For over 100 years, scientists have known about the physical mechanism that causes the Earth to warm. Today, they call it the "greenhouse effect." Generally, it works like this:
- Radiation from the Sun in short wavelengths easily passes through the Earth's atmosphere and strikes the surface, which reflects much of it back as longer wavelengths.
- Instead of going back into space, the longer wavelengths are absorbed by gases in the atmosphere.
- The atmosphere reflects back to the Earth's surface a significant amount of the trapped radiation, which becomes heat.
Thus, the Earth warms much like a greenhouse or automobile does when the Sun's rays penetrate the glass, but are trapped inside as heat.
Water vapor and other gases in the atmosphere capture and return to Earth about 50 percent of the Sun's incoming radiation. The warming that results is necessary to prevent our planet from becoming extremely cold and hostile to life. But over the past few centuries, human activities on Earth have increased the concentration of some gases in the atmosphere that intensify heating. These gases include carbon dioxide (CO2), methane, nitrous oxide, and others, the so-called "greenhouse gases."
The Evidence of Climate Change
In 1896, a Swedish chemist, Svante A. Arrhenius, became the first scientist to hypothesize that burning fossil fuels (mainly coal, oil, and natural gas) releases CO2 into the atmosphere, which leads to a warming of the Earth's surface. Later, scientists discovered that the rise of CO2 and other greenhouse gas concentrations seemed to begin with the Industrial Revolution and speeded up in the 20th century.
To be sure, there are a number of ways that the Earth can become warmer naturally. Periods of global warming in the past were caused by changes in the Earth's orbit, volcanic eruptions, and variations in the Sun's radiation output. But natural causes apparently cannot explain the current warming of the Earth.
In 1988, the United Nations established the Intergovernmental Panel on Climate Change (IPCC). The purpose of the IPCC is to review the work of scientists around the world to assess the evidence of climate change.
In 2001, the IPCC issued its third report, assessing the evidence of climate change. The IPCC found that during the 20th century, the Earth warmed by about 1degree Fahrenheit. One degree does not seem like a lot. But scientists know that at various times in Earth's history, shifts of just a few degrees had a dramatic impact on the planet's climate and environment. Here are some other major 20th century climate changes that the IPCC reported:
- While some areas of the world experienced worsening droughts, others had greater rainfall and flooding.
- Most of the world's glaciers were melting.
- The average sea level rose several inches.
- Plant and animal habitats are moving.
The IPCC also found that the concentration of CO2 in the atmosphere rose by about 30 percent during the last 200 years, the period of the Industrial Revolution. CO2 is the most important greenhouse gas that traps heat from the Sun.
In addition, the IPCC discovered "new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities." About 75 percent of CO2 emissions come from burning fossil fuels. Americans produce more than their share of these emissions and are responsible for 35 percent of all greenhouse gases ever produced by humans.
Most of the remaining CO2 emissions result from the destruction of forests. Since 1855, humans have destroyed up to 20 percent of the world's rain forests in places like Brazil. Burning forests to clear land for farming, roads, and settlement injects large amounts of CO2 into the atmosphere.
Trees take in CO2 in order to grow. They convert CO2 to oxygen as part of their metabolic process. With fewer trees, less CO2 is converted. The destruction of trees hinders nature's way of removing this greenhouse gas from the atmosphere. Scientists refer to forests, farmlands, and the oceans as "carbon sinks," because they remove CO2 from the atmosphere. The problem is that widespread deforestation is decreasing a major sink.
The Persistent Minority
A persistent minority of the world's scientists disagree with the findings of the IPCC. In his book, Hot Talk, Cold Science: Global Warming's Unfinished Debate, environmental science scholar S. Fred Singer points out that there are many things scientists do not yet know. For example, they are not sure how muchCO2 is absorbed by the ocean carbon sink.
Rather than assuming an environmental disaster will result from global warming, Singer identifies its potential benefits. He foresees more food from longer growing seasons, an increase in timber, more water in some dry regions, and a decrease in the use of fossil fuels for heating as winters become more moderate.
Perhaps the greatest uncertainly identified by scientists like Singer involves clouds. As the Earth warms, these scientists predict, ocean evaporation will increase, causing more high cirrus clouds to form. A greater global cloud cover will reflect more of the Sun's radiation back into space and actually cool the planet.
What If We Do Nothing?
Humans have changed the environment since prehistoric times. But environmental disasters in the past were limited to local regions. Today, human activities on a worldwide scale appear to be changing the global climate. Moreover, most scientists now agree that, on balance, global warming is likely to have a negative impact on the planet.
What is likely to happen over the next 100 years if we do nothing about global warming? The IPCC's third assessment report includes the best available projections of likely impacts on the world's environment.
