, carbon emissions are also increased when carbon-absorbing forests are cut down to make way for human developments and woodlands, grasslands, and prairies are converted into farmland for agriculture As geog-raphy professor Michael Pidwirny explains, “Rural ecosystems can hold 20 to 100 times more carbon dioxide per unit area than agricultural systems.”6 Together, these human activities are believed to account for at least 28 percent of the Earth’s total greenhouse emissions, with the balance produced by natural sources

fu-The scientific study of Global warming

Scientists have long suspected a link between industrialization and global warming, but serious study of the issue did not begin until the second half of the twentieth century In 1896, Swedish scientist Svante Arrhenius was the first to suggest that the burn-ing of fossil fuels adds carbon dioxide gas to the Earth’s atmo-sphere and could raise the planet’s average temperature At the time and for decades thereafter, however, Arrhenius’s discovery

of the greenhouse effect was dismissed by the mainstream entific community, which reasoned that such a major climate change would not likely be produced by humans and could only happen slowly over tens of thousands of years Most scientists at the time also believed that the vast oceans would absorb most of the carbon dioxide produced by industry

sci-By the 1950s and 1960s, however, improved instruments for measuring long-wave radiation allowed scientists to prove that Arrhenius’s theory was correct At that time, studies also confirmed that carbon dioxide levels were indeed rising year af-ter year In 1958, Charles D Keeling, a scientist with the Scripps Institute of Oceanography in California, conducted the first reli-able measurements of atmospheric carbon dioxide at Hawaii’s Mauna Loa Observatory and found concentrations of the gas to

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Global warming skeptics criticize former vice president Al Gore for exaggerating scientific assessments and predictions and presenting an alarmist portrayal of global warming In a March 13, 2007, article in

the New York Times, for example, columnist

William J Broad cited several scientists who criticized Gore’s portrayal of global warm- ing as a terrible catastrophe that will cause soaring temperatures, seas that

might rise twenty feet, and more frequent and more deadly hur- ricanes According to scientists quoted in the article, tempera- tures are the highest in four hun- dred years, but no higher than they were sixteen hundred years ago during the Medieval Warm Period The article also says most scientists agree that warmer tem- peratures will likely make many storms and hurricanes stronger, but notes that the latest Atlantic hurricane season produced fewer hurricanes than predicted (five instead of nine), none of which hit the United States Similarly, although seas are expected to rise, most experts think this will be a very slow process—

according to the Intergovernmental Panel

on Climate Change (IPCC), up to three feet by the end of the century Other scientists, however, defend Gore and think that he is presenting the big picture of cli- mate change accurately.

twenty-William J Broad, “From a Rapt Audience, a Call to

Cool the Hype,” New York Times, March 13, 2007

Criticisms of Al Gore’s Claims

Al Gore has been criticized for his portrayal of global warming.

Over the next several decades, scientists used a variety of methods to study exactly how the Earth’s temperature was changing Some scientists studied ancient tree rings, corals, fos-sils, pollens, sediment cores, ice cores, and cave stalactites—

called paleoclimatic data—to compare ancient temperatures with modern data This paleoclimatic record allowed research-ers to examine global temperature fluctuations over the last sev-eral centuries and even farther back in time Still other research-ers devised mathematical models of the climate, which allowed for predictions to be made about temperature changes when the amount of carbon dioxide input was increased In recent decades, these climate models have been greatly improved by the use of computers, which can incorporate massive amounts

of weather information into the climate formulas and produce much more accurate predictions of future climate changes Also during the last twenty years, scientists began to use satellites to observe the Earth’s changing climate All of the methods of glob-

al warming study have some scientific uncertainties, but each suggested that the Earth has warmed over the last hundred years and that it is likely to grow even warmer due to rising levels of carbon dioxide and other greenhouse gases

scientific Uncertainty

Despite these scientific findings, however, there was considerable disagreement within the scientific community about global warm-ing throughout the 1980s and 1990s Many scientists accepted that a warming trend was likely but believed that average tempera-tures would rise only a few degrees in the next century—not a sig-nificant change that seemed to require immediate policy changes

