45: Human Impact on the Environment
An Indifference of
1. Humans have been straining these engines without appreciating that they can crack.
2. For example, our carbon dioxide waste is contributing to a “greenhouse effect” (global warming).
B. Population growth and individual demands are stressing the environment.
I. Air Pollution—Prime Examples
A. Pollutants are substances with which ecosystems have no prior evolutionary experience and therefore cannot deal with them.
1. Air pollutants include carbon dioxide, oxides of nitrogen and sulfur, and chlorofluorocarbons.
2. Each day 700,000 metric tons of pollutants are dumped into the atmosphere in the United States alone.
1. Thermal inversions can trap pollutants close to the ground.
2. Industrial smog is gray air found in industrial cities that burn fossil fuel.
3. Photochemical smog is brown air found in large cities in warm climates; for example, gases from cars form car exhaust.
C. Acid Deposition
1. Burning coal produces sulfur dioxides.
2. Burning fossil fuels and fertilizers results in nitrogen oxides.
3. Tiny particles of these oxides can fall to the earth in two forms: dry acid deposition or acid rain.
II. Ozone Thinning—Global Legacy of Air Pollution
A. Ozone in the lower stratosphere absorbs most of the ultraviolet radiation from the sun.
1. The thinning of the ozone layer has produced an ozone hole over Antarctica.
2. In response, skin cancer has increased, cataracts may increase, and phytoplankton may be affected.
B. Chlorofluorocarbons (CFCs) seem to be the cause—one chlorine atom can convert 10,000 ozone molecules to oxygen.
III. Where to Put Solid Wastes? Where to Produce Food?
A. Oh Bury Me Not, In Our Own Garbage
1. Paper products and nonreturnable bottles and cans are perhaps our biggest problems.
2. We face a challenge to move from a “throwaway” society to one of conservation and reuse.
B. Converting Marginal Lands for Agriculture
1. Almost 21% of land is used for agriculture; another 28% is available but may not be worth the cost.
2. The green revolution has increased crop yields but uses many times more energy and mineral resources.
3. A growing human population is moving into marginal lands to meet its increasing needs.
IV. Deforestation—An Assault on Finite Resources
A. Forests are watersheds; they control erosion, flooding, and sediment buildup in rivers and lakes.
1. Deforestation can reduce fertility, change rainfall patterns, increase temperatures, and increase carbon dioxide.
2. Clearing large tracts of tropical forests may have global repercussions, such as alteration of rates of evaporation, transpiration, runoff, and rainfall as wells as photosynthetic activity rates.
B. In shifting cultivation (once called slash-and-burn agriculture) trees are cut, the land used for a few growing seasons and then abandoned as fertility plummets.
V. Focus on Bioethics: You and the Tropical Rain Forest
VI. Who Trades Grasslands for Deserts?
A. Desertification is the conversion of grasslands and croplands to desertlike conditions.
1. The term also applies when agricultural productivity drops by ten percent or more.
2. At least 200,000 square kilometers are being converted annually.
B. Large-scale desertification is caused by overgrazing of cattle (non-native) on marginal lands.
VII. A Global Water Crisis
A. Most of the earth's water is too salty for human consumption or for agriculture; desalination is very costly
B. Consequences of Heavy Irrigation
1. Large-scale agriculture accounts for nearly two-thirds of the human population's use of fresh water.
2. Salt buildup (salinization) of the soil and waterlogging can result.
3. Withdrawal of underground water causes water tables to drop.
C. Water Pollution
1. Human waste, insecticides, herbicides, chemicals, radioactive materials, and heat can pollute water.
2. Wastewater treatment occurs on as many as three levels:
a. Primary treatment removes and then burns sludge before it is dumped in landfills; chlorine is added to water.
b. Secondary treatment uses microbes to degrade organic matter—nitrates, viruses, toxic substances remain.
c. Tertiary treatment uses experimental methods to remove solids, phosphates, organics, etc.; it is used on only about 5% of the nation’s wastewater.
D. The Coming Water Wars
1. In the past decade, thirty-three nations have engaged in conflicts over reductions in water flow, pollution, and silt buildup.
2. By restricting water flow, countries upstream may attempt to influence political behavior in countries downstream.
VIII. A Question of Energy Inputs
A. Increases in human population and extravagant life-styles increase consumption.
B. Fossil Fuels
1. Fossil fuels are a limited resource, extraction costs are increasing, and atmospheric levels of carbon dioxide and sulfur dioxides are also increasing.
2. Extraction and use of abundant reserves of oil shale and coal are not “environmentally attractive.”
C. Nuclear Energy
1. With nuclear energy, the net energy produced is low and the cost high compared with coal-burning plants.
2. Meltdowns may release large amounts of radioactivity to the environment.
3. Nuclear waste is so radioactive that it must be isolated for 10,000 years.
IX. Alternative Energy Sources
A. Solar-Hydrogen Energy
1. Solar-hydrogen energy is an attractive technology because it depends on the renewable energy source—the sun.
2. Photovoltaic cells produce an electric current that splits water into oxygen and hydrogen gas which can be used directly as fuel or to produce electricity.
B. Wind Energy
1. Where winds travel faster than 7.5 meters per second, wind turbines are cost-effective producers of electricity.
2. Because winds do not blow on a regular schedule, wind turbines cannot be the exclusive source of energy.
C. What About Fusion Power?
1. Temperatures like those on the sun cause atomic nuclei to fuse and release energy.
2. Fusion power on Earth is possible but many obstacles make the technology a distant possibility.
X. Focus On Bioethics: Biological Principles and the Human Imperative