How do the activities of humans affect the environment on a continental and worldwide scale?
Human activities have led to continental and even worldwide changes in the environment. The result is called global change, because the changes occur on a huge scale over the entire globe called Earth. Often, the direct causes of these changes are not immediately clear. For example, traces of pesticides can be found in the snow at the North Pole even though humans do not use pesticides anywhere near there. The pesticides somehow traveled thousands of miles through the atmosphere from places where farmers used them to control agricultural pests. In this section you will explore two major examples of global change-acid rain and global warming.
“Whatever befalls the Earth befalls the sons of the earth. Man did not weave the web of life; he is merely a strand in it. Whatever he does to the web, he does to himself. . .”
Chief Seattle, as translated by Dr. Henry Smith
The Earth Speaks
One of the problems created by excessive energy use in North America is acid rain. What is acid rain? How is it formed? How can rain be acidic? What can be done to prevent its formation?
A better name for acid rain is acid precipitation, because snow as well as rain can be acidic. An even better name is acid deposition, because it also includes dry particles that can fall out of the atmosphere and combine with water to form acids.
Rain, in most cases, is naturally acidic. But sometimes it contains impurities that can make it highly acidic. Acidity is the amount of acid in a substance. Measuring the acidity of a liquid is measuring of one property of that liquid. You probably know other measurements of the properties of a liquid, such as its temperature, volume, and weight. Acidity is measured in terms of pH, much like temperature is measured in degrees. Vinegar, lemon juice, and cola are some examples of acidic liquids that you know. The opposite of acidity is alkalinity (al-ka-LIHN-ih-tee). Shampoo and milk are examples of alkaline liquids.
Figure 10.1 The sources of acid rain may be located far from where the acid rain has the most damaging effects.
The most acidic rain ever measured in the mountains of the eastern United States was 2,000 times more acidic than unpolluted rain. That means it was like lemon juice falling from the sky!
Sulfur dioxide and nitrogen oxides are gases in the atmosphere. These gases can mix with water in the atmosphere. When enough of these gases mix with water, they change into sulfuric and nitric acids. The acids mix with water vapor and fall to earth when it rains. Sulfur dioxide is a chemical with molecules that are made up of one atom of sulfur and two atoms of oxygen. Sulfur dioxide is written SO2 in scientific shorthand. Nitrogen oxides are chemicals with molecules made of one atom of nitrogen and one or two molecules of oxygen. Scientific shorthand for nitrogen oxides is NOx. The X indicates either one or two atoms of oxygen.
How would you solve the problems caused by acid rain in the Northeastern United States? Would your solution be fair to the people in the Midwest? Would it be fair to the people in the Northeast? Explain your reasoning.
How do sulfur dioxide and nitrogen oxides get into the atmosphere? Most come from the smokestacks of power plants and factories and the tailpipes of automobiles. SO2 and NOx are released as byproducts when fossil fuels such as gasoline or coal are burned. SO2 and NOx in the air can drift hundreds of miles before falling out of the sky as acid rain. For this reason, many of the places suffering the effects of acid rain are not necessarily near the source of the pollution, as shown in Figure 10.1.
Acid rain affects land organisms and water organisms. The needles of evergreen trees can be damaged by acid rains.
Acid rain tends to acidify the lakes and rivers on which it falls. Many aquatic organisms are affected by the acidity of the water in which they live. Acid rain has caused the decline of fish populations in lakes in the Adirondack Mountains of New York and in the rivers in Nova Scotia. Some insects such as water boatmen can live in lakes with a wide range of acidities. Other organisms such as fresh water mussels are very sensitive to acidity and can live only in fairly neutral waters. The bar graph in Figure 10.2 on page 64 compares how much acidity some different organisms are able to tolerate.
Figure 10.2 Different aquatic organisms can tolerate different amounts of lake acidity. The shaded bars on this graph show the range of acidities in which these organisms can live.
Suppose you found a water boatman, a salamander, and a may fly while you were exploring a stream. What would you guess the pH of the stream would be? If you found only water boatmen in a second stream, would you guess that the second stream has a higher or lower pH than the first? (Hint: Look at Figure 10.2 and make sure that you notice that pH gets lower as you go up the vertical axis.)
Acid rain washes away calcium that normally cycles in forests. When this happens, calcium isn't available in the food chain, and birds can't get the calcium they need to make strong eggshells. As a result, birds living in areas with heavy acid rain are more likely to lay thin, fragile eggs. The fragile eggs break when the birds try to sit on them to keep them warm.
Which of the effects of global warming do you think is more dangerous to humans: sea levels rising or rainfall patterns changing? Why? Should people who are not directly affected by these global warming effects do anything to decrease greenhouse gases? Why or why not?