In addition, a number of scientists were equally concerned about the effects of smog—air pollutants from fossil fuels that could po-tentially block sunlight and cause the world to cool, rather than heat up In fact, a cooling trend was recorded between the 1940s and 1970s, when air pollution became a serious problem in devel-oped countries such as the United States No one was completely sure whether the Earth would dip into another ice age or heat up

as global warming theory predicted Most scientists at this time

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agreed only that the Earth’s climate was very complicated and that more research was needed before accurate predictions about the effect of human activity on climate change could be made

In the 1980s, largely because of antipollution efforts made by the United States and other industrialized nations, air pollution began to decrease and average global temperatures again began

to rise More research followed, including the collection of sive amounts of weather data by oceangoing ships and Earth-orbiting satellites, and consultation among scientists around the globe As information about the climate increased, a growing number of scientists became more convinced of the existence and potentially serious impacts of global warming, and they be-gan to warn policy makers of the need to address the problem

mas-The IPCC

Scientists’ efforts to draw attention to climate change were aided

in the summer of 1988, when temperatures around the globe soared to the highest levels on record, helping to focus public attention on the issue That same year, the rising concerns about global warming prompted the world’s governments to organize the Intergovernmental Panel on Climate Change (IPCC), an in-dependent panel of world climate scientists Created as part of the UN, the IPCC was asked to examine the available scientific, technical, and socioeconomic evidence on human-induced cli-mate change and provide advice to the international community about its impact and possible solutions

climate chanGe may be natural

“The Earth was evidently coming out of a relatively cold period

in the 1800s so that warming in the past century may be part

of this natural recovery.” —John R Christy, climate and spheric science expert at the University of Alabama.

atmo-Testimony of John R Christy to the Committee on Environmental and Public Works, Department of Atmospheric Science and Earth System Science Laboratory, University of Alabama in Huntsville, July 10, 1997.

In 1990, the IPCC published its First Assessment Report

The report concluded that increased greenhouse gas emissions caused by human activity “will enhance the greenhouse effect, resulting on average in an additional warming of the Earth’s surface.”7 The 1990 report served as a scientific and technical basis for negotiating a UN agreement on global warming called the UN Framework Convention on Climate Change, adopted in

1992, in which nations pledged to try to stabilize greenhouse gas emissions

Several scientists from the Intergovernmental Panel on Climate Change (IPCC) answer questions on global warming during a press conference in 2001 During this session, chairman Dr Robert Watson and other scientists warned that global warming will cause an increase in air pollution and other disasters, including droughts.

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A Second Assessment Report was issued by the IPCC in

1995 At this time, the IPCC again concluded that the increase

in global temperatures was likely caused, at least in part, by man activities However, the report cautioned that it had “not been possible to firmly establish a clear connection between regional [climate] changes and human activities”8 because of in-adequate data about weather variability over the twentieth cen-tury Nevertheless, the IPCC recommended that nations act to reduce emissions, and the report provided information that led

hu-to the 1997 adoption of the Kyohu-to Prohu-tocol—an international treaty that set binding targets for the reduction of greenhouse emissions by developed countries

In 2001, in its Third Assessment Report, the IPCC announced that the majority of the world’s scientists believed the Earth was facing significant global warming due to greenhouse gas emis-sions released by the burning of fossil fuels The report also said that “there is new and stronger evidence that most of the warm-ing observed over the last 50 years is attributable to human activ-ities.”9 The IPCC predicted that temperatures would most likely rise about 3.8 degrees Fahrenheit (2 degrees Celsius) by 2100, and that this would cause significant climate changes and risks

to ecosystems This assessment helped to convince many people that climate change is a serious environmental, social, and politi-cal problem Yet the report conceded that there were still some scientific uncertainties about the causes and impacts of global warming that required additional study

“A broad array of scientists said the latest [IPCC] analysis was the most sobering view yet of a century of transition—after thou- sands of years of relatively stable climate conditions—to a new norm of continual change.” —Elisabeth Rosenthal and Andrew

C Revkin, reporters for the New York Times.