According to the IPCC's report,CO2 concentrations in the atmosphere will double by 2100. This will cause an average increase in the global surface temperature between 3.5F and 10F. The rate of temperature increase during the century will very likely be greater than at any time in the last 10,000 years.
Increasing temperatures will mean more droughts in many areas of the world, including parts of the United States such as the Southwest. In these areas, crop yields will decline and more forest fires will occur. The decreased food supply in poor countries experiencing drought will often lead to famine.
Insects will thrive in a warming world. Many insect-borne diseases like malaria will expand into new regions where the people have little natural resistance.
While some parts of the world will suffer from heat and dryness, other regions will experience increased rainfall along with floods, landslides, and soil erosion. Violent storms will threaten human life, health, and property, driving up insurance rates.
Throughout the 21st century, glacier and icecap melting will accelerate in the Northern Hemisphere. It is possible that the entire Greenland ice cap could melt away, adding to the projected three-foot rise in sea level by 2100.
The rising seas will cause major flooding and loss of land in the coastal regions in the world, affecting tens of millions of people. Low-lying small Pacific islands will likely disappear beneath the waves. A side effect of the warming seas may be the shifting of ocean currents, which could have a major influence on weather over landmasses and commercial fishing.
Ecosystems unable to cope with the climate changes will be at risk. Up to 50 percent of the world's wetlands may be lost before the end of the century. While some animal, bird, and fish species will successfully expand their ranges, those unable to adapt will become extinct. The good news for humans is that even through the worst of the global warming Homo sapiens will survive.
A recent study by a large insurance company estimated the economic impact of global warming if CO2 concentrations double in the 21st century. The study concluded that weather damage, crop losses, and other expenses will cost the world $300 billion per year.
Poor countries in Africa, Asia, and Latin America, which have historically introduced the least amount of greenhouse gases into the atmosphere, will suffer the greatest economic hardships. But when the Earth's surface temperature increases more than a few degrees, even industrialized countries like the United States will experience economic hardships.
There will be some positive benefits from global warming, such as longer crop growing periods. But these benefits will probably not be enough to overcome significant damage to the environment.
What Should We Do About Global Warming?
In 1992, the United States and the other industrialized nations agreed to reduce their greenhouse gas emissions to 1990 levels. This agreement, however, was not legally binding.
In 1997, more than 160 nations met at Kyoto, Japan, to work out a treaty requiring reductions of greenhouse gas emissions. A proposed exemption of all economically developing countries from any mandatory limits on their emissions proved to be a major obstacle. These countries argued that such limits would severely weaken their economic development.
Despite opposition from the United States and other industrialized nations, the developing countries exemption was included in the final treaty. The industrialized countries agreed to reduce their greenhouse gas emissions up to 8 percent below 1990 levels by 2015. This should stabilize the greenhouse effect and begin to slow damage to the global environment.
The Kyoto Treaty included no specific methods that nations had to use to reduce their emissions. Nations would probably have to consider options such as limiting deforestation, requiring more fuel-efficient automobiles, or imposing a "carbon tax" on gasoline and other fossil fuels to discourage usage. Relying more on solar, wind, and nuclear power would also reduce greenhouse gas emissions.
President Bill Clinton signed the Kyoto Treaty, but the U.S. Senate refused to ratify it because of the developing countries' exemption and possible threats to the American economy. In 2001, President George W. Bush withdrew the United States from the Kyoto Treaty. He argued that its percentage requirements for greenhouse gas reductions would cost Americans millions of jobs. A few months later, 180 nations met without the United States to implement the treaty.
In 2002, President Bush came up with his own plan for reducing U.S. greenhouse gas emissions. He proposed a mix of alternative fuel research and tax credits to encourage companies to reduce their emissions voluntarily over a 10-year period. This approach, Bush said, would cut greenhouse gas emissions to levels comparable to those required by the Kyoto Treaty without damaging the American economy.
Critics of President Bush's plan faulted his heavy reliance on voluntary action by companies and claimed that U.S. emissions would grow substantially. Sen. John Kerry (D-Mass.) argued that Congress should set higher fuel-efficiency standards for cars and SUVs. President Bush opposed this because it may force manufacturers to make these vehicles smaller and more expensive.
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Global warming is real. The debate centers on what to do about it. The dilemma is how to reduce greenhouse gas emissions without damaging the world economy.
For Discussion and Writing
- Make a list of five impacts on the world's environment that are likely to occur in the 21st century if we do nothing about global warming. Rank these changes from most to least important from your point of view. Give reasons for the single most important change on your list.
- Do you think developing countries should be exempted from mandatory reduction of greenhouse gas emissions? Explain.
- What is the basic difference between the Kyoto Treaty approach and that of President Bush in reducing greenhouse gas emissions?
For Further Information
Intergovernmental Panel on Climate Change Established by the United Nations and World Meteorological Organization.