Limiting the release of sulfur dioxide and nitrogen oxides would reduce the problem of acid rain. This can be done in several ways. For example, using more fuel-efficient automobiles and installing scrubbers that clean smokestack emissions will reduce the release of harmful gases. These changes sound easy but often are not done because they are expensive. Also, the people who suffer the effects of acid rain are often not the ones who cause the problems. Most of the pollution that causes acid rain in the northeastern United States actually comes from big Midwestern cities such as Chicago, Detroit, Cleveland, and Pittsburgh. So people in the Northeast have to convince people in the Midwest to burn their fossil fuels more wisely, even though the Midwest people don't benefit directly. In fact, it may cost them more money!
Another problem you've probably heard about on the news is global warming. You read a little about global warming on page 24. Global warming is the continuing increase of Earth's temperature. If the present trend continues over the next hundred years, the average temperature of the earth's atmosphere may become warmer than it has been for the past million years. Although this change doesn't sound that bad, even a small increase in temperature could lead to some harmful changes. Melting ice caps can increase ocean waters and cause flooding of low-lying areas near the ocean. Global warming can increase the length of the hurricane season. Also, global warming can increase the amount of rain in some areas and decrease the amount of rain in others. Although most places will become warmer, weather patterns may change so that a few could become cooler.
Figure 10.3 Greenhouse gases trap the sun's energy in the Earth's atmosphere.
Many scientists think global warming is likely to happen because humans have added excessive amounts of carbon dioxide to the atmosphere by burning fossil fuels. Gases called CFCs (chlorinated fluorocarbons) found in some air conditioners and refrigerators also are being released into the atmosphere. Carbon dioxide and CFCs are greenhouse gases that have the ability to trap heat in the atmosphere.
Sometimes simple changes can stop the production of substances that can harm the environment. One disk-drive factory in California was the single largest source of CFC-113 emissions in the United States in 1987 because it used CFC-113 to clean circuit boards. Now, the company simply dunks the circuit boards in soapy water and blow-dries them. This is a good example of a corporation seeing a problem and finding a solution to the problem. It's important for other corporations, individuals, and groups of people to do the same type of problem solving.
Remember that greenhouse gases trap heat in the atmosphere. This process of trapping heat is similar to the way that glass keeps the sun's heat trapped in automobiles and greenhouses. Normally, energy from the sun reaches Earth, warms it, and then some bounces back to space. But when greenhouse gases are in the atmosphere, the heat that would normally bounce out into space is trapped and stays to warm the atmosphere. This process, sometimes called the greenhouse effect, is shown in Figure 10.3.
What are some of the possible effects of global warming? One of the most dramatic effects would be the rise in sea levels. Because water takes up more room when it is warmer, the volume of the world's oceans will increase. Scientists predict that sea levels around the world will rise anywhere from 0.2 meters to 2.2 meters. Many low-lying areas near the ocean would be permanently flooded. For example, most of the Florida Keys and the Everglades would be completely underwater!
Another likely effect of global warming would be a change in precipitation patterns. Some places that receive a lot of rain now could dry up, while others that don't get much rain now could be flooded! Currently, scientists predict that the central United States will be much drier. This region is sometimes called the nation's “breadbasket.” But continued global warming could make the area too dry even to grow wheat.
Figure 10.4 Greenhouse gases have increased significantly during the industrial age.
Carbon dioxide is responsible for about 71% of the greenhouse effect. Every year people in the U.S. add at least 1.5 billion tons (1.36 billion metric tons) of carbon dioxide to the atmosphere by burning fossil fuels.
One way to prevent global warming is to reduce the amount of greenhouse gases that human activities put into the atmosphere. This could be done by reducing the amount of fossil fuels burned and, perhaps, replace them with fuels that don't produce carbon dioxide. Scientists are now looking at ways to use hydrogen-based fuels and solar energy to achieve this goal.
Activity 10-1: Feeling the Heat: The Greenhouse Effect
There is evidence that human activities are causing the Earth's average temperature to rise at a slow but steady rate, Scientists have called this phenomenon the greenhouse effect. What exactly is the greenhouse effect? What causes it? What are its consequences? Are there possible solutions?
- Glass bowls or containers of various sizes
- Colored paper
- Activity Report
Step 1 Discuss the following questions, Write your responses on your Activity Report.
- Why do scientists think gases such as CO2 trap heat in the atmosphere?
- Will increased CO2 in the atmosphere cause an increase in global temperature? Explain.
- How is the greenhouse effect expected to influence your life? Human life in general? The environment?
Step 2 Design and create physical models of Earth under two different conditions-without high levels of greenhouse gases and with high levels of greenhouse gases.
- What part(s) of your physical model represents “normal” levels of greenhouse gases? What part(s) represents high levels?
- How does changing your model's “atmosphere” affect other parts of your model, such as air temperature?
- How can you change parts of your model such as temperature to lessen the effects of a rise in greenhouse gases?
Step 3 Discuss the following questions, Write your responses on your Activity Report.
- How closely does your model represent real life?
- In what ways could your model be improved?
Step 4 Use your model to create a presentation to teach the class about the greenhouse effect. Your presentation should include its causes, consequences, and possible solutions. Use the responses on your Activity Report to begin developing your presentation.
- What causes acid rain?
- Does acid rain affect only the people who live near its source?
- What is global warming?