Elisabeth Rosenthal and Andrew C Revkin, “Panel Issues Bleak Report on Climate

Change,” New York Times, February 2, 2007

Six years later, in 2007, the IPCC released a Fourth Assessment Report that made its strongest case yet about the dangers of global warming This time, the IPCC concluded that global warming is “un-equivocal,” and that the world’s rising temperatures are “very likely”10

(defined as 90 percent certainty) to be the result of human ties such as the burning of fossil fuels The report confirms that the atmospheric levels of carbon dioxide and methane, two important greenhouse gases, are higher than they have been for 650,000 years

activi-Since the dawn of the industrial era, the report found, concentrations

of both gases have increased at a rate unprecedented in more than 10,000 years The result, the IPCC concluded, is rapid warming with significant temperature increases expected in the future

A scientific Consensus

According to most commentators and scientists, the IPCC ports establish that there is a scientific consensus that climate change is occurring and that it is the result of human activities

re-In 2004, Naomi Oreskes, a science professor at the University of California at San Diego, surveyed 928 abstracts of peer-reviewed papers related to global climate change and found that none of them disagreed with the IPCC position In a widely discussed

article published in the journal Science, Oreskes stated,

“Scien-tists publishing in the peer-reviewed literature agree with IPCC, the National Academy of Sciences, and the public statements

of their professional societies [that global warming is caused by human activities].”11

“The greenhouse effect must play some role But those who are absolutely certain that the rise in temperatures is due solely to carbon dioxide have no scientific justification It’s pure guess- work.” —Henrik Svensmark, director for Sun-Climate Research

at the Danish National Space Center.

Quoted in Copenhagen Post, “Cosmic Rays Linked to Global Warming,” October 4,

2006.

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Today, most scientists continue to support the conclusions

of the IPCC In a joint statement issued in 2007 (after the IPCC’s Fourth Assessment Report was released), science academies in the major industrialized countries—including Canada, France, Germany, Italy, Japan, Russia, the United Kingdom, and the United States—as well as a number of developing nations, stat-ed: “It is unequivocal that the climate is changing, and it is very likely that this is predominantly caused by the increasing human interference with the atmosphere These changes will transform the environmental conditions on Earth unless counter-measures are taken.”12

Members of the IPCC attend the IPCC XXVII opening session ceremony on November 12, 2007 Most scientists support the conclusions of the IPCC that climate changes are occurring due to human activities.

Global warming skeptics

Despite the apparent convergence of scientific opinion on the causes and dangers of global warming, a few skeptics remain

Most skeptics agree that global temperatures are increasing, but they believe that temperature fluctuations are relatively small and primarily caused by natural forces

One area of disagreement, for example, revolves around a perature graph used by global warming advocates called the “hock-

tem-ey stick” (because it is shaped like a hocktem-ey stick) This graph, ally attributed to University of Massachusetts geoscientist Michael Mann, shows that there have been virtually no global temperature variations over the past thousand years in the Northern Hemi-sphere, except during the last hundred years, when temperatures have sharply peaked, presumably due to humans’ use of fossil fuels

usu-Some critics of this graph cite errors in the Mann analysis, and others charge that it conveniently omits natural temperature fluctuations

Some scientists emphasize the

contribu-tion of natural climate change to today’s

warming temperatures A study of

cli-mate published in the magazine Nature on

February 10, 2005, for example, showed a

significant temperature swing between the

twelfth and twentieth centuries and a

cool-ing period that ended around 1800 The

study, conducted by scientists at Stockholm

University, also showed that temperatures

in the twentieth century were similar to

those in the eleventh and twelfth centuries,

but temperatures in the last fifteen years

appear to be warmer than during any

pre-vious time These results appear to track

a thousand-year-long climate simulation undertaken by another research group that included two natural forces—solar radia- tion and volcanic dust—believed to affect global temperatures Experts say these studies suggest that the Earth’s climate

is naturally variable and that changes in the sun’s radiation and volcanic eruptions may be the cause However, the increased warming during the past fifteen years still supports the idea that humans, too, are contributing to global warming.

Science Daily, “Natural Climate Change May Be Larger than

Commonly Thought,” February 17, 2005 www.science daily.com/releases/2005/02/050212195414.htm.

