IN A variety of ways, most of us rely on carbon-based fuels. We drive cars and other vehicles powered by gasoline or diesel fuel. We use electricity generated by power plants that consume coal, natural gas, or oil. We burn wood, charcoal, natural gas, and coal to cook or keep warm. All these activities add carbon dioxide to the atmosphere. This gas traps heat from the sun.
We also add other heat-trapping greenhouse gases to the atmosphere. Nitrous oxide is added from nitrogen fertilizers used in agriculture. Methane is emitted by rice paddies and cattle feedlots. Chlorofluorocarbons (CFCs) result from the manufacturing of plastic foams and from other industrial processes. CFCs not only trap heat but also destroy earth’s stratospheric ozone layer.
With the exception of CFCs, which are now regulated, these heat-trapping gases are being emitted into the atmosphere at ever-increasing rates. This is due, in part, to the growing numbers of people on earth, along with the growth of energy use, industrial activity, and agriculture. According to the Washington-based Environmental Protection Agency, humans presently spew six billion tons of carbon dioxide and other greenhouse gases into the atmosphere each year. These greenhouse gases do not simply vanish; they can linger in the atmosphere for decades.
Scientists are generally quite confident about two things. First, in recent decades and centuries, the amount of carbon dioxide and other greenhouse gases in the atmosphere has increased. Second, over the last hundred years, the average surface temperature of the earth has increased between 0.5 and 1.1 degrees Fahrenheit [0.3° and 0.6°C].
The question arises, Is there a connection between global warming and the human-induced buildup of greenhouse gases? Some scientists say probably not, pointing out that the increase in temperature falls within the range of natural variation and that the sun may be responsible. However, many climate experts agree with the wording of a report by the Intergovernmental Panel on Climate Change. It stated that the increase in temperature “is unlikely to be entirely natural in origin” and that “the balance of evidence suggests that there is a discernible human influence on global climate.” Yet, uncertainty remains about whether human activities are warming the planet—especially about how quickly the world may warm in the 21st century and exactly what the consequences might be.
Uncertainties Bring Debate
When climatologists predict a future greenhouse effect, they rely on climate models run on the world’s fastest and most powerful computers. However, the earth’s climate is determined by an extremely complex interaction of the earth’s rotation, atmosphere, oceans, ice, land features, and the sun. With so many factors coming into play on such a vast scale, it is impossible for any computer to predict with certainty what will happen 50 or 100 years from now. Science magazine noted recently: “Many climate experts caution that it is not at all clear yet that human activities have begun to warm the planet—or how bad greenhouse warming will be when it arrives.”
Uncertainties make it easy to deny that there is any threat. Scientists who are skeptical of global warming, along with powerful industries that have an economic interest in maintaining the status quo, argue that the present state of knowledge does not justify what could be costly corrective action. After all, they say, the future may not be as bad as some people think.
Environmentalists counter by saying that scientific uncertainties should not lull policymakers into complacency. While it is true that the future climate may not be as bad as some fear, it is also possible that the situation could be even worse! Moreover, they reason that not knowing for sure what will happen in the future does not mean that nothing should be done to minimize the risk. People who quit smoking, for example, do not first demand scientific proof that if they continue smoking, they will without fail develop lung cancer 30 or 40 years later. They stop because they recognize the risk and want to minimize or eliminate it.
What Is Being Done?
Since there is so much debate about the scale of the problem of global warming—and even as to whether a problem exists at all—it is not surprising that there are differing views on what to do about it. For years environmental groups have promoted widespread use of pollution-free energy sources. Power can be harnessed from the sun, the wind, rivers, and underground reservoirs of steam and hot water.
Environmentalists have also urged governments to pass laws to reduce emissions of heat-trapping gases. Governments have responded on paper. For instance, in 1992, at the Earth Summit in Rio de Janeiro, Brazil, representatives of about 150 countries signed a treaty affirming their commitment to reduce greenhouse-gas emissions, particularly carbon dioxide. The goal was that by the year 2000, greenhouse emissions from industrialized nations would be reduced to 1990 levels. While a few have made progress in this direction, most rich countries are not even close to keeping their modest pledge. Instead of cutting back, most nations are producing more greenhouse gases than ever! In the United States, for example, it is thought that by the year 2000, carbon dioxide emissions are likely to be 11 percent higher than they were in 1990.
More recently, there have been moves to put “teeth” into international agreements. Instead of making cutbacks voluntary as in the 1992 accord, there are calls to set greenhouse emission targets that are mandatory.
The Cost of Change
Political leaders yearn to be viewed as friends of the earth. However, they also keep an eye on the consequences that change may bring to the economy. Since, according to The Economist magazine, 90 percent of the world relies on carbon-based fuel for energy, to move away from using it would bring big changes; and the cost of change is fiercely debated.
What would it cost to reduce greenhouse emissions by the year 2010 to 10 percent below what they were in 1990? The answer to that depends on whom you ask. Consider views in the United States, the country that spews more greenhouse gases into the atmosphere than any other. Industry think tanks warn that such a reduction would cost the U.S. economy billions of dollars every year and put 600,000 people out of work. In contrast, environmentalists say that achieving the same goal could save the economy billions of dollars each year and generate 773,000 new jobs.