Global Warming Links A large collection of links. All the starred (recommended) sites are critics of global warming. From JunkScience.com.
Global Warming News stories from World News.
Global Climate Change Student Information Guide An online book by Joe Buchdahl, Manchester Metropolitan University.
The 200-Year Story of Global Warming by Gale E. Greenhouse Christianson.
You Can Prevent Global Warming (and Save Money!): 51 Easy Ways by Jeffrey Langholz and Kelly Turner.
Red Sky at Morning: America and the Crisis of the Global Environment by James Gustave Speth.
Limits to Growth: The 30-Year Update by Donella H., Jorgen Randers, Dennis L. Meadows.
The Carbon War: Global Warming and the End of the Oil Era by Jeremy K. Leggett.
Taken By Storm: The Troubled Science, Policy and Politics of Global Warming by Christopher Essex, Ross McKitrick.
Dead Heat: Globilization and Global Warming by Tom Athanasiou and Paul Baer.
High Tide: The Truth About Our Climate Crisis by Mark Lynas.
Hot Talk, Cold Science: Global Warming's Unfinished Debate by S. Fred Singer.
Global Warming: The Hard Science by L. D. Danny Harvey.
The Global Warming Debate by John Emsley.
Global Warming Links Enormous collection of links.
Global Change and Climate Change Links From Institute for Technology Assessment and Systems Analysis.
A C T I V I T Y
The Global Warming Summit
In this activity, students take part in a mock Global Warming Summit meeting.
1. Form four role groups to represent the viewpoint of the following sets of countries at a Global Warming Summit meeting:
A. Small poor countries already experiencing drought, flooding, or rising sea levels.
B. Large developing countries like China, India, and Brazil that are trying to speed up their economic development.
C. European and other industrialized countries, except the United States.
D. United States
2. The first task for each set of nations will be to prepare a statement on its viewpoint about global warming and the Kyoto Treaty. Each should then report its viewpoint to the other nations.
3. The next task will be for each set of nations to prepare and argue for specific strategies to address the global warming problem. Refer to the article for ideas, which may include voluntary actions by nations and individuals as well as national and international laws.
4. The last task will be for the participants to attempt to write a legally binding international treaty on global warming that all four sets of nations are willing to sign.
"Alaskan Glaciers Melting Faster Than Once Thought." Los Angeles Times. 19 July 2002:A19. • Christianson, Gale E. Greenhouse, The 200-Year Story of Global Warming. New York: Penguin Books, 1999. • "Chronology—The Fight Against Global Warming." Reuters. 28 Oct. 2001. • Cortese, Amy. "As the Earth Warms, Will Companies Pay?" New York Times. 18 Aug. 2002:6. • Foroohar, Rana and Guterl, Fred. "Will We Ever Stop Global Warming?" Newsweek International. 17 June 2002. • "Global Warming." UN Chronicle. No. 2, 1997. • Harrack, Nicholas M. "Bush Proposes Kyoto Alternative." United Press International. 14 Feb. 2002. • Hinrichsen, Don. "The Oceans Are Coming Ashore." World Watch. Nov./Dec. 2002. • "IPCC Third Assessment Report—Climate Change 2001: Impacts, Adaptation, and Vulnerability, Summary for Policymakers." Intergovernmental Panel on Climate Change. 13-16 Feb. 2001. • "IPCC Third Assessment Report—Climate Change 2001: The Scientific Basis, Summary for Policymakers." Intergovernmental Panel on Climate Change. Jan. 2001. • "IPCC Third Assessment Report—Climate Change 2001: Synthesis Report, Summary for Policymakers." Intergovernmental Panel for Climate Change. 24-29 Sept. 2001. • Kelly, Robert. The Carbon Conundrum, Global Warming and Energy Policy in the Third Millennium. Houston, Tex.: CountryWatch, 2002. • Kerry, John. "Bush Takes a Backseat." Time. 26 Aug. 2002:A49. • MacDonald, Alexander E. "The Wild Card in the Climate Change Debate." Issues in Science and Technology. Summer 2001. • McFarling, Usha Lee. "Study Links Warming to Epidemics." Los Angeles Times. 21 June 2002:A7. • Sarewitz, Daniel and Pielke, Roger. "Breaking the Global-Warming Gridlock." Atlantic Monthly. July 2000. • Shogren, Elizabeth. "U.N. Issues Grim Pre-Summit Report on Environment." Los Angeles Times. 14 Aug. 2002. • Spotts, Peter N. "Global Climate Treaty Moves Ahead Without US." Christian Science Monitor. 24 July 2001. • U.S. Department of State. U.S. Climate Action Report 2002. May 2002. U.S. Environmental Protection Agency. • Whitman, Christine Todd. "A Strong Climate Plan." Time. 26 Aug. 2002: A48.