Natural Climate Change

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such as the Medieval Warm Period and the Little Ice Age Since the Medieval Warm Period produced temperatures much warmer than those the Earth is experiencing today, critics argue that the Earth today may simply be experiencing a similar natural warming cycle following the end of the Little Ice Age

In addition, skeptics question the accuracy of another important piece of evidence relied upon by global warming advocates—climate models, many of which predict the pos-sibility of skyrocketing heat before the end of this century In

Vaclav Klaus, president of the Czech Republic, is an outspoken skeptic of the global warming theory and does not believe that global warming results from human activities.

truth, some critics say, global temperatures may be turning out to be milder than these models predicted Climate scien-tist John Christy, for example, coauthored a 2006 report that found that global temperatures increased only about 0.22 de-gree Fahrenheit (0.12 degree Celsius) per decade since 1958 and only about 0.29 degree Fahrenheit (0.16 degree Celsius) per decade since 1979—far less than most climate models predicted Christy concludes that the Earth is not heating up rapidly and that “the rate of change is rather modest.”13

Skeptics also note that while parts of the planet are warming, such as much of the Northern Hemisphere and the Arctic, the Southern Hemisphere and Antarctica are not experiencing any statistically significant warming In fact, researchers agree that although the Antarctic Peninsula—a sliver of land that projects into the ocean toward the southern tip of South America—is seeing a rapid rise in temperatures that is causing the melting of glacier ice, most of Antarctica has not registered any warming trend in the last fifty years, basically the period for which data is available And some researchers have reported that over the past twenty years, temperatures in Antarctica have actually cooled slightly, accompanied by increasing snowfall and thickening ice

As atmospheric scientist David Bromwich explains, “It’s hard to see a global warming signal from the mainland of Antarctica right now The best we can say right now is that the climate models are somewhat inconsistent with the evidence that we have for the last 50 years from continental Antarctica.”14

These and other criticisms of the global warming science continue to create a seed of doubt among the public and policy makers about whether climate change is truly a threat

In addition to disagreeing about whether global warming is

be-ing fueled primarily by human activities, global warmbe-ing entists and their critics also have differing opinions about exactly how much temperatures will rise In fact, even the forecasts by the IPCC vary depending on a number of factors, primarily how much carbon is released into the atmosphere from human sources Oth-

sci-er climate scientists have proposed that various natural forces may play a role in regulating the Earth’s temperature, potentially affect-ing whether the Earth’s temperatures will cool or warm Most sci-entists and researchers believe the warming trend will definitely continue, but just how warm the planet will get over the next century is still somewhat difficult to predict conclusively

Temperature Changes so Far

Temperatures vary naturally from year to year, but most mate scientists agree that average global temperatures have risen about 1.1 degrees Fahrenheit (0.62 degree Celsius) during the last century, with two-thirds of this warming occurring since the 1970s Temperatures have warmed on land more than in the oceans, and land surface temperature measurements (avail-able since 1860) indicate that the 1990s was the warmest decade ever In fact, according to the IPCC, eleven of the last twelve years were among the twelve hottest years on record

cli-In the United States, the consensus view is that average peratures rose approximately 1 degree Fahrenheit (0.56 degree Celsius) during the last century Most of this warming has oc-curred in the winters, and certain parts of the country such as the coastal Northeast, the upper Midwest, the Southwest, and

tem-Alaska grew much hotter than the 1-degree average According

to past weather data, 1998 was the hottest year in world history, but according to the National Climatic Data Center (NCDC), an organization run by the U.S Department of Commerce that col-lects climate data, 2006 was the warmest year on record for the United States

These conclusions about temperature increases may be what exaggerated, however In 2007, for example, the National Aeronautics and Space Administration (NASA) revised its official

some-Drought and weeks of extreme heat cause thousands of dead fish to line the shore

of Jackson Lake in Franklin, Tennessee, in August 2007 Many climate scientists agree that average global temperatures have risen about 1.1 degrees Fahrenheit (0.62 degree Celsius) during the last century, with two-thirds of this warming oc- curring since the 1970s.

