• Over a short time period, human activities have affected global ecosystems in ways that harm humans and other species. Human impacts range from local pollution to global change in ecosystems.

• Industrial chemicals called chlorofluorocarbons (CFCs) act as catalysts in chemical reactions that break down O3 molecules in the ozone layer. Most countries have banned CFCs, and the ozone layer seems to be recovering.

• The correlation of increasing atmospheric CO2 and rising global temperature suggests a cause-and-effect relationship. Considering several types of evidence, many scientists have concluded that increased CO2 levels have caused warmer surface temperatures on Earth.

• Certain air pollutants cause acid precipitation, which harms or kills many organisms.

• The release of toxic chemicals, such as DDT, into the biosphere can impact ecosystems in many ways, especially when chemicals undergo biological magnification.

• Human impacts on the environment are causing an increasing number of extinctions. Important causes of extinctions are habitat destruction, the transfer of invasive species to new habitats, and overharvesting or hunting. This loss of species has both known and unknown effects on ecosystems.

• Current levels of human resource use are probably not sustainable.

Vocabulary smog (p. 440)

chlorofluorocarbon (CFC)

acid precipitation (p. 441) biological magnification

extinction (p. 442) keystone species (p. 443)

sustainability (p. 444)

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