Biology Ch 18: The Environment The Environment: Global Change

Global Change: The Atmosphere and Ecosystems:  You may be surprised to learn that some kinds of human activity can ultimately influence every ecosystem on Earth.  Human induced environmental changes are affecting ecosystems worldwide and may lead to global change.

Global Change: Acid Rain:  Coal burning power plants send smoke high into the atmosphere through tall smoke stacks, often more than 300 meters (984 feet) tall.  This smoke contains high concentrations of sulfur because the coal that the plants burn is rich in sulfur.

Global Change: Acid Rain:  The intent of those who designed the power plant was to release the sulfur- rich smoke high into the atmosphere, where winds would disperse and dilute it.  Tall smokestacks, first introduced in the mid-1950s, are common in the United States and Europe.

Global Change: Acid Rain:  Scientists have since discovered that the sulfur introduced into the atmosphere by smokestacks can combine with water vapor to produce sulfuric acid.  Rain and snow carry the sulfuric acid back to Earth’s surface.

Global Change: Acid Rain:  This acidified precipitation is called acid rain.  In North America, acid rain is the most severe in the northeastern United States and in southern Canada, areas that are down-wind from coal burning plants in the midwestern United States.

Global Change: Acid Rain:  Recall that the pH of pure water is 7.0  In the northeastern US, rain and snow have an average pH of  This is over 10 times as acidic as the typical values in the rest of the United States.

Global Change: Acid Rain:  Forests in the eastern US and southern Canada are being damaged.  The trees shown at right have been affected by acid rain along with other factors.

Global Change: The Ozone Layer:  Recall from previous lessons that organisms are able to leave the ocean and live on the land because a protective shield of ozone developed in the atmosphere over time, blocking harmful radiation.  Imagine what would happen if this layer were removed?  Alarmingly, it appears that this is happening already. Our ozone layer is being reduced and human industry and activity has played a major role in this reduction.

Global Change: The Ozone Layer:  In 1985, a researcher in Antarctica noticed that ozone levels in the atmosphere seemed to be as much as 35 percent lower than the average values during the 1960s.  Satellite images taken over the South Pole revealed that the ozone concentration was unexpectedly lower over Antarctica than elsewhere in the Earth’s atmosphere.

Global Change: The Ozone Layer:  It was if an “ozone-eater” was causing a mysterious zone of below-normal concentration, an area that researchers called the ozone hole.  Alarmed, scientists examined satellite images taken in previous years. They found that the disintegration of the Earth’s ozone shield was evident as far back as 1978.

Global Change: The Ozone Layer:  Every year since than, more ozone has disappeared and the ozone hole has grown larger.  Moreover, a second smaller hole has appeared over the Arctic.  Because the decrease in ozone allows more ultraviolet radiation to reach earth’s surface, scientists expect an increased incidence of diseases caused by exposure to ultraviolet radiation.  These diseases include skin cancer, cataracts, and cancer of the retina,

Global Change: What is Destroying Ozone?  The major cause of ozone destruction is a class of chemicals called chlorofluorocarbons (CFCs).  Invented in the 1920s, CFCs were considered extremely stable, supposedly harmless, and nearly ideal heat exchangers.

Global Change: What is Destroying Ozone?  Throughout the world, CFCs were commonly used in refrigerators and air conditioners, as aerosol propellants in spray cans, and as foaming agents in the production of plastic-foam cups and containers.  Though CFCs were escaping into the atmosphere, at first no one worried.

Global Change: What is Destroying Ozone?  By 1985, the scientific community had learned that CFCs were the primary cause of the ozone hole.  High in the atmosphere, ultraviolet radiation from the sun is able to break the usually stable bonds in CFCs.  The resulting free-chlorine atoms then enter into a series of reactions that destroy ozone.

Global Change: What is Destroying Ozone?  As a result of this discovery, CFCs have been banned as aerosol propellants in spray cans in the United States.  Today many countries limit or ban the use of CFCs.

Global Change: Global Temperatures:  The average global temperature has been steadily increasing for more than a century, particularly since the 1950s.  In Earth’s long history there have been many such periods of global warming, often followed by centuries of cold.  Scientists hypothesize that sunspot cycles may contribute to these cyclic changes in global temperature. Many scientists however believe that human activity has much to do with this increase in temperature.

Global Change: The Greenhouse Effect:  Our planet would be as cold as the moon except for the insulating effects of certain gases, called greenhouse gases, such as water vapor, carbon dioxide, methane, and nitrous oxide in the atmosphere.  The chemical bonds in carbon dioxide molecules absorb solar energy as heat radiates from Earth.

Global Change: The Greenhouse Effect:  This process, called the greenhouse effect, traps heat within the atmosphere in the same way glass traps heat within a greenhouse.  There has been a large increase in carbon dioxide in the Earth’s atmosphere in recent times.  This increase seems to be related to the burning of fossil fuels that has accompanied the clearing of forests and urban industrialization.

Global Change: Is Global Warming Occurring:  If we look at a chart of the average temperature since 1880 and compare it with a chart of the average concentration of carbon dioxide in our atmosphere, we see a clear correlation between the two.  The correlation of increasing temperatures with increasing carbon dioxide levels is very close.  This evidence has many scientists convinced temperature and carbon dioxide levels are related.

Global Change: Is Global Warming Occurring:  In science however, correlation does not prove cause and effect.  Both global temperatures and levels of greenhouses may be changing because of other variables that have not been recognized yet.  Some countries take seriously the possibility that increasing greenhouse gases play a role in global warming.

Global Change: Is Global Warming Occurring:  These countries are attempting to formulate international treaties that will place limits on greenhouse emissions.  The matter remains controversial and the role that greenhouse gases play in global warming are a matter of argument and discussion.