P redictinG the F uture

records of surface temperatures in the United States As global warming critic Joseph Blast of the Heartland Institute explains:

“The revised data show 1998 falling to second place behind 1934

as the warmest year, followed by 1921, 2006, 1931, 1999, and

1953 Four of the top 10 years on record are now from the 1930s while only three of the top 10 (1998, 2006, 1999) are from the past 10 years.”15 Other critics have suggested that worldwide temperatures during the 1990s may have recorded hotter than past decades because hundreds of measuring stations were shut down in cold regions of the world, such as the Soviet Union Also, critics say, many once-rural measuring stations may have been surrounded by urban sprawl—suburban developments with nu-merous roads and concrete parking lots that are known to absorb more sunlight and become much hotter than the countryside

Yet even taking these explanations into account, it is clear to most researchers that the Earth has warmed, particularly in recent decades To the average person the amount of warming so far may seem quite small, but scientists say even minor temperature chang-

es can have significant effects on the climate and ecosystems

Continued warming Predicted

Because greenhouse gases already released into the atmosphere will linger for many years, and because the Earth is slow to adjust

to these changes, the climate is expected to continue to warm

link to human activity GettinG clearer

“Despite all the complexities, a firm and ever-growing body of evidence points to a clear picture: the world is warming, this warming is due to human activity increasing levels of greenhouse gases in the atmosphere, and if emissions continue unabated the warming will too, with increasingly serious consequences.”

—Michael LePage, writer and editor for NewScientist.com, an online science and technology magazine.

Michael LePage, “Climate Change: A Guide for the Perplexed,” NewScientist.com, May

16, 2007 http://environment.newscientist.com/channel/earth/dn11462.

in the future In fact, this continued warming will occur even

if governments act today to reduce emissions from cars, power plants, and other sources As Mayer Hillman explains, “Even if

no additional carbon dioxide were emitted from now on, spheric concentrations would take centuries to decline to pre–

atmo-Industrial Revolution levels.”16

The most widely accepted predictions of future temperature and climate changes are found in the IPCC’s 2007 report Essen-tially, the IPCC says that the degree of global warming will vary depending on the level of future greenhouse emissions So it de-veloped six emission scenarios and, using sophisticated climate simulation programs, projected “best estimate” and “likely range”

future temperatures for each scenario Overall, the IPCC projected

a range of temperature increases between 2 to 11.5 degrees enheit (1.1 to 6.4 degrees Celsius) by the end of the century

Fahr-A boat sits on the dry reservoir bed of the Entrepenas reservoir in Spain in 2006

The IPCC says future warming is expected to be greatest over land and in the high northern latitudes.

P redictinG the F uture

The most optimistic IPCC scenario, for example, assumes that emissions can be dramatically lowered as a result of a rapid change toward a service and information economy and a quick shift toward clean energy technologies Under these conditions, the IPCC predicts a likely range of 0.5 to 1.6 degrees Fahrenheit (0.3 to 0.9 degree Celsius), and a best estimate temperature rise

of about 1.1 degrees Fahrenheit (0.62 degree Celsius) by 2100

If no action is taken to reduce emissions, however, the IPCC concludes that there may be twice as much warming over the next two decades as today And the worst-case scenario predicted by the IPCC suggests that the world might see drastically higher tem-peratures over the next century This scenario assumes that there will be rapid economic growth and continued reliance on fossil-intensive energy production and consumption, and thus continu-ing high levels of greenhouse emissions If this occurs, the IPCC says the world would likely see temperatures soaring somewhere

in the range of 4.3 to 11.5 degrees Fahrenheit (2.4 to 6.4 degrees

According to researchers at the National Oceanic and Atmospheric Administration (NOAA), a U.S government science agen-

cy, the tropics are rapidly expanding due

to global warming In an article published December 13, 2007, in the magazine

Nature Geoscience, the NOAA researchers

found that the tropical zone—a

geograph-ic band around the Earth’s equator—was spreading both northward and southward toward the poles In addition, the study found that this expansion was happening

at a rate much faster than predicted by climate models Under the most extreme

scenario predicted by climate models, the tropical zone was supposed to expand

by about 2 degrees latitude (about 120 miles, or 200 kilometers) by the end of the twenty-first century, but NOAA found this worst-case scenario has already hap- pened The tropical zone includes Florida and parts of the U.S Southwest, as well

as southern Australia, southern Africa, and parts of the European Mediterranean region Experts said this study suggested that these heavily populated areas may face even drier conditions than expected from future global warming.