Despite calls by environmental groups for immediate action, there are powerful industries—automobile manufacturers, oil companies, and coal producers, to name a few—that use their considerable funds and influence to downplay the threat of global warming and to exaggerate the economic impact of a shift away from the use of fossil fuels.
Debate continues. If, however, humans are altering climate and do nothing about it but talk, the saying that everybody talks about the weather but nobody does anything about it will take on an ominous new meaning.
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The Kyoto Protocol
In December 1997 more than 2,200 delegates from 161 countries met in Kyoto, Japan, to hammer out an agreement, or protocol, to do something about the threat of global warming. After more than a week of discussions, the delegates resolved that developed countries should cut emissions of greenhouse gases to an average of 5.2 percent below 1990 levels by the year 2012. Penalties for violators of the agreement would be determined later. Assuming that all nations adhere to the treaty, how much difference will a 5.2-percent decrease make? Evidently, very little. Time magazine reported: “It would take a 60% reduction to make much of a dent in the greenhouse gases that have been building up in the atmosphere since the start of the industrial revolution.”
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The Greenhouse Effect Illustrated
The Greenhouse Effect: The earth’s atmosphere, like the glass panes in a greenhouse, traps the sun’s heat. Sunlight warms the earth, but the heat that is created—carried by infrared radiation—cannot easily escape the atmosphere. Instead, greenhouse gases block the radiation and send some of it back toward the earth, thus adding to the warmth of the earth’s surface.
2. Trapped infrared radiation
3. Greenhouse gases
4. Escaping radiation
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Forces That Govern Climate
If we are to understand the current debate over global warming, we need to understand some of the awe-inspiring forces that make our climate what it is. Let us consider some basics.
1. The Sun—Source of Heat and Light
Life on earth depends on the immense nuclear furnace we call the sun. Larger than a million earths, the sun provides an ever-reliable supply of heat and light. A decline in the sun’s output would encase our planet in ice; an increase would make the earth a sizzling skillet. Since the earth orbits at a distance of 93 million miles from the sun, it receives only one half of one billionth of the sun’s outgoing energy. Nevertheless, this is just the right amount to produce a climate in which life can flourish.
2. The Atmosphere—Earth’s Warm Blanket
The sun is not alone in determining the temperature of the earth; our atmosphere also plays a critical role. The earth and the moon are the same distance from the sun, so both receive proportionately about the same amount of heat from the sun. Nevertheless, while the average temperature of the earth is 59 degrees Fahrenheit [15°C], the moon averages a chilly zero degrees Fahrenheit [-18°C]. Why the difference? The earth has an atmosphere; the moon does not.
Our atmosphere—earth’s swaddling band of oxygen, nitrogen, and other gases—holds some of the sun’s warmth and lets the rest escape. The process is often compared to a greenhouse. A greenhouse, as you probably know, is a structure with walls and a roof made of glass or plastic. Sunlight enters easily and heats the interior. At the same time, the roof and the walls slow the escape of the heat.
Similarly, our atmosphere allows sunlight to pass through it to warm the earth’s surface. The earth, in turn, sends the heat energy back into the atmosphere as infrared radiation. Much of this radiation does not go straight into space because certain gases in the atmosphere absorb and redirect it back to the earth, adding to the warmth of the earth. This process of warming is called the greenhouse effect. If our atmosphere did not trap the sun’s heat in this way, the earth would be as lifeless as the moon.
3. Water Vapor—The Most Essential Greenhouse Gas
Ninety-nine percent of our atmosphere is made up of two gases: nitrogen and oxygen. Though these gases play a vital role in complex cycles that support life on earth, they play almost no direct role in regulating the climate. The job of climate regulation falls to the remaining 1 percent of the atmosphere, heat-trapping greenhouse gases, which include water vapor, carbon dioxide, nitrous oxide, methane, chlorofluorocarbons, and ozone.
The most crucial greenhouse gas—water vapor—is not usually thought of as a gas at all, since we are used to thinking of water in its liquid form. Yet, each molecule of water vapor in the atmosphere is packed with heat energy. For example, when vapor in a cloud cools and condenses, heat is released, causing powerful convection currents. The dynamic movement of water vapor in our atmosphere plays a critical and complex role in determining both weather and climate.
4. Carbon Dioxide—Essential to Life
The gas talked about most frequently in discussions about global warming is carbon dioxide. It is misleading to condemn carbon dioxide as simply a pollutant. Carbon dioxide is a vital ingredient in photosynthesis, the process by which green plants make food for themselves. Humans and animals breathe in oxygen and breathe out carbon dioxide. Plants take in carbon dioxide and release oxygen. It is, in fact, one of the provisions of the Creator that make life possible on earth.a However, having too much carbon dioxide in the atmosphere would apparently be like throwing an extra blanket on a bed. It could make things warmer.
A Complex Array of Forces
The sun and the atmosphere are not alone in determining climate. Also involved are oceans and ice caps, surface minerals and vegetation, earth’s ecosystems, an array of biogeochemical processes, and the earth’s orbital mechanics. The study of climate involves nearly all earth sciences.
Water vapor (H20)
Carbon dioxide (CO2)
a Almost all life on earth draws energy from organic sources, thus depending directly or indirectly upon sunlight. However, there are organisms that thrive in the darkness on the ocean floor by drawing energy from inorganic chemicals. Rather than photosynthesis, these organisms use a process called chemosynthesis.