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Copyright Pearson Prentice Hall

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Biology


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6-4 Charting a Course for the Future


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Ozone Depletion

What are two types of global change of concern to biologists?


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Researchers are gathering data to monitor and evaluate the effects of human activities on important systems in the biosphere. Two of these systems are:

• the ozone layer high in the atmosphere

• the global climate system


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Ozone Depletion

Ozone Depletion

Between 20 and 50 kilometers above Earth's surface, the atmosphere contains a relatively high concentration of ozone gas. This layer of the atmosphere is called the ozone layer.

The ozone layer absorbs a good deal of harmful ultraviolet, or UV, radiation from sunlight before it reaches Earth's surface.


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Ozone Depletion

Exposure to UV can:

• cause cancer

• damage eyes

• decrease organisms' resistance to disease

• damage plant leaf tissue and phytoplankton in the oceans


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Ozone Depletion

Early Evidence

In the 1970s, scientists discovered a hole in the ozone layer over Antarctica.

After it was first discovered, the ozone hole grew larger.


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Ozone Depletion

A similar ozone hole also appeared over the Arctic.

In 1974, a research team published data showing that gases called chlorofluorocarbons, or CFCs, could damage the ozone layer.


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Ozone Depletion

One Solution

CFCs were once widely used:

• as propellants in aerosol cans

• as coolant in refrigerators, freezers, and air conditioners

• in the production of plastic foams

The U.S. and other nations began reducing the use of CFCs in 1987, and eventually banned them.


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Ozone Depletion

Since the ban, the level of CFCs in the atmosphere has decreased, indicating that the ban will have positive, long-term effects on the global environment.

Current data predict that the ozone holes should shrink and disappear within 50 years.


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Global Climate Change


All life on Earth depends on climate conditions such as temperature and rainfall.

Many ecologists are concerned about strong evidence that climate is changing.


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Since the late 19th century, average temperatures have risen about 0.6 Celsius degrees.

Data indicate that since 1980, average temperatures have risen between 0.2 and 0.3 Celsius degrees.


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The term used to describe the increase in the average temperature of the biosphere is global warming.

One sign of global warming is melting polar ice.


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Evidence of Global Warming

The geological record shows that Earth’s climate has changed repeatedly during its history.

Researchers must determine whether the current warming trend is part of a larger, natural cycle of climate change, or whether it is caused by human activity.


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A widely accepted hypothesis is that current warming is related, in part, to human activities that add carbon dioxide and other greenhouse gases to the atmosphere.

The burning of fossil fuels, along with the cutting and burning of forests, adds carbon dioxide to the atmosphere faster than the carbon cycle removes it.


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Data show that concentrations of carbon dioxide in the atmosphere have been rising for 200 years.

As a result, the atmosphere’s natural greenhouse effect is intensified, causing the atmosphere to retain more heat.


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Possible Effects of Global Warming

Most recent computer models suggest that average global surface temperatures will increase by 1 to 2 Celsius degrees by the year 2050.


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Sea levels may rise enough to flood coastal areas, affecting coastal ecosystems as well as human communities.

Parts of North America may experience more droughts during the summer growing season.


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New organisms may be able to live in places where they once could not.

Other organisms may become threatened or extinct in areas where they once thrived.


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The Value of a Healthy Biosphere


Ecosystems provide many goods and services, such as water purification and waste recycling.

Ecosystems are also a reservoir of organisms that may one day provide humans with new medicines and new crops.


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People can make wise choices in the use and conservation of resources.

• Avoid using more water than necessary.

• Plant trees to replace those that have been cut down.

• Recycle and reuse trash and other wastes.

• Safely remove hazardous materials.


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6-4


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6-4

An increase in the average temperature of the biosphere is called

a. the greenhouse effect.

b. global warming.

c. ozone depletion.

d. climate control.


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6-4

The geological record indicates that Earth’s climate has

a. remained essentially the same throughout history.

b. been constant until humans have influenced the environment.

c. changed dramatically every 150 years.

d. repeatedly changed over its history.


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6-4

A possible effect of global warming is

a. extinction of organisms in areas where they once thrived.

b. an increase in global surface temperature of 20 Celsius degrees.

c. a sharp decrease in the temperature of the waters off the coast of California.

d. complete elimination of the protective ozone layer in the atmosphere.


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6-4

Depletion of Earth’s protective ozone layer results in

a. a decrease in the amount of heat that reaches the surface.

b. a decrease in the amount of UV radiation that reaches the surface.

c. an increase in the amount of rainfall.

d. an increase in the amount of UV radiation that reaches the surface.


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6-4

The most likely cause of ozone depletion is the

a. addition of carbon dioxide to the atmosphere.

b. increase in UV radiation from the sun.

c. addition of chemicals developed for use in refrigeration and aerosol cans.

d. increase in the amount of smog produced by automobiles.

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Documents

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global climate system

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ozone layer high

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climate conditions

global environment