The expanding Tropics

Celsius), with a best estimate that temperatures would increase by 7.2 degrees Fahrenheit (4 degrees Celsius) by 2100

The IPCC says future warming is expected to be greatest over land and in the high northern latitudes and lowest over the Southern Ocean (also known as the Antarctic Ocean) and parts of the North Atlantic Ocean This means warming will be close to the global average in some regions of the world, such as south Asia, Australia, New Zealand, and southern South Amer-ica However, regions farther north are expected to experience higher than average heat; this includes most of North America, all of Africa, Europe, northern and central Asia, and most of Central and South America

In the United States, according to the IPCC report, tures in northern states will warm primarily in the winters, while southwestern states will experience higher summer temperatures and much less rain IPCC climate models suggest that by 2100 the eastern, western, and southern edges of the country might warm between 3.6 and 5.4 degrees Fahrenheit (2 and 3 degrees Celsius), and the northern regions by 12.6 degrees Fahrenheit (7 degrees Celsius) Alaska may experience the most warming—

tempera-as much tempera-as 18 degrees Fahrenheit (10 degrees Celsius) perature increases in these ranges will almost certainly produce major climate and lifestyle changes for Americans

Tem-Climate Feedbacks

The Earth’s climate is highly complex, however, and experts say

it is possible that the climate could change even more rapidly

warminG iS better than FreezinG

“We’ll continue to get a slow, sunny, erratic warming through the next few centuries—which is far better than the alternative of another harsh, cloudy, unstable Little Ice Age.” —Dennis T Avery, senior fellow at the Heartland Institute, an organization that pro- motes free market solutions to social and economic problems.

Dennis T Avery, “Our Moderate Climate Crisis,” Heartland Perspectives, October 18, 2007.

than scientists now predict One factor that cannot be figured into the climate models used by IPCC scientists is known as climate feedbacks—changes in climate that occur in response

to rising temperatures These feedbacks can either increase or decrease the effects of global warming

One example of positive feedback that could produce ditional warming involves melting Arctic sea ice This melting could, in turn, add to the Earth’s warming because the loss of large sections of highly reflective ice would mean that less sunlight

ad-is reflected back into space and more of thad-is energy ad-is absorbed

by the oceans Similarly, if higher temperatures produce more drought and more forest fires, the decrease in carbon-absorbing greenery and the burning of these organic matters is expected to add carbon to the atmosphere and increase global warming

An even more worrisome positive feedback is the increased rate of decay of organic matter in soils—a process that increas-

es atmospheric carbon levels, enhancing the greenhouse effect

Icebergs are seen melting in Antarctica in 2007 It is unclear whether climate

“feedbacks,” changes in response to warmer temperatures, will increase or decrease the effects of global warming

This phenomenon is expected to be especially widespread in areas in the Arctic region, such as Alaska and Greenland, where higher temperatures could melt permafrost—long-frozen land areas that store massive amounts of carbon from decayed vegeta-tion that grew during prehistoric warm periods Walter Oechel,

a scientist studying this problem, is concerned that this back could tip the Earth into an uncontrollable warming cycle

feed-He explains: “Humans [now] are putting about 6 billion or 7 billion metric tons of carbon in the atmosphere a year, and we are standing on 200 billion tons here [in Alaska] If any signifi-cant portion came out, that dwarfs the current human injection into the atmosphere And once that runaway release occurred, there’d be no way to stop it.”17

Yet another positive feedback that could have a significant effect on temperatures is the release of methane by the world’s oceans and glaciers According to Tessa Hill, a geologist at the University of California at Davis, as oceans warm, oil and gases seep out of the ocean floor, including methane—a greenhouse gas that is considered twenty times more potent than carbon di-oxide at creating global warming Glaciers, too, release a form of methane as they begin to melt, adding to the Earth’s greenhouse effect As Hill explains: “These petroleum seeps appear to be activated by periods of climate change If the Earth is already

in a mode of warming, they ‘turn on’ and become more active, which promotes further warming.”18

iPcc rePort a “ScreaminG Siren”

“The good news is our understanding of the climate system and our impact on it has improved immensely The bad news is that the more we know, the more precarious the future looks

If the last IPCC report was a wake up call, this [2007] one is a screaming siren.” —Stephanie Tunmore, climate and energy cam- paigner for Greenpeace International.

Quoted in Christian Science Monitor, “Key Players React to the IPCC Global Warming

Report,” February 8, 2007 www.csmonitor.com/2007/0208/p25s01-sten.html.

P redictinG the F uture

These positive feedbacks, however, could potentially be set by negative feedbacks An example of a possible negative feedback is the creation of more low clouds from the increased evaporation that will be caused by warmer surface temperatures

off-A greater number of low, thick clouds would tend to cool the climate by reflecting more sunlight back into space and reducing the amount of sun energy that is absorbed by the Earth’s land masses and oceans The absorption of carbon by the oceans is also considered a negative feedback, as is any increased vegeta-tion that might grow in previously cold regions of the Earth due

to warmer temperatures

Meteorologist and prominent global warming critic Richard Lindzen of the Massachusetts Institute of Technology has even suggested that a negative feedback called “infrared iris effect”

could blunt all the positive feedbacks and significantly counter future global warming This theory, first proposed in 2001, sug-gests that global warming may dry out the upper levels of the troposphere, the part of the atmosphere closest to the Earth’s surface, allowing more of the Earth’s heat to escape Lindzen believes this mechanism works something like the iris of the eye: Warmer temperatures produce fewer cirrus clouds (wispy clouds formed from ice crystals), creating holes in cloud for-mations that act to reduce the greenhouse effect naturally As Lindzen explains:

This is a terrifically important feedback because if you double the amount of carbon dioxide in the atmosphere but don’t have any feedback within the system, you only get about 1 degree of warming (averaged over the en-tire globe) But climate models predict a much greater global warming because of the positive feedback of water vapor Yet these models are missing potentially another negative feedback (the infrared iris) which can be any-where between a fraction of a degree and 1 degree—the same order of magnitude as the warming.19

Other scientists have tried to test Lindzen’s theory, with mixed results, leading many to conclude that much more re-search is needed on the role of clouds and precipitation in regu-lating climate

Global dimming

Yet another group of scientists warn that a different cloud phenomenon—“global dimming”—may be masking the true amount of global warming that will occur in the future First studied during the 1990s by Gerry Stanhill, a British scientist, global dimming refers to an increase in air pollution that has been causing a decrease in the amount of sunlight reaching the Earth during recent decades According to Stanhill and other scientists, tiny particles of soot, ash, and other air pollutants—

most of it from the burning of the same fossil fuels that produce greenhouse gases—attract water droplets and then create pol-luted clouds These polluted clouds contain a larger number of droplets than unpolluted clouds, making them more reflective than unpolluted clouds Polluted clouds thus reflect more of the sun’s energy back into space, reducing the amount of sunlight

Airplane contrails criss-cross the sky over Bay St Louis in Mississippi Contrails—the vapor from jets seen as white streaks in the sky—also create sunlight reflection and dimming and polluted clouds.

P redictinG the F uture

reaching the planet’s surface Contrails—the vapor from jets seen

as white streaks in the sky—also create polluted clouds and are another significant cause of sunlight reflection and dimming

Scientists worry that global dimming may be offsetting and hiding the real degree of future global warming—a proposi-tion which, if true, could mean that global warming will soar to much higher levels than currently projected Indeed, if air pollu-tion continues to be reduced, some scientists suggest that aver-age global temperatures may actually rise as much as 18 degrees Fahrenheit (10 degrees Celsius) within the next century Such a staggering temperature increase would destroy many plants and animals that humans depend on for food, medicine, and other products; destroy the world economy; and make many regions

on the Earth uninhabitable for humans

Alternate Theories on Global warming

While some scientists and researchers focus on the ity of a much hotter Earth, another group of scientists believe that global warming may not be as great as currently predicted because natural causes, rather than human activities, account for most of the current rise in temperatures A study published

possibil-in 2005 by scientists from Fpossibil-inland and Germany, for example, identified a strong correlation between solar activity and tem-peratures Specifically, the study found that the sun has been more active in the last 60 years than anytime in the past 1,150 years, and that this increased solar radiation corresponded closely with rising temperatures during the last century Many

“Feedback in our global climate could determine humankind’s future prosperity and even survival.” —Thomas Homer-Dixon, author and professor of peace and conflict studies at the University

of Toronto.

Thomas Homer-Dixon, “A Swiftly Melting Planet,” New York Times, October 4, 2007

www.nytimes.com/2007/10/04/opinion/04homer-dixon.html?_r=1&oref=